Anybody know why RX8 has little torque compared to most piston engines? Is there any possible solution like to make 250 HP and at least like 200 ft.lbs. for the RX8's rotary engine or is it just impossible without turbo? Would lighter rotors make any extra torque?

I believe the "Stroke" in a piston engine helps create the greater torque... a rotary by design doesn't have that kind of stroke in its eccentric movement. A more erratic eccentricity would probably help, but it would suffer in its ability to rev high. However, for what torque it does have, there is a rather wide torque band compared to a piston engine. Anyone else have some ideas?

The Geo Metro sized engine is one of the big reasons. While lower displacement engines can make up HP by spinning faster than typical higher displacement engines, torque seems to have a direct relationship with the size of the engine. If you compare an equivelant displaced inline 4 between Honda and GM for example, the torque ratings are very similar - what makes Honda's better is its ability to make more HP at higher RPM's.

The Renesis is effectively a 2.6 L so you wouldn't expect it to produce loads of torque. The cure for low torque is low gearing - this gives you more torque at the wheels (which is what really counts). The RX-8 has pretty low gearing, if you ignore 6th gear.

The price you pay for the low gearing is a higher revving engine. For a piston engine this is not always a great solution as it means much more noise and vibration (especially for a 4 cylinder). But it's fine for a rotary because they are so smooth anyway.

Torque is really nothing more than force. Force is mass x accelleration. The pistons, rods, and crankshaft in a big v8 weigh a LOT more than our 2 rotors and e-shaft. When they get moving they can produce more force due to the sheer mass. Combine this with big displacement, the ability to move lots of air really fast and the ability to accellerate those heavy parts and you get lots of torque.

A good way to think of it is this. Let's say I had two viper engines. 500 cubic inch V10. I leave one internally stock. The other I replace all of the internals with parts that weigh half as much, but can rev twice as high. At 4000 RPM's, that stock viper engine, with the heavier internals, will be producing as much torque as our custom engine would produce at 8000 RPMs.

However when it comes down to it, torque is just a pretty number that sells products. It's really good for smoking tires and breaking driveline parts though. There was a really good writeup that I saw that explained all of this stuff in all of it gruesome mathematical glory. There's a lot of sites that explain the horsepower v.s torque relationship, how torque is really only important as a factor of horsepower. Just do a google search for something like "horsepower vs torque". It's kinda funny how many sites there are that treat torque as the end-all of racing. Coincidentally those sites are run by v8 guys. ;) So before you bash me for saying that torque on it's own is nothing...go out there on the internet, find the info and do your own math, and make your own decisions about it. :)

Follow this link:

http://www.yawpower.com/tqvshp.html

It says it all
;)

ok, wow. a few weird ideas out there.

for you guys thinking that it's a 2.6L, even when measuring torque at the crank, i'm sorry to report that you're incorrect my friend.
when you're measuring on a dyno how much force per turn you're making, then multiplying by the speed of the engine to get power, you're not counting two turns together, it's just the one. so, yes, the 1.3L displacement has a lot to do with it.

another idea which hit the mark is the eccentricity: the longer lever on presumably equal force generated by combustion would give more torque at the flywheel, but would be rpm inhibitive (that's why, along with a few other factors, why strokes in high horsepower machines are usually fairly small).

just so we don't have any more physics 11 mix-ups, it's not F = M * A in this case (the relationship derived from A = F/M), but force = pressure * area, initially, which is why displacement has such a huge todo about making power.

there are two ways you can do it, it being make power. you can take a small force (say, the force generated by an all-motor 1.0L I4) and apply it repeatedly at a very high rate (rev it up to 13 000 rpm), thus equalling x amount of power. or you can take a large amount of force (like a 3.5L V6) and multiply that at a lower rate (say, 6 500 rpm), to make y amount of power. which is a better way?? well it depends on a host of other factors.

anyways, that was a little off track.
the reason the 13B-MSP has low torque is because of its small displacement, and that it only has a very small stroke (15, or 25mm or something... the difference between the centre of rotation and the centre of the e-shaft), although this lever is acted on for 270* of rotation instead of the normal 180*. blah blah blah, off track again.

anyways Haris, you could make a rotary engine which made only 250hp on 200ftlbs of torque, but it'd be... well, yeah. a 3 rotor tuned to make all low-end horsepower would do just the trick.
what you have to recognize though, is that not only is this terribly wasteful (that's a very low hp number for a 3 rotor), but it's not the torque that matters anyway, but only the horsepower (as illustrated in Paul's article that AlexCineros linked to) in the lower reaches of the rpm band.

and as for lighter rotors, no, they wouldn't help in making more torque, but if applied correctly would be an important part in making very high horsepower all-motor, with the revs.

So can rotary be used in trucks and have like 15,000 lbs. towing capacity, or is it just basically for sports cars?

I'm just going to cut and paste my response to the why 1.3 thread. Here is everything you ever wanted to know in an extremely long post.

First of all you may just want to print this as it is really freaking long!

I wrote this last summer for another forum so here it is reposted here.

The rotary engine is a 6 stroke internal combustion engine. I know, people will probably start screaming at me for this so lets get into a little explanation as to why and how typical mathematical formulas for piston engines don't work.

First of all, lets get the terms "stroke" and "cycle" defined (Some of you get your heads out of the gutter!) since everyone commonly gets these terms interchanged. They are not the same thing. Every internal combustion engine whether it is a 2 stroke, 4 stroke, diesel, gasolines, propane injected, etc. is a 4 cycle engine. Why? All of these engines take in air (intake), compress the air (compression), ignite the air whether by spark plug or glow plug (ignition), and expell it out the tailpipe (exhaust). There you go 4 cycles. Simple isn't it. The term "stroke" in this context refers to how many times the crankshaft or eccentric shaft makes a piston go up or down to complete the cycle.

The connecting rods and pistons are just an extension of the offset lobes of the crankshaft. This is also true in regards to a rotor and eccentric shaft. When the lobe rotates upward, the piston goes up. When the lobe rotates down, the piston goes down. Every time it moves one way is considered a stroke. In a 2 stroke engine, all 4 phases or cycles of the combustion process are completed in only 2 strokes of the piston, 1 up and 1 down. This is only 1 complete revolution of the crankshaft. In a 4 stroke engine, it takes 4 strokes of the piston, up, down, up, down to go through the complete combustion process. This is 2 complete revolutions of the crankshaft. It's all a very simple mathematical relationship.

Now lets go look at the workings of a rotary engine. If we look at a rotary engine eccentric shaft and compare it to a piston engine crankshaft, we see essentially the same piece. Both have lobes and because of this both engines will have a stroke length, even the rotating rotary. It doesn't matter if it is a piston going back and forth or a rotor going round and round. The crankshaft motion remains the same. On a rotary engine, the rotors are spinning at exactly 1/3 the speed of the eccentric shaft. From the time that the air entering one chamber goes through the combustion phases to the time it leaves the engine from the same chamber (rotor face), the eccentric shaft has gone around 3 complete times unlike a 4 strokes 2 times or a 2 strokes 1 time. If we do the math we see that the lobes of the eccentric shaft must have gone up and down 6 times (up, down, up, down, up, down). Since it does this process the exact same way every time for every rotor face, it is a 6 stroke engine. Thats right the rotary engine is a 6 stroke! Do not confuse these strokes with the 4 internal cycles that every engine has!

Let's sum this up in a simple chart to visually explain how this works.

2 stroke engine (up,down) - 1 complete crankshaft revolution

4 stroke engine (up, down, up, down) - 2 complete crankshaft revolutions.

6 stroke (rotary) engine (up, down, up, down, up, down) - 3 complete crankshaft (eccentric shaft) revolutions.

See a pattern? All of these engines though are still 4 cycle engines! They are different stroke engines though so the amount of work they do per time is very different. A 2 stroke engine does twice the work per amount of time that a 4 stroke does. Don't believe me? Go race 2-80cc motorcycles, 1-2 stroke and 1-4 stroke and see who wins! This must mean that the rotary engine does the least amount of work per time than both other engine types. Yes it does. But, unlike a piston engine, it uses 3 sides of it's piston (rotor) at a time. In reality it makes no difference if we have 1 rotor with 3 usable faces or 6 rotors with 1 usable face each as in a piston engine.

Here's a little info on how to properly figure out displacement on a rotary engine. Everyone argues that it is really a 1.3 liter while others argue that it is really a 2.6 liter engine. They are both wrong! If we look at how a piston engines volume is calculated we arrive at a displacement based on total swept volume of every piston added together. It is not based on rpm. On a rotary, displacement is figured using one rotor face in one complete revolution then multiplyed by 2. This only leaves the total for 2 combustion chambers though and the rotary has 6! Since the volume of a 13b rotary is rated at 1.3 liters (only 2 combustion chambers) it really adds up to 3.9 liters!!! I can hear it now, "...but we only have 2 rotors!" So what. Like I said it makes no difference if there are 2 rotors with 6 faces or 6 rotors with one face each. the total is always 6 and the base numbers are only based on 2 chambers. The rotary merely does 3 times the work in a package 1/3 the size. It's just a 3.9 liter engine crammed into a 1.3 liter body. Just so none of you start a fight over this, I will explain this later so don't chastise me yet!!!

In case anyone is curious I did some math to determine what the 13B rotary would be sized at if it were a piston engine. The results are pretty neat. First of all the rotary would be a 3.9 liter, 6 cylinder engine. It would be a 6 stroke. Each cylinder would be 6.54" across (damn big piston!) but the stroke length would only be 1.18" in length peak to peak. Not much there. Interesting isn't it. Now just imagine a way to make all this work with only 2 intake runners!

In all fairness to the terms I have used, the word "stroke" can be interchanged with the word "cycle" since both technically have the same definition. The terms "periods", "quarters", or "phases" can also be used correctly. I merely wrote it the way I did to get a certain mental picture going.

I have already dealt with why the rotary engine is really a 6 stroke engine and why displacement is really 3.9 liters and not 1.3 liters. Now I need to explain why the rotary engine doesn't have the torque or horsepower of a good 3.9 liter engine or why it doesn't get the gas mileage of a 1.3 liter engine. The world has always wondered so here's why.

Remember that I stated that the true displacement of the rotary engine, if figured out according to the way piston engine volumes are calculated, is according to the total number of rotor faces and not the number of rotors, nor does it have anything to do with rpm. This added up to 3.9 liters for a 2 rotor 13B engine and not the published spec of 1.3 liters. They just crammed all 3.9 liters into a 1.3 liter body. If the engine is really a 3.9 liter engine then why doesn't it have the low end torque of a 3.9 liter engine? This has a very simple answer. Lack of leverage. OK, what the hell does that mean?

First of all we must figure out what a lever is. It is a device that multiplies mechanical advantage over an object to do the same amount of work with a smaller amout of effort. Another way to look at it is to do a greater amount of work with the same amount of effort. It's the same thing. Let's look at leverage differences as an example in a piston engine.

What happens to a piston engine when we make it a "stroker"? Ignoring a host of other variables, it gains torque. It also gains horsepower but they are both a fixed mathematical ratio between each other and you can't increase or decrease one without the other. Why did it gain torque? Greater mechanical advantage or leverage over the crankshaft. The reason being is that on a stroker crankshaft as opposed to the stock crankshaft, the lobe centerline is farther out from the rotational centerline of the crankshaft. This increases the leverage that the piston has over the crankshaft. Don't believe me? Try this. Get a short pole and hold it at the end straight out away from your body. Attach a 10 lb weight to it exactly 1 foot away from your hands. The weight is exerting exactly 10 ft. lbs. of torque on your hands. Now move that weight out away from you to 2 feet away from your hands. Now the same weight is exerting 20 ft. lbs. of torque on your hands. You have just in essence made a "stroker". Now let's get back to the engine.

Now we know that the greater the stroke length, the greater the engine torque. As I stated, the rotary engine only has an effective stroke length of 1.18". My weedeater has that! There is not very much mechanical advantage over the eccentric shaft. This still doesn't explain everything though.

Remember, I stated that if the 13B rotary were a piston engine it would have pistons 6.54" across. Now we just discovered another enemy of efficiency, flame front speed. When the spark plug ignites the mixture in the engine, it doesn't just ignite everything all at once. The spark ignites at the plug and then has to travel outward away from the plug at a certain rate of speed. While this only takes milliseconds, this amount of time gets more critical the higher the rpm gets due to the shorter amount of available time. The result is that as rpm's rise efficiency decreases. The larger the area of the piston, the farther the flame front has to travel and the greater the chance that all of the mixture does not get ignited when it should. Just can't go far enough fast enough. Todays rotaries have 2 sparkplugs per chamber to help combat this problem. Varying their ignition time in relation to each other even helps somewhat with power and emission. That's right they don't necessarily fire together even though they are in the same chamber. This can get complex so I will not deal with it at this time. Some race engines even have 3 plugs per chamber to improve efficiency and ignition wave front speed. On piston engines, Mercedes has capitalized on this and uses 2 plugs per cylinder in some of their higher end cars. Do they know something others don't?

There is also one more aspect that affects it. Remember that the rotary is a 6 stroke engine. A 2 stroke engine does twice the amount of work per amount of time that a 4 stroke engine does. A 4 stroke engine does 50% more work per amount of time that a 6 stroke does. The rotary engine does less work per eccentric shaft rotation than your typical 4 stroke counterpart. All of these characteristics combine to make an engine that has relatively little low end power and needs to be revved up to be truly powerful.

I make it sound like we should have less torque than a 1.3 liter engine due to the above reasons. This isn't true though. Remember that we still have a 3.9 liter engine even though it only uses 2 lobes on the eccentric shaft. We should not expect to develop the torque numbers of a 1.3 liter engine. It should settle in somewhere around 50% less than a 3.9 liter engine which would put it around equal to a 2.6 liter engine in power.

These traits of the rotary engine are also why the engine gets worse gas mileage than your typical 1.3 liter engine. Hell it gets worse gas mileage than your typical 2.6 liter engine. Another aspect that affects this is port timing and duration. If we had a piston engine of 2.6 liters in size that had the same intake and exhaust timing as the rotary then it would get comparable gas mileage to the rotary. The 12A/13B rotary though have much more exhaust duration than intake duration due to the peripheral exhaust port location. This contributes to several factors which decrease efficiency. Exhaust gas dilution is one of them. For each stroke there is a small amount of overlap. The exhaust ports and intake ports are open to the same chamber at the same time for a short amount of time as measured in degrees of eccentric shaft rotation. The higher the rpm's the less important this becomes since air velocity will generally keep the gasses where we want them to go. At lower rpm's though the intake and exhaust air velocity is not very high. This will cause some exhaust to go back through the combustion chamber again. When this happens volumetric efficiency decreases and there is less room for fresh air to fit inside the combustion space. Also this recirculated exhaust gas is very hot. A hotter air molecule is larger than a cold one which means a fewer number of molecules can fit in the same area per amount of pressure exerted on them. Another aspect of the rotary's peripheral exhaust port configuration that contributes to less low end power and greater fuel consumption is its incredibly long duration or time it is open for. Unfortunately when we make the port bigger we also change it's timing. We don't have the luxury of being able to mill out a head to accept a larger valve while still being able to use the same cam. The timing is really only optimized for high rpm use. We are leaving it open for too long which gets back to the whole overlap problem. Again, all of this is just a generalization and can be affected by how well the intake and exhaust flow and how well they can scavenge. The affects of scavenging, intake design, helmholtz effect, and proper exhaust design are all out of the scope of this article. So just assume it is an even world.

Luckily there is a cure for this. It is called Renesis! It is the new 13B based rotary engine in the new Mazda RX-8. The exhaust ports are no longer in the periphery of the chamber but have rather been moved to the side housings. This allowed the designers to more appropriately optimize the port timing duration. The location also allows more port area leaving the engine. So now we have more area to flow air out of faster. This new location also completely got rid of the port overlap. There is actually 64 degrees of dwell. This amount of dwell was originally greater in the early test engine called the MSP-RE since it had the intake timing of the '84-'91 n/a RX-7's 6 port engine. However dwell is only useful if you just have enough to get the job done but not so much that you are getting losses from it. Because of this Mazda engineers learned that they could open the intake earlier than previously and still maintain all of the other good aspects of the new exhaust layout. A bigger intake port = more time for air to enter and a greater cfm rating through the port. Less turbulence through the port as well. Less overlap gives us less dilution of the intake air and a cooler intake charge. More available room for incoming air. Volumetric efficiency increases. Since efficiency goes up, our use of gas gets more efficient. In other words it takes less fuel to do the same amount of work. The result, better gas mileage. With todays gas prices this is a very welcome thing. The efficiency increase also means that emissions characteristics are also improved. Another bonus with todays laws concerning air quality.

So after reading this you are probably wondering why in the world anyone would want to use one of these engines. First, and most obvious is size. They crammed a 3.9 liter engine, or more appropriately a 2.6 usable liter engine into a 1.3 liter body. Second, it is just such a simple design. There are only 3 moving parts. Fewer moving parts have less frictional losses. Also fewer moving parts have less chance statistically of failure. The more it moves, the more chances you have for failure. Third, nothing moves back and forth. So what? A piston stopping and changing direction exerts alot of stress on everything from the crankshaft to the connecting rods, to the pistons, to the wristpins, etc. Lets not also forget the stresses on the valves for being slammed open and shut as well as the temperature extremes they see during the combustion cycle. A body in motion tends to stay in motion. It is a very unnatural act to change direction suddenly or at all for that matter. A rotary just spins away in the same direction. Yes the lobes of the eccentric shaft do see stress but remember that we don't have very much leverage over them. The rotors are also exerting some of their rotational stress on the stationary gears as well so some stress is never transmitted to the eccentric shaft from the rotors. The lack of stroke length and pure rotational motional do make it very naturally adapted to high rpm use. If we look at really high horsepower piston race engines, their stroke length has been shortened to reduce the stresses to all of the engine components at high rpms. The last and most important reason why the rotary engine is still a popular engine despite it's shortcomings is because it is different. There is always something to be said for individuality and uniqueness. If you own a piston engine it doesn't matter how big it is or if it is made by Chevrolet or Honda. It is still the same device.

Just to shoot down right now any arguments on displacement think about this.

The 13B rotary engine is a 1.3 liter. Yes.
The 13B rotary engine is a 2.6 liter. Yes.
The 13B rotary engine is a 3.9 liter. Yes.

Notice that all of these statements are TRUE!!! That's right there is a truth to all of those statements. Go read the whole thing again. To understand why this is so, lets define truth. Truth can be defined in a couple of ways: Anything that is not false (none of those statements is) or it can be defined as: One's individual interpretation of presented facts. This herein is the source of our debate. We can't change the facts no matter how hard we try. Arguing won't do it. What is debatable however, is each individual's interpretation of facts. If your interpretation doesn't match someone else's, you argue about it.

Here are the facts: The rotary engine as rated by Mazda is 1.3 liters because each individual rotor, following one face of one rotor through the complete cycle, has a swept displacement of 654cc or .65 liters. Multiply this times 2 rotors to achieve 1.3. Since this only accounts for 2 of the total of 6 rotor faces, we multiply our answer by 3 to get an actual displacement of 3.9 liters. However since the rotary engine is a 6 stroke engine and not a 4 stroke engine since it takes 3 complete eccentric shaft revolutions to fire all faces instead of the typical engine's 2, it only does 66% the work of a 4 stroke 3.9 liter engine. Calculating for this we divide 3.9 by 1.5 to get a total of 2.6 liters equivalent work to a 4 stroke piston engine. All of this from a 1.3 liter in physical size package.

No one can argue that this is not correct and any response saying otherwise will have been explained by what I just said. Any debate will only focus on one aspect and not the total facts.

Just to put a cap on this whole thing: If at any time you try to calculate proper sizing for a turbo, intake manifold runners, intake plenum size, exhaust size, etc, and you try to use the 1.3 liter number in your equations, you will be way, way, way off!!!!!!!!! There are only 2 ways to flow more air: increase displacement or increase rpm. A 1.6 liter Honda engine doesn't flow anywhere even remotely near what a 13B (1.3 liter) flows per the same rpm. Just some food for thought.

Rebut that! I need the entertainment! Hehe!!!

If you got this far, give yourself a cookie! My carpal tunnel syndrome is starting to get bad

Let's say I had two viper engines. 500 cubic inch V10. I leave one internally stock. The other I replace all of the internals with parts that weigh half as much, but can rev twice as high. At 4000 RPM's, that stock viper engine, with the heavier internals, will be producing as much torque as our custom engine would produce at 8000 RPMs.

I truly believe all of this is wrong. The heavier components have more inertia and are more difficult to move, thus have more losses. I think that the custom engine with 50% lighter internals (Titanium?) would give higher torque at all rpm ranges (ignoring a lot of other variables and assuming the components are equally strong as the stock heavier ones). Any expert care to comment? Rotarygod?

Oh and I already read your previous post on the other thread, Rotarygod. Very insightful. I read it againg here, I have a headache! :p

Give me your address so I can send you a packet of aspirin! ;)

I'll respond to the rest after I think it out well. I don't want to contradict myself but I do also find it to be wrong.

I'm not sure how this relates to the actual reason why we have low torque, but I have a theory. I do know that torque doesn't equal mass times acceleration nor pressure times acceleration.

Torque is equal to the moment of inertia times the angular acceleration. The moment of inertia is equal to mass times distance squared. In the case of a piston engine (a uniform rod), the moment of inertia is 1/4 times the mass of the rod times the distance from its center of mass to the edge squared. Therefore, the mass and the size of the pistons probably have a lot to do with torque. Also, the sheer number of pistons should add to the total torque on the crankshaft.

As for the rotary, a wankle is similar to a uniform ring which has a moment of inertia of MR^2 instead of 1/4*MR^2 like the rod (M being mass and R being distance). It would require quite a bit of calculus to determine the exact moment of inertia of a wankle, but if you follow this logic, then a wankle should have a higher moment of inertia than a piston and therefore more torque. However, it comes down to quantity over quality and most piston engines have more than two pistons.

I'm not sure if my logic is correct, but that is what my mechanical physics class at Texas A&M has taught me.

You have to take into account that even while a lot of mass (pistons, rods) will help the engine work while going down, it will actually make the engine work harder when pushing them up and suddenly changing direction. Remember Newton? A mass (piston) will keep going in the same direction unless a force is applied to it; the more mass, the more force it needs to move and change direction. Piston movement is completely linear and crankshaft movement is completely rotational, the rod's movement is more difficult to analyze. While the crankshaft will want to keep spinning, the constant change in direction of the pistons keep it from doing it.

I'm going to play captain obvious here...

the rotor/eccentric shaft movement effectively creates a 3:1 gearing... or the eccentric shaft spins 3x faster then the rotors. Using the laws of physics and conservation of power, if you increase the speed by 3x through gearing you just decreased the torque by 1/3.

You guys need to think a little more simply here about torque vs engine parts weight. Try this little experiment. Go out to your vice and clamp a 1 ft long rod in the vice. Now attach a 10 lb. weight to the end of the rod. You have 10 ft pounds of torque being exerted on the vice or you can do it with a 10 pound rod with a 1 lb. weight. This is only true if the rod weighed nothing. If the rod weighed 10 lbs then the longer rod would "effectively" add more weight since more of the weight is farther out from the centerline. Both setups would weigh the same but the one with the greater amount of weight farther out would appear to the vice as being heavier and in turn exerting more torque on the vice. Remember that torque has absolutely nothing to do with movement. Some of you guys think you know where I'm going with this don't you? However just as a heavier rotating assembly is easier to move downward in stroke it is also harder to move upwards as well. It's that whole gravity thing that everyone talked about in school. You need to remember that torque is affected by many things. Displacement is one very important aspect but its leverage on the crank is also very important. While the weight of the components will affect it some, halving the weight will not yield half the torque. This would only be true if we also halved the combustion. Weight will affect it some but you probably won't feel as if you've lost torque. In fact the result will be that it feels more powerful. Remember that all that extra weight also takes power to move. Remember again that torque has nothing to do with movement however movement is a funtcion of horsepower which is in a fixed relationship with torque. Less weight is easier for an engine to get moving and therefore there is more usable power. The amount of air in the combustion chamber and the compression ratio also affect how hard an engine is to turn. A higher compression ratio will yield a higher torque. Weight is a factor but you actually want less weight to get more power. Also remember that a different intake or exhaust will tune for more power/torque at a different rpm. There are too many variables to just base speculation off of just one thing. Engine designers want to get lighter and lighter assemblies. This builds horsepower and makes you much faster. It is also much less stress on engine internals. Maybe a small amount of low end torque is lost but then again it did take power away to get that extra weight moving so maybe not. It is not a set relationship that torque is halved if weight is halved. That is just plain wrong. It is kind of funny that if more weight were so important then why do lighter flywheels give more wheel horsepower on the dyno and make your car accelerate faster? Remember that since torque and horsepower are a fixed ratio that if the car is faster and shows more power, it can't have less torque. Even if it does, it will be very low in the rpm range and not worth worrying about. You would think that everyone would want a heavier flywheel for street use wouldn't you? Before anyone says that they do, while true it is only because it is easier to drive since the engine does not rev up or down as fast. This leads to smoother shifts with less rpm loss in between them but is not due to torque. Ever weighed an automatic cars' starter wheel which would be the equivalent? It is pretty damn light. That's my take on it. The lighter the better.

Remember that torque has absolutely nothing to do with movement.

I can tell you are getting a lot of your information from the yawpower article but torque definately has a lot to do with movement. Without an angular acelleration, there can be no torque. That I am 100% positive about.

Inertia is the property of an object to resist change in motion. What your talking about with the 10lb weight on the end of a pole is inertia. An increase in inertia will increase torque. Inertia is completely independent of motion.

I do agree that if weight is halved than torque will not be halved because there are more factors than just weight at work here.

The lighter flywheel as you said will cause the engine to rev up faster which would increase angular acelleration and lead to more torque that way. As i said its not just weight at work here.

I believe that the pistons are the means of acellerating the connecting rods and the moment of inertia of the crankshaft combined with that acelleration provide you with your torque. Factors such as distance from the center of mass of the crankshaft to connecting rods, the mass of the crankshaft, and the acelleration of the connecting rods make up torque. This seems like it would make the most logical sense. I was wrong earlier when trying to find torque by taking into account the inertia of the pistons themselves.

This is the same person as GooOnYou fyi.

Originally posted by Shard
I believe that the pistons are the means of acellerating the connecting rods and the moment of inertia of the crankshaft combined with that acelleration provide you with your torque.

The pistons are there to convert the pressure of combustion into a linear force that is transmitted thru the conn rod to the crankshaft and converted into rotation. The mass of the piston actually robs power, that's why manufacturers try to go as light as possible while retaining strenght.

Rotarygod, thanks for your reply. It's a more elaborate way to explain what I already said. :D

Originally posted by Shard
I can tell you are getting a lot of your information from the yawpower article but torque definately has a lot to do with movement. Without an angular acelleration, there can be no torque. That I am 100% positive about.



edit: to remove the egg from my face. what was i thinking?

nope torque is just the meaurement of the force. it is not a measure of distance or time and neither of those figure into the measure of torque

Do you know what force is? Its a mass times acelleration. Acelleration is distance divided by time squared which incorporates both DISTANCE AND TIME. You contradict yourself.

As for neit, he just restated what i said.

Check this article out.

http://science.howstuffworks.com/fpte3.htm

Oh and the moment of inertia times angular acelleration is equal to the force times distance which both are ways of finding torque.

MR^2*(A/R) = MAR

MR^2 is inertia
A/R is angular acelleration
MA is force
R is distance

Cancel one of the Rs from the left side because you have R^2/R and you get MAR = MAR.

Lesson in physics is over.

sorry there, i lost my mind. i edited my post to reflect that. T is a measure of rotaional force so of course it incorporates distance and time. i'll try to figure out what i meant to say and state it again later.

No problem. Physics is my territory so I love an in depth discussion about this kind of stuff :D

If force and torque require movement, then I don't apply any force to the ground while standing still... (Yay! I don't weight anything!); a mechanic doesn't apply any force/torque while trying to remove a very tight bolt or nut... hmm, think about that. How about force distribution in buildings, bridges, beams, etc., nothing is moving.
A force and therefore torque (force times torque arm length) can be applied without any movement or distance been involved. When a force or torque causes something to move it is doing Work.
We all need to review our Physics classes

Recheck this article out.

http://science.howstuffworks.com/fpte3.htm :D

right-

Main Entry: 2torque
Function: noun
Etymology: Latin torquEre to twist
Date: circa 1884
1 : a force that produces or tends to produce rotation or torsion

so it doesn't have to be moving, it is used as a measure of the force if it did cause movement or that would be required to make something move. you don't have to have movement to have force but you need to have the potential for a rotation to have torque. i believe that is what i was trying to say earlier. and if i am right this time than it is most definetly what i meant. ;)

Anyway, back to the original question. Reasons why the renesis could create less torque:

1) if it has a crankshaft of smaller mass compared to that of a high torque piston engine.

2) if the distance between the center of mass of the crankshaft to the perpendicular component of centripetal force acting on the crankshaft (aka the connecting rods) is very small. Therefore, the longer the connecting rod distance from the center of the crankshaft, the more torque. The renesis, however, does not have connecting rods. The force is acting directly on the outside of the crankshaft so the distance from the center of mass of the crankshaft to the perpendicular component of force is very small which in turn creates less torque. This i believe is the main reason for the loss of torque in the renesis.

3) another reason could be that the engine fails to put out enough force tangent to the edge of the crankshaft for it to be able to create loads of torque but i don't think this is an issue.

If i think of other reasons I will post them later.

Good point ya'll bring up.

Keep in mind that force is a vector. You can have negative force. Weight is defined using the normal force that the earth exerts on you due to gravity pointing down. There is the negative force of gravity and the positive normal force acting on you to determine your weight.

What does this have to do with torque? The reason you can apply force to a lever arm and not experience motion, for example when trying to loosen a bolt or a nut that is on tight, is because there is a negative frictional force opposing the centripetal force you are creating.

To calculate torque you have to factor in the NET force in one direction (centripetal force minus frictional force). Therefore, you have to overcome static friction in order to apply a net positive force and create torque.

If you have force you have to have movement UNLESS there is another force acting on it in the opposite direction to prevent movement.

I'm sorry i guess if the dictionary says tends then there must be a situation where you can have torque but no movement. I'll be removing two eggs from my face. But I spent a while thinking that over and can't see a reason why you can't have negative torque if you can have negative force? I haven't ever heard of negative torque though. If you do a google search, however, you get some results for negative torque.

If I made any other mistakes please point them out but I do believe the rest is accurate.

I think many of the posts here are way too hung up on component weight in their analysis of torque. The engine's power comes from burning fuel, not the inertia of the spinning engine parts. Power is not torque, but in steady-state mesurements (a brake dyno measuring torque at a single RPM), I would think that component weight would have little to no effect on torque. In dynamic measurements, like a chassis dyno, it is clear that heavier parts (like a heavy flywheel) give lower HP and torque measurements.

Maybe this is a confusion of cause and effect. Torquey engines tend to have a lot of rotational inertia because they have a large displacement and/or long stroke. Engines that rev high need to have light parts and short strokes to stay together. Those high-revvers tend to have less low end torque than low-revvers with similar power. But that doesn't mean that a lot of rotational inertia creates torque, but rather torquey engines tend to have a lot of rotational inertia mainly by coincidence (don't need to be light, tend to have long stroke and large displacement).

The 13B ingests the same amount of air per main shaft rotation as a 2.6L piston engine, so I think that size is the closest equivalent to the 13B from the piston world. So the "it's only 1.3L" excuse for the low torque is not a very good one -- though "it's only 2.6L" isn't such a bad excuse. :) The 13B is a small engine compared to the V6s that are in competitive cars. But there are engines with similar displacements that make more torque than the 13B. I think the explanation there is that the 13B has a small effective "stroke".

There are some very nice things about the 13B that perhaps make up for the lack of low-end grunt. It has a nice light rotating assembly, which to me feels a whole lot better than engines with a lot of rotating inertia. The 13B also revs high and makes very good power for it's weight or displacement (however you wish to rate it). It is delightfully smooth due to the inherently balanced 2-rotor engine design. The torque curve is very wide (compare it to similarly sized piston engines), even through it isn't very tall.

The best engine in the world would have lots of power, tons of torque, zero rotational inertia, and low static weight. Good mileage would be nice, too, but you've got to compromise some things. :)

-Max

But that doesn't mean that a lot of rotational inertia creates torque

If inertia is a component of torque then how can you say that?

It is a fact that if you increase an object's inertia you increase the torque.

So, increasing the mass of the crankshaft and its radius then it should mean that its torque would also have to increase.

I also never said the engine's power came from inertia.

Stroke plays a part in torque that is true. The longer the stroke, the greater the distance from the axis of crank rotation, and the more the torque produced. Long-stroke engines make more torque at lower rpm than shorter stroke ones.

ON HALF OF THE ROTATION THE INERTIA IS IN THE OPPOSITE DIRECTION RIGHT? SO isn't the increase offset somewhat but the "negative" inertia- on a piston engine?

Whoa inertia isn't a vector you can't have negative inertia. It's just the property of an object (crankshaft) to resist motion. Mass and the radius.

what i mean is that if evrything had more mass then on the down stroke of the piston you would have more to push down with but on the way back up you would have more to push up negating some of the benefit you had from the extra force on the way down.

Originally posted by GooOnYou
It is a fact that if you increase an object's inertia you increase the torque.

So, increasing the mass of the crankshaft and its radius then it should mean that its torque would also have to increase.
This is true exept that the increase in torque is not positive in this case. The more inertia the rotating assembly has, the more torque it requires to be able to move; so we have less available to use.

Whoa inertia isn't a vector you can't have negative inertia. It's just the property of an object (crankshaft) to resist motion. Mass and the radius.

Exactly, the property of an object to resist motion, the more mass the more resistance to motion.

Originally posted by GooOnYou
If inertia is a component of torque then how can you say that?



Think about measuring torque at a single RPM (like on a brake dyno). The crankshaft is not accelerating rotationally (RPMs are fixed). That means it's rotational inertia is out of the picture. What you are left with is the force of the expanding gasses pushing on the pistons or rotors to produce the torque. This is a bit theoretical since I don't think you could actually keep an engine at some precisely unvarying rotational speed, but I think the idea is still valid so it is a useful thing to imagine.

In the dynamic sitatution, like accelerating on an inertial chassis dyno, having a lot of rotational inertia actually hurts you. Since you are accelerating the crankshaft rotationally (i.e. revving it up), some of the engine's torque will be spent accelerating the crankshaft itself. The more torque required to accelerate the crankshaft, the less you will have to accelerate the dyno drum. A heavier crankshaft will result in lower measurements of power and torque. In reality, the difference will likely be small here since you dyno in higher gears and you aren't really accelerating the engine internals that quickly. But I once did some calcs on the effects of switching to a light flywheel and the numbers in 1st gear are surprisingly large: 50HP-ish for the particular car I was calculating for (it will vary from car to car). The differences dropped off to 15-5-3-2 or something like that for the higher gears. You only get a big difference when you are revving the engine up quickly (like 1st gear in a light, powerful car).

-Max

I think I see what your getting at and its true if you have a heavier crankshaft, it will be harder to rotate and the angular acceleration will be less but torque may or may not suffer because inertia is increased as well, but if you have no inertia then you can't have torque. If there is no force being applied to the crankshaft then there is no torque at the crank.

You can't have torque either if there is no circular "twisting" motion. What we have been discussing is possible ways to increase/decrease torque on the crankshaft and the difference between how torque is created in piston engines vs. rotory engines.

Inertia is completly independent of acceleration or any motion. Any object has a moment of inertia moving or not.

This is true exept that the increase in torque is not positive in this case. The more inertia the rotating assembly has, the more torque it requires to be able to move; so we have less available to use.

The pistons/rotors are a means of creating torque on the crankshaft. I think maybe you meant the more inertia a rotating assembly has, the more angular acceleration/force it requires to be able to move. This is true and there is definately a delicate balance between the amount of force the pistons/rotors exert on the crank and the moment of inertia of the crank itself to produce max torque. You can't have an inertialess crankshaft nor can you have a crankshaft that is too bulky to spin. There are also other ways of increasing inertia without increasing mass.

Most of what I'm talking about is theoretical and just possible factors that could lead to the reason why the rotory has less torque than the piston engine. If you increase the inertia, torque should increase at the same angular acceleration but by increasing the mass of the crankshaft in order to increase inertia, angular acceleration suffers. Its a paradox, but if you could get the same force acting on the crankshaft through some sort of rod at a farther distance from the center of mass of the crankshaft then you could increase torque significantly. The best example of this is when changing your lug nuts, to get max torque and make it easier to turn the lugs, it is best to use a really long wrench to get the most leverage and torque. By increasing the length of the wrench, you increase the moment of inertia of the system which is the reason why the longer wrench creates more torque. It further increases torque if you apply the force perpendicular to the direction that the wrench is sticking off the lug nut.

I believe the lack of connecting rods in the rotory play a big part. They act as a "longer wrench" when trying to tighten a lug nut (same example I used earlier). They provide more leverage and increase the moment of inertia of the crankshaft without increasing the mass of the crankshaft.

what i mean is that if evrything had more mass then on the down stroke of the piston you would have more to push down with but on the way back up you would have more to push up negating some of the benefit you had from the extra force on the way down.

I'm not completely sure what you mean here but I think you are trying to make basically the same point as neif. First of all it definately isn't a good idea to increase the mass of everything. It probably isn't even a good idea to increase the mass of the crankshaft because that would lead to a decrease in the angular acceleration and overall decrease of the force acting on the crankshaft as I discussed earlier.

The only force acting on the crankshaft from a piston engine occurs through the connecting rod on the down stroke. On the way back up, you have to overcome gravity which is almost negligable because the force of the piston is so great and that force continues through on the up stroke (Conservation of momentum and what not). So you do lose some of the benefit but I don't think it is enough of a loss to matter much.

I'm sorry if i repeat myself or ramble on. I probably made a mistake somewhere in this post, please feel free to ask more questions and point out anything you think could be a flaw in my logic. I'm not too good with words but I think we have all learned something through this thread. I know I have.

Here's an article from a circle track site that mentions the effect of crankshaft weight on the torque production of an engine:
http://www.circletrack.com/techarticles/84199/

-Max

Nice article

Wow - there seems to be lots of bad info zoom zooming around here.

The inertia of components does nothing to make torque - its only effect would be to average out torque fluctuations.

You can have lots of torque with no "movement". In fact a steam engine produces it's maximum available torque at 0 RPM.

Torque and Horsepower are directly tied to each other. You can't have one without the other.

Torque is a measure of force - in a rotational sort of way (the leverage example)

Power is a measure of the RATE of doing WORK.

All of the below are ALL related, and changine one will affect the others:

Power, Torque, Mass, Acelleration, Time, Distance.

And to try to keep my post short - Power is the thing that makes the most sense to us car folk when we talk about performance. When our car is acellerating hard, it is really power we are feeling. Power is a product of torque. What matters to us is how quickly more torque is available.

I'll bow out of this argument before I get too involved. I have seen it on other forums as well. Same ol' same ol'.

My parting comment is to think about this:

A Tractor produces an absolute bucket load of torque. Much more than the '8. Will it beat the '8 in an accelleration run? Not likely.

Cheers,
Hymee.

PS - Has anyone here been to, or seen, a Tractor Pull competition? It is a great experience to help visualise torque and force.

:D:D:D

thanks Hymee, this thread is annoying.

The inertia of components does nothing to make torque

This is wrong there can be no torque without inertia.
If torque and distance and mass are related and inertia is derived from the mass and distance from the center of mass of an object to the tangent force acting on it then it has to be related to torque as well.

The article maxcooper posted explains a lot.

its only effect would be to average out torque fluctuations

I'm not too sure what this means. Please elaborate. :confused:

You can have lots of torque with no "movement"

This is true, I realize now. Possibly due to negative torque created from negative force pushing the opposite direction such as friction when trying to loosen a lug nut that won't budge.

Torque and Horsepower are directly tied to each other

This is also true but we haven't been discussing horsepower, power, or torque. Horsepower is definately the key to winning races. The yawpower article posted earlier has a lot of good info on that.

It may be that a lot of people think what I am talking about is totally off the wall and "bad info" but I want people to challenge it and not take what I say as fact so we can all learn a little bit more.

I've never seen a tractor pull but it sounds cool :D

Originally posted by wakeech
thanks Hymee, this thread is annoying.

JUMP IN AND HELP OUT ANYTIME YOU WANT WAKEECH

hymee and the others seemed to have missed the point- the point was how do the engines make T, what could cause an increase or decrease in T, and why does a rotary make less in comparison to a piston version.

Originally posted by GooOnYou
This is wrong there can be no torque without inertia.

That's true by coincidence, since you have to have some physical body (e.g. crankshaft) to exert a twisting force and thus you have some inertia by virtue of haing that physical body. But that does not mean that having a crankshaft with a large moment of inertia (= amount of rotational inertia) will increase torque output versus a "lighter" crankshaft. "The inertia of components does nothing to make torque." Both of your statements are true, and they are not in conflict with each other.

The basic point is that the rotational inertia of the crankshaft (or eccentric shaft) has nothing to do with how much torque an engine makes. Having a relatively "light" main shaft is not one of the causal reasons the 13B lacks low-end torque. The engine would have more torque if it was a 3 rotor or had greater eccentricity (stroke). And the shaft would likely be heavier in those cases, but the increased weight of the shaft would not be the cause of the torque increase. Rather, it is just another side effect of the change in configuration (another rotor or longer stroke).

As far as smoothing out the fluctuations, a heavy rotating assembly resists changes in speed (RPM) more than a light one. A shaft spinning at 3000 RPM wants to stay spinning at 3000 RPM -- it doesn't want to speed up or slow down. Over the course of one rotation of the crankshaft, the amount of torque produced by the engine varies. Consider a single cylinder 4-stroke engine -- the power stroke is only 25% of the complete cycle (180 degrees over two rotations of the main shaft). The output shaft will speed up during the power stroke and will slow down the rest of the time. And even during the power stroke, the amount of pressure exerted on the piston by the expanding gasses and the leverage of the connecting rod and crankshaft will vary, which makes the torque fluctuate. Having a large flywheel or simply a lot of rotational inertia in the crankshaft will reduce the amplitude of the fluctuations in shaft speed. The output will be smoother (less noticable power pulses) when the moment of inertia of the rotating assembly is large.

-Max

Originally posted by zoom44
JUMP IN AND HELP OUT ANYTIME YOU WANT WAKEECH

...thing is, i don't wanna. it's kinda funny to see what some people have to say.

...and max is on the right track. inertia (i think this is an american word meaning "mass") has nothing to do with how much torque is produced. i've already covered the basics as far as why rotaries don't make so much torque.

Originally posted by GooOnYou
This is wrong there can be no torque without inertia.

Boy, have you got your fundamentals mixed up! :(

Read that circle track article again - it's diametrically opposed to what you're claiming. You suggest that more inertia (via heavier engine components) makes more torque - that's wrong. From the article:From a practical standpoint, acceleration of a “heavy” crankshaft absorbs more torque than one of less weight, thereby reducing the amount of net torque available to accelerate the car. (Note also that the article is referenced mostly towards balancing.)

My mechanical engineering and internal combustion engines training is over 20 years old now, but still - torque requires no movement nor inertia. There definitely exists static torque - force times distance, that's all. As mentioned, steam engines and electric motors make maximum torque at zero rpm. If you introduce time as a factor, then you're talking power, not torque. Re inertia - unless you're changing the speed of rotation, it's a complete non-issue. It is entirely possible with an engine dyno to keep rpm constant and vary load and throttle opening - so, for example, you have a test bench engine running at 3000 rpm, at 20% throttle. Say it's producing 50 lb-ft of torque. Open the throttle to 100%, increase the load to keep the rpm at 3000 - there is absolutely zero change in inertia since the rpm didn't change, correct? How come the torque output increased to 200 lb-ft then? Because inertia is NOT a factor in torque at all.

Here's another example to consider - take a V8 with heavy steel rods and cast pistons, real slugs. Put it on a test bench and measure torque at, say, 3000 rpm and full throttle. Now rebuild that same engine with titanium rods and forged aluminum pistons that are otherwise identical (same crown shape and compression ratio), and rebalance the crankshaft for these, so the crank counterweights will be lighter as well. Much lighter engine internals - put the engine back on the test bench and measure the full throttle torque at 3000 rpm - according to your theory, it should make less torque. However, you'd find that the torque would be exactly the same. Also, the lighter internals engine would accelerate much quicker due to the lower inertia. In performance engines, lower inertia is always better.

Regards,
Gordon

This is a little off topic, but I replaced my engine with three gerbils on crack running around endlessly on a wheel, attached to my drive shaft...No matter how many times I shock their little balls with my cattle prod, the car will not move,

Do you think reduction gears will help? Is anyone making a hamster mod?

are you sure you're not holding that cattle prod backwards and trying to think and chew gum while typing?? ;)

No, I have been drivin mad by

1 A inflamation of my right eye which is very painful and has left me half blind

2: The pain meds for the above

3: The toe on my right foot that I fractured on tuesday when I triped over a toe that my kids left on the floor, and I could not see due to my damaged eye

4: The poopy diaper I had to change when my baby had a massive blowout

5: Yet anothet thread whining about MPG/MPH/HP/DYNOS/car x is better...

6:the strange photoshoped combo of you and a dog ...truly disturbing

Sorry for bringing this back guys. I notice a lot of differant opinions on this subject. I'm trying to understand this the best I can. So instead of us comparing the rotarys torque to a piston, why not compare the torque of the Renesis to the 13b found in the 3rd gen Rx7?

I understand that one is turbo charged while the other is NA but if the Rx7 has 255hp and 217 lbs why does the NA Renesis with 238hp have a torque peak of only 158? I mean both engines have the same displacement, similar rotating masses(Renesis is slightly lighter because of the lighter rotors for higher rpm's) and produce similar amounts of hp. Why is the torque of the Renesis so much lower by comparison? Does it come down to the 50% larger exhaust port area of the Renesis? I ask because I've always heard that some exhaust back pressure will add torque. Thats why we Fd guys tend to loss some low-end when replacing a cat with a midpipe. To add to this....look at the 20b of the Cosmo. That engine was tuned for torque because in stock form it had more restrictive exhaust sleeves. With these sleeves in place, the engine would produce higher torque figures than hp figures but if the engine was ported in the exhaust area that engine would also loose some torque. Someone help me out hear so I can feel more educated.

Originally posted by T-von
Why is the torque of the Renesis so much lower by comparison? Does it come down to the 50% larger exhaust port area of the Renesis? I ask because I've always heard that some exhaust back pressure will add torque.

again, my first post.

force = pressure * area. the 13BREW's air/fuel charge is almost double what the 13B-MSP's is because of all that mechanical compression (the turbos). so even though the compression ratio is lower, the amount of pop is understanably higher.

their horsepower outputs are still fairly close because, as in my first post, at maximum output they're still burning about the same amount of air and fuel, just in different ways.

the internal mass of the componentry has nothing to do with how much torque is being made. i have no idea where this stuff is coming from.

There's also the difference in redlines
3rd gen is lower and since torque and hp are related by rpm this accounts for part of it.

Peak horspower is similar between the two engines but the average power is much higher in the 13B-REW. The torque peak listed is not at the horsepower peak. It is lower in the rpm range. since horsepower and torque are mathematically related, you can't have more of one without more of the other. Since the 13B has more average horsepower, it also has more average torque hence the higher published torque specification.

Ok now things are starting to make since. Thx for the replys guys. Now what about the 20b with the more restrictive exhaust sleeves adding additional low end torque?

To give you guys an example a fellow forum member on the Rx7club forum has a rebuilt stock block 20b in his convertable w/nonsegential twins making about 370rwhp and over 400 lbs of torque. Yes you read that right... the torque is actually higher than the hp. By comparison the Pettit Banzai makes 550 crank hp with more boost, a ported engine, nonsequetial twins, and less restrictive 13b exhaust sleeves. The pettit engine only makes 450lbs(less torque than hp). Overall the Pettit engine is built to flow more air as compared to the engine in the convertable. Now I was told by the 20b guys that the more restrictive exhaust sleeves adds additional low end torque to the 20b. This would explain why the higher flowing Pettit engine with less restrictive 13b exhaust sleeves makes less torque than hp. Also I have noticed that rotary engines in general that have excessive intake & exhaust porting will loose more low end torque(pp , bridge, ect). This made me think about the Renesis. Mazda engineered the engine to flow really well with it's larger than normal porting, porting so large that there is really no additional room to port any furthur. This added flow of the Renesis makes me think of it as a high flowing bridge port that has no lowend. Now since more restrictive exhaust sleeves will increase the low end torque of a 20b, couldn't the Renesis be engineerd to have a mechanical restriction to give the same benefits of increased low end?

By restricting the exhaust ports, you will be reducing the rpm range.

Like wakeech said above: F= Pressure * Area

The pressure comes from the air fuel mixture being ignited and the area is the size of the combustion chamber. The reason for the low torque is due in part to the 3:1 torque reduction between the ecentric shaft and rotor , the small displacement, and the large cumbustion area (relative to a cyclinder engine).

So if you want to increase the torque...increase the bang. This means either through forced induction or increasing displacement.

If the 20B's peak torque number is greater than the horsepower number, the torque peak has to be somewhere below 5252 rpm. Above this point you can not have a higher torque number than horsepower. The engine is obviously built for low end power and this is obvious with only 370 rwhp. I'll bet the dyno chart is killer in the low to midrange but falls on its face up top. Sounds like way too small of a turbo for the airflow requirements.

Turbo engines do some very different things in regards to port sizes. It is very likely that the stock lousy exhaust sleeves on the 20B all cumulatively flow more than the turbo being used on that engine. If that is the case then the turbo and not the sleeves are the restriction. The turbo needs to be changed and those numbers will go up on the top end. Yes the low end will decrease. There is always a tradeoff.

Originally posted by AbusiveWombat
By restricting the exhaust ports, you will be reducing the rpm range.



Not necessarily I'll explain my idea here in a sec.


Rotarygod, you are very right about the turbos being non efficiant for higher flow. This is the main reason most people ditch the twins and install a single on a 20b. Remember, I'm talking about the 20b's more restrictive exhaust sleeves adding more low end. Both of these engines have the same factory twin turbos running non sequecially. The main differance is that the Pettit engine breaths better with it's additional porting. The non ported engine does fall on it's face in the higher rpms but, the Pettit engine doesn't. With the additional flow of the ported engine yes the tradeoff is less torque like you already mentioned. But the fact is that the engine with the more restrictive sleeves does have more low end.

Overall my theory is, if you could engineer a mechanical restriction in the exhaust( like the more restrictive exhaust sleeves) you could very well increase the low-end of the Renesis. AbusiveWombat here's my explanation of how that could be engineered so it wouldn't decrease the rpm range.

The Renesis has 4 exhaust ports(two on the outer plates and two in the intermidiate plate) The mechanical restriction could simply be a wastegate style accuator flapper door that closes off the 2 center exhaust ports of the intermidiate plate. This would effectively cut the exhaust ports area in half and divert the exhaust gases to the outer exhaust ports therefore creating the restriction. This actuator (controlled by the ecu) could be programed to open at a specific rpm(lets say 3k rpms as an example). Once 3k hits, the door would start to open to free the restiction. This way the Renesis performs as normal in the mid and upper rpm's but hopefully with the added benefit of more low end.

Overall does this make any since to you guys? Or an I just crazy?:D

just crazy!

j/k :D

The Renesis is unique in that while there are 2 exhaust ports in each rotor housing of the engine itself, there are only 3 ports leaving the engine. The 2 center ports are siamesed. This is where tuning problems come from. If you closed off the center port, the gasses would transfer back and forth a little between rotors messing things up a little. you'd have to open the ports by about 3500 rpm or so but this could be a theoretical way of improving things. Piston engine cars that vary the exhaust timing in addition to the intake timing are in essence doing something very similar to this.

The issue with both of those 20B's isn't really so much the sleeves but the size of the porting done. The factory rotary sleeves actually expand in area by about 100% over a distance of less than 2". If the sleeve is larger than the port opening in the engine, the problem can't be insufficient sleeve sizing. I have some custom machined exhaust sleeves on my 13B that maintain the area of the engine ports all the way to the header. The ports are just about as large as I can get them but the exhaust tubing is only 1 3/4" in size. This is far less than many people use on the stock ports. There is more flow but my sleeves have less area than the stock ones. The issue will be with how big the porting is on each. I do admit that the stock sleeves are very restrictive on the 20B only due to their strange shape but it has nothing to do with their area. There is just alot of turbulence that is holding everything back.

The last thing you want is restriction or backpressure. You never want these and they will never help you anywhere. The technicallity that confuses everyone is that you do not want to exceed the flow requirements for a particular rpm. The goal is to have max flow along with max airflow velocity. That is where the key is. Just making a hole larger may not neccessarily help even though it flows more air. If velocity is too low it hurts. This is what happens with the factory exhaust sleeves of the older rotaries. They expand in area and everyone uses these 2" and larger pipes that are totally worthless saying the pipes flow better. This may be true but the engine ports can not flow that much so what is the point? What you are getting to is really finding a way to optimize flow per rpm and this is a good idea.

In a perfect world your intake and exhaust systems would work the exact same but in reverse from each other. Each one would start out as long and skinny. As rpms rise they would become larger in area while they also got shorter. They would be infinitely variable to accomplish this. The port timing in the engine would also do the same thing. The ports would start out as having less duration and being small and then as rpms rise they would get larger and their timing would continuously change. Our ignition systems would vary the timing constantly depending on port timing, intake length, and load and our fuel systems would be direct injection and also adjust accordingly. Too bad we don't live in a perfect world!

Ok well if closing of the center exhaust ports doesn't work, how about putting and electric exhaust cutout after the manifold that is slightly open and then the ecu fully opens it at a specific rpm? This would be like a shutter valve inside the exhaust piping. This would be the same principal as my other idea. I'm not trying to beat a dead horse but I hear to often that some restriction/backpressure is good for low end but terrible for top end. This is why when the Fd guys put on midpipes they loose some low end because of the less restriction of the cat. I would hope my idea would give you the benefits of both on the Renesis.

Those custom exhaust sleeves you have..... I think I've seen those before on the Rx7forum. Are you the one that posted info about these over their? If my memory serves me correctly, the sleeves are suppose to smooth out the turbulance the factory sleeves cause which in turn keep the exhaust velocity high to help spool a larger turbo very quicky. These are the ones that need the custom manifolds that are shaped just like the exhaust sleeves outlets that go out 3" before turning right?

Yep those are mine!

You are comparing a turbo car with a nonturbo car as far as exhaust effects are concerned. On a turbo car, the small restriction after the turbo causes a small boost rise. This is because it takes more effort which is shown as a greater air/fuel mixture to force it's way through this restriction. When this happens the turbo gets hit with more energy and starts to spin. The sooner it starts to make boost, the sooner it will hit max boost. However this same restriction on the turbo engine is limiting the total output of the engine. There is a general rule that actually has many acceptions to it that states that for every 1 psi of exhaust backpressure, it takes 2 psi of boost pressure to cancel it out. Yes there are exceptions. Basically the restriction will cause a sharper boost rise on the low end be be a big restriction up top. For total power on a turbo car, no exhaust is the best exhaust but it may lag a little more. Again there are always exceptions.

The Renesis is not going to get this same effect since it has no turbo. A restriction is just a restriction. The key is in keeping exhaust gasses flowing fast enough in the smallest space possible with the least amount of turbulence. You are on to a good way of thinking though but the reasoning is not the same as on turbo cars.

T-von - The low end of the Renesis can only be cured through forced induction or increased displacement. Since increasing displacement is a PITA, you're basically left with forced induction. Playing with exhaust restrictions may yield a few ft-lbs of torque but will not be very significant. And certainly not enough to warrent all the time and effort put into designing and fabricating a fancy valve system.

Now everything really makes since. I never thought turbos made that much differance. Thx for the education lesson guys:) . To bad I guess my idea will go to the scrap heap.:(

holy S***

That was like the most in dept thread I have ever read...

Seriously you guys are crazy!

I think I should go take a nap before my head explodes...

I have an allmighty torque headache .OUCH :D

So much to learn in so little time .

cheers
michael

All of these back from the dead threads are suddenly showing up lately.

yeah, but it's goood 'cause that means people are searching.

thanks guys.