Let's examine how ram air is different from other systems
 

Once again I feel compelled to write something. This one is about the myths of ram air and the effects of intake tuning in general.

There are many ways to get air into an engine. The easiest way is to just slap a filter on it and let it suck it in by itself. This is the most common method. As we all know, the more air we get into the engine, the more fuel we can add, and the more power we can get. This is the basis for forced induction. Unfortunately forced induction requires that a little bit of power be robbed from the engine to make more. Since we still come out ahead in the long run, this is acceptable. Obviously there are some systems that are more efficient than others. The goal of everyone of them remains the same though. More air is more power.

There is more to making power than just giving the engine the required amount of air. There are also other ways to increase output. The length of the intake runners makes a huge difference in where the engine makes the most power. Shorter runners make better high rpm power. Longer runners make better low rpm power. This is because of pressure waves inside the manifold being timed to help add more air to the engine just before the ports close. In a sense this is ram air. However this is not ram air in the context that I am going to focus on right now.

In a ram air intake system, air is supposedly channeled straight from the front of the car and into the engine. This high speed air supposedly forces more of itself into your engine and gives you a gain in power. Can this actually work? Yes and no. It depends how it is done.

Most systems out on the market today are "cold air". The don't so much ram air into the engine as they do just send cold air to it. By cold air I mean air from outside that is colder than the hot engine bay air. Colder air is denser air and denser air is more air. This doesn't mean it is ram air though. Let's get a little technical for a minute.

The rotary as we all know doesn't flow the same amount of air as a 1.3 liter engine. It is closer to a 2.6 liter engine interms of size but it still flows more air than this. for everything to work properly, we have to size it's airflow at almost 4 liters. That's alot more than 1.3. Since we really want our intake air to be going no faster than 180 ft/sec. through the throttlebody we need to figure out how much flow that is at max rpm. In the case of the Renesis it is about 9500 rpm. At 9500 rpm this would be about a 3" inlet pipe. It would be close. The throttlebody on the RX-8 is a little smaller than this though. Just for argument sake, we'll stick with the 3" number.

If a we were at 9500 rpm, we would need to be moving at 180 ft/sec or about 123 mph just to make the forward velocity of the vehicle the same as the airflow into the engine. You'd have to go a whole lot faster to get any usable gain as this is only the break even spot. Obviously we would be at a lower rpm at 123 mph than this so we should have more air entering the engine through ram air right? Not necessarily. If we were to put our air filter straight into the path of the outside incoming air, we still wouldn't get a ram air effect. The 3" inlet pipe is not going to take in hardly any more air. The reason is that as air is trying to force or ram itself into this pipe, it is doing so in a very small space. Maybe a little more will get in, but you won't really notice it. Luckily there is a way to get around this.

Let's say we used a 6" diameter pipe that faced forwards into the airstream. We can't just taper this down into a 3" pipe since the added air will just reverse itself. We'd actually get less air into the engine this way since we'd have to speed the air up as it enters the pipe. when we speed the air up, we lower it's pressure. That is not the goal. Less pressure is less air. If we feed the 6" pipe into an airbox or plenum chamber, we can alleviate this problem. We then feed the 3" pipe to the engine into this. The 6" inlet pipe has 4 times the area of the 3" pipe. When we bring all of this air into the airbox, the greater area or the airbox forces the air to slow down. When we slow air down, we increase it's pressure. This may confuse you when it comes to turbochargers or superchargers but I assure you this is what is happening in them too. The exception to this is the roots blower. It doesn't compress the air by slowing it down. It speeds it up and causes it to build up in the intake manifold. This is where the pressure is increased.

Back on topic. This airbox is now pressurized to some extent. Don't expect gains of supercharger proportions though. This higher pressure air is what the 3" pipe to the engine is feeding off of. Suddenly we have higher than ambient pressure entering the engine. We call this boost! Now we are ramming air into the engine. In order to utilize ram air, we must find a collection point for the air where it can build pressure. If you just have a filter in the airstream, you don't have this.

Racing Beat found that on their 1st generation Bonneville RX-7, a true functional ram air system added 3 mph to the top speed of the car. That doesn't sound like much but at 180 mph, it takes alot of power to go a little faster. This should still emphasize the fact though that you are not going to get incredible results from ram air. It is alot of effort for a little gain. If we could get even 1 psi of extra air into the engine, on a 200 hp engine that is still around 13 hp more. This is only at high speeds but it is more than you have now. If you find old pictures of the Racing Beat 1st gen. you will notice that there is a single 6" pipe that is fed air from the front of the car. It also dumps into a large plenum chamber in front of the throttlebody.

Next time you see a product that is marketed as "ram air" ask yourself, is it really?

Do any TRUE ram air systems existyet for the Rx8?

just the one that came on the car:) ^^

What do you do for a living man? This is a great write up....

Thankx for the info. I have never seen you so enthused about an intake before as you are with Racing Beats.. They must have a great idea on their hands for you to endorse it.

Hehe. Simple thermodynamics. Good write-up rotarygod.

Basically, increased pressure leads to a higher mass air flow rate, which means more power.

Come back to UH and teach Thermo II.

Very technical and makes for a good read Rotarygod.
Unfortunately the ricers out there won't be able to comprehend it and will still believe what the marketing department tell them.

the other thing about "ram air" bullshit is that when you're actually trying to create a very high pressure point on the front of the car, you're in essence enhancing the drag your vehicle has through the air. at the kinds of velocities you're talking about, this is probably the absolute least efficient way to make horsepower (which is at the same time costing you an awful lot of energy to continue to push the car through the air) even at best.

besides, when you're making a serious amount of horsepower (like RG is talking about here, it's like 200... what about 400?? or 600?? or 2200??), this is a fool's game. ram air is bullshit.

When are you putting together all you material and submitting to an editorial?

I'm a real estate agent.

This was actually written so the mass marketed ricer bs doesn't make it way here successfully. It wasn't intended to promote the Racing Beat intake. I mentioned them because they did this on the Bonneville cars and proved it works.

Saying that however, their new system I do believe to be the best out there. After visiting Racing Beat, meeting the people, and seeing how they test things, I have nothing but confidence in them and their abilities. They are some of the most honest people out there and don't lie to people with large claims. They are realistic in their claims whether it's what the public wants to hear or not. You've got to respect that. Remember it is numbers not real world results that sell product. They give you real world results at the risk of hurting sales. I'll take honesty any day! This new intake system of theirs is very nice and very well designed. Your car will not be loud and will not idle rough either! This shows proper engineering rather than just slapping a filter on a tube. Although I speak against them frequently, I'm not entirely against cone filters. I am against the way most people utilize them in kits though.

I'm sure there are alot of aftermarket people and companies that wish I would go away. :D

Great detailed write-up as always RG... thanks!

RG: I could conclude, (based on what you stated), that changing out my stock airbox and putting in a k&n typhoon intake system in all could have decreased the hp of my engine, because there is no longer a box to build pressure in?

Thanks for the info

At the very least, you are not fully protected from hot engine bay air, even with their heat shield, the inside of the air filter does not have a nice smooth radius like the stock intake box does, and your intake tube after the filter is too long. Otherwise it's fine! The stock airbox doesn't work as a ram air box. It does tune the intake though and this offsets the purely flow based cone systems out there. Wait until the world finds out that some of the aftermarket exhaust systems out there actually make less horsepower than the stock one!

ouch! I'll be pretty dissapointed because I have a B&B racepipe (love the extreme sound of the rotary) and the B&B catback, have yet to dyno it. I do notice a power loss at lower rpms because opening the exhaust up and releasing some backpressure caused the loss of whatever torque I had. I do feel a difference though when I'm up at 7-8500 rpms, or it could be in my head.

Not all lose power over stock. Not all gain though. The race pipe will definitely give you a gain though.

Oh ok thanks for a minute there I thought that I was just imagining things, and that all the "fun" I had putting it in was a waste. Thanks for the info.

Thanks rotarygod -- as always, exceptionally educational for me. And much better written, too; the spacing makes it much easier to read.

I know we have the stickies, but I think we should highlight and collect some of the key posts such as this one as some sort of definitive collection somewhere on the site. This way, if someone wants to look up intake engineering and physics, he can just check out the section on intakes and find a couple of key posts, rather than filtering through the search function sometimes hopelessly.

Maybe even come up with a rec system?

no, backpressure is bad, you don't lose low end horsepower because you have less backpressure (in any system, ever, under any circumstance).

You lose power because you have too much flow not too little backpressure.

I got the point of this thread, and entirely agree with it. However, I have two questions (No2 might feel like "deja-vu"!):

1) Why are you comparing the Renesis air flow requirement as a 4L engine, whereas we know it breathes more like a 2.6L? Or do you mean that a 2.6L engine running at 9000 rpm can be compared, in term of air consumption, with a 4.0L engine running at 6000 rpm?

2) Please explain this : "we really want our intake air to be going no faster than 180 ft/sec. through the throttlebody". Why??

Thanks,

IKN

I was saying that you loose torque with an open exhaust I just phrased it wrong. But I also thought that a lose of power on the low end was a cause of less back pressure when freeing up an exhaust system, maybe I was getting something confused.

more good info from the g man, will an intake by itself help out at all or does it require an exhaust system etc. to make any use of it. I'm just curious, my guess is that it won't do a whole lot until you aid the fow with a better breathing exhaust but for those of us that can't really spend a lot at a time what would be the better first choice?

not especially. and i don't know what RG is saying about "too much flow", it's too little flow through a path which is oversized for the application. if the speed is too low, the static pressure builds and what you end up with is a lower pressure diffference across the exhaust system, effectively raising your 'backpressure' (when in fact i believe backpressure is the static pressure of the system, so the reading would actually drop with the lower velocity). brounelli's law, and all that.

and just fyi (since this is an educational thread) torque as you describe it isn't the "torque" at all, but just low end horsepower (the same as high end horsepower), and yes, this motor doesn't make as much horsepower off idle as a much larger engine would (duh). without significantly changing the characteristics of the engine's function, you don't actually lose any low end horsepower (and with a more efficient exhaust system might even gain a couple of joules), it's basically the butt dyno placebo effect.

IKN, the 180ft/sec number is an arbitrary number chosen by Corky Bell as a good number to try and keep intake velocities close to as a maximum (as in, 182 or 185 would still be ok as a maximum if you knew what was going on, but 210 is obviously not) because of usual observable build up of a boundary layer in velocity stacks with a polished surface, which of course at that point is beginning to hinder the movement of your air charge rather than enhance it. if you were doing some tricky things like beautifully scoring your intake tract with intersecting spirals, or some slight dimpling, or any of that sort of thing, you could concievably get velocities even closer to theoretical (at the same limit of force (pressure difference times area acted on) you get more air moving, so higher than his 180 number but without changing anything else to increase that velocity).

oh don't worry about that overgeneralised hooey, "more air in means more gas out", please.

no, your motor is still moving about the same amount in and out (unless you're actually changing the mechanical properties of the system with a priniciple like ram air, which in this thread has been all but defeated as something which isn't of merit) and using things like 'less restrictive' intakes and exhausts only 'add' power by allowing the motor to move gasses in and out with less energy (increased efficiency). so you have this left over energy which can me used to motivate the vehicle instead of the gasses in and out of the motor.

so, if that's all it is you're doing, something of benefit on one side or the other is still going to make a difference on its own, and yes there would be even more benefit if they were 'working together'. i don't really think that one is better to do before the other.

Thanks for the breakdown Wakeech.

I'll have to say that I had the K&N on before I replaced the cat with a straight pipe and added the catback system. The car did idle rough when I put the K&N on alone. After adding the straight pipe and catback system, the idle seemed to run alot smoother unless of course I was running the car hard then the idle was giong nuts. I don't know if that is just all in my head as well or just a coincidence.

As we all know every time a rotary engine eccentric shaft rotates around a total of 2 times or 720 degrees, it fires 4 of our 6 chambers. This number is relevant because a traditional piston engine that we compare displacement to fires all of it's cylinders in 720 degrees. Since 2 chambers desplaces 1.3 liters, 4 chambers must displace 2.6 liters. You must also remember though that the entire intake, compression, ignition, exhaust cycle of the rotary is 50% longer than in a piston engine. We have over 50% more intake timing and 50% longer exhaust timing. This give us far longer to take in more air. When you run tesets on these engines, it appears that the rotary is very inefficient in how it uses air. The rotary actually takes 3 complete revolutions of the eccentric shaft to fire all of it's chambers which is 50% longer than a piston engine. All of these numbers add up to the 1.3, 2.6, 3.9 liter argument. Remember that each rotor overlaps the other one in terms of breathing. When the engine makes 2 complete revolutions, some air is still in the last 2 chambers since we don't have valves to close them off. When you combine all of these strange effects, the engine actually flow about the same amount of air as the larger displacement number we can give it which is 3.9 liters. I just round it up to 4 to make it easy. These engines move alot of air for their size.

In the past I would have said to buy an exhaust first. You can't take any mor air in if you can't get rid of it any faster. This also applies to engine with overlap and scavenging ability. If you have an exhaust that flows better, and you have some degree of overlap, during this overlap period you will get more air pulled in through the intake from the pressure change. A better flowing intake will aid this. The exhaust and the intake effect each other. However, the Renesis does not have any overlap. This is why exhausts and intakes aren't getting much in terms of a power increase. If we had overlap, we'd see larger gains. My vote still goes to the exhaust but in truth it really doesn't matter on this car.

In regards to the first part, I was saying the exact same thing you. Just reworded. Too little flow through a large pipe is the same as too much flow (area) for the required application and therefor too little velocity.

180 ft/sec actually isn't a Corky Bell number although he probably mentions it. It is a number in Helmholtz theory equations that dictate that you don't want air going through the main intake to be any faster than this. There is nothing wrong with flowing faster than this though. The intake runners themselves could actually see up to .6 mach or about 450 mph. Again that number comes from mathematical equations but they aren't Helmholtz based. I've got alot of big technical books with graphs of the effects of airspeed to efficiency lying around. It's pretty neat how these numbers all work out the way they do.

You will get a ram air effect if you get the air from a high pressure point on the car. In front of the windshield is one place. Some of the street pony cars and drag racers use this effect to boost the amount of air moving through the carburator. You can tell these cars by the air scoop opening to the rear of the hood.
This should work better on a EFI car. The computer would sence the amount of air moving through the system and increase the amount of fuel to compensate for the lean condition.

...but when you have a cowl in front of the windsheild you now no longer have a point of high pressure, not to mention it's all about the velocity that the air is being drawn in (where you have air being pulled into a hole faster than it can be pushed in you actually have a net negative pressure), etc etc etc.

this's all been covered. ram air is garbage.

thanks for the clarifications RG.

his thoughts do explain the designs of most IRL and CART cars with the ram air duct right above the drivers head....they however, are going 180mph + so I bet they get some benefit.

Interesting read regarding RAM air:
http://www.sportrider.com/tech/146_9508_ram/

I'd suggest that you should still do the calculations with a 2.6 l engine. The flow in the engine might be higher, but the Renesis engine probably also recirculates much more air or better exhaust gases than an ordinary piston engine (as you actually point out in that quote anyway).
Otherwise if it really were comparable to a 4.0 l engine at 9000 rpm it should be in the power range of a Corvette Z06 or run extremely lean or be extremely inefficient (and neither is really the case - although I'm sometimes not quite sure about the latter :) ).
After all any engine's power, be it a little 2 stroke, a gas turbine or a coal power plant equipped with a steam turbine, is proportional to the amount of oxygen it pumps and ultimately burns.

thanks for the input guys, I'll probably do exhaust first if my wallet ever decides to cooperate, good to know that either one would help out a little though :)

Actually you hit it. The engine is very inefficent. It wastes alot of air. Ask Richard Paul what he's learned about this.

So what's the best way to make it more efficient? :D

Maybe I am paraphrasing this incorrectly....but I think I read somewhere that any means of forced induction increase efficiency.

[Disclaimer: I'll delete the post if wrong...]

this is a quote of Rotarygod's post in why 1.3l

"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!"

just as an example a ferrari 360 modena has a bore and stroke of 3.34" and 3.11", these numbers make a big difference on an engine. Truck and econobox engines typically have a longer stroke, it's more efficient -- More time for the heat to move the piston. As opposed to an engine with a bigger bore and equal displacement. If you really care, look at how different engines of the same configuration and displacement with different bore vs stroke compare. Anyway, shorter stroke means higher revs are possible, bigger bore doesn't effect the revving ability as much. It's about piston speed more than the added weight of the bigger pistons, those things stop and go twice every revolution. Though there is more to it, rod ratios and such ... but my understanding of that is rather elementary

i think someone told me that shorter stroke engines are more efficient at higher revs ... though i'm not sure if it was in power to weight to fuel burned or whatever ... i think, she was just saying that they are more ideal than a longer stroke engine in that case.

Ok, so if it pumps a lot of air without burning it wouldn't this basically ask for a turbocharger to make it more efficient? So that the energy in that air flow would at least partly be regenerated?
Or a pressure wave supercharger (comprex) would do the same. After all Mazda has been using this concept on its Diesel engines.

Links regarding pressure wave supercharger:
http://archive.greenpeace.org/climat...7pressure.html
picture 1221: http://www.technolab.org/Hako/Katalog-e/Section9.htm
http://www.swissauto.com/uploadfiles/EN_200056.pdf

This would also mean that this is not the engine for a mechanical supercharger, since it would have to pump a lot of air for nothing.

Regarding a 'bigger bore short stroke engine' being more efficient at high revs (apart from the slower piston speed): I believe (as probably most of you too) it's partly because the valves, the intake and exhaust manifold have larger diameters and therefore there's less friction at high air speeds or high revs (which should also lead to a higher volumetric efficiency at high revs).

The rotary lends itself very well to turbocharging. You can use a very large exhaust wheel for better flow but still have great spool up times. The problem with thinking that the rotary would be better suited to a turbo over a supercharger based on efficiency is that you are assuming the engine uses disproportionately more air than it does without forced induction.

You're assuming that if we have more air that we aren't burning and therefore less efficiency, if we add more air, we burn more air. This is true but we are also wasting a proportionate amount of air with forced induction. Remember just because a turbo rams more air into the engine making it over 100% efficient, this does not mean that we are burning all of the air in the combustion chamber. We are adding more than 100% volume to the air but we still aren't burning it all. I'm not sure if I'm explaining this clearly or not.

Think of it this way, compressed air is just that, compressed. We have more air in the same space. If we aren't buring a certain amount of air normally, increasing the pressure and therefore amount of unburned air isn't going to help us any. This extra airflow is only good in the standpoint that there is alot of flow to spin a turbo. However turbos cause backpressure and backpressure hurts power. You NEVER want backpressure and it never helps you make more power anywhere. This includes the low end. Having too much exhaust flow area and low velocity are what causes poor low end, not lack of backpressure.

This isn't set in stone but it is a good rule of thumb. For every 1 psi of exhaust backpressure you have, it takes 2 psi more of positive pressure to offset it. If we get 3 psi of backpressure through our turbo, it will take about 6 extra psi to break even. Boost does not equal power. Volume does. If we have extra backpressure in the exhaust, some of the gasses stay in the engine and get carried over to the next cycle. This how dilutes the incoming mixture which heats it, and leaves less room for oxygen. It then takes more boost to offset these effects.

A supercharger robs power off of the crank. Everyone acts like this is terrible. What's worse is people losing power to the exhaust when they think they aren't. Meanwhile the supercharged engine can have a nice free flowing exhaust which doesn't need extra boost to overcome. Suddenly we are faced with which system uses the most power to make the most. This is debatable depending on what units are being compared but the point is made.

I got more technical than I intended to.

As to the remark about how a shorter stroke would be mroe efficient, remember that the flame front doesn't have to travel very far. My comparison was just that, a comparison. It can't actually work that way. The rotary has a long distance for the flame front to travel. The faster the engine spins, the less time the flame has to go this distance. This is why the rotary is inefficent. It can't effectively burn all of the air fast enough. It doesn't matter if the air is compressed or not. It can't usably get it all.

Thanks for the explanation! But regarding the quoted passage above, can't you just add more flame fronts to obtain a more complete burn. I'm sure it's very complicated, but instead of two plugs per combustion chamber (not sure what to call the ignition area), couldn't you add a third or even a fourth plug?

yup, mazda's done 3 spark plugs in some of theri high rpm race motors like the R26B.

another thing that can work is while increasing lead plug advance, you widen the trailing delay so there is a broader gap between the two flame fronts and you can end yoruself up with a super-trailing type of combustion.

On early prototype side Renesis engines, Mazda had tried 4 plugs per chamber. Basically there were 2 leading and 2 trailing next to each other rather than a late trailing like the R26B had. They found no improvement with them. The R26B late trailing plug did not make hardly any more power. At least not an appreciable, feelable amount. It did improve fuel economy though. This is very important in a long endurance race where you are only alloted so much fuel.

So would it be prudent for an aftermarket company to make these? Or is there room in the car to put extra spark plugs in? In theory, would I be able to go buy extra spark plugs, install them and expect better gas mileage? Seems a little farfetched as I don't think anyone has done. But it would be sweet if it were possilbe.

FWLIMABW, from my investigations of airflow, "ram air" & popular concepts of what it does, if anything, for a normal car and driving, is wildly over hyped and generally misunderstood. Maybe a more descriptive term for what I think RotaryGod wants to discuss might be "inertial ramming" (aka "velocity head" or "velocity pressure.")

Don't get me wrong, a well designed intake system is a very good thing. But, IMO its the avoidance of (a) parasitic flow losses caused by sharp edges and sudden turns, and (b) siting a good "cold air" intake point, not "ramming" air that's of greater importance in designing a good intake system for the normal car.

From what I understand of engineer-speak, air, at any speeds below say 120mph, air is relatively in- (or is that "un)-compressilbe ~ i.e. you HAVE to be running at speeds approaching 180mph, or better (its interesting that RotaryGod happens to pick this number in his hypothetical speculating) with an appropriate (i.e. well) designed intake to hope for say, at sealevel, a power increase of maybe 3%. Since the effect of velocity on the compressability of air isn't linear, i.e. the benefits of "ram air charging" fall off very rapidly as you drop from say that 180mph velocity. At anything less than 100mph, I believe the effect is basically unmeasureable. No real world street driven vehicle, and really not all that many race cars other than F1 and the Nascar guys, can practically tap the "magic" 180mph mark. A good description of the issue, and some basic illustrations of intake dos & don'ts can be found in Forbes Alrd's "Automotive Math Handbook" MBI Publishing. I think David Vizard also has some stuff on this in one or more of his various publications on proting cylinder heas.

HTH

I agree with that entriely. "Ram air" as widely used in the aftermarket is just a marketing term. That is my whole point about people saying they have "ram air" and then expecting usable gains from it. Maybe up top if their car can get moving fast enough but not in real world driving conditions. Air pressure rises as a function of the pressure squared per double in speed. I probably worded that wrong. In order to get to a point where this pressure starts to help, you need to be going pretty damn fast. It gets into the same theory as to why ramjets only work at high supersonic velocities.

I don't agree that Ram Air Intakes are worthless.

Here are some good articles about ram air intakes and Bernoulli's Equation. I read them a while ago. Following these articles, I've created some custom ram air intakes, and I feel that I've had some success. I used to own an MX-3 GS, installed a true ram air intake (one that pulled unobstructed air from the front of the car into a sealed intake) and had good results at highway speed (60-80mph).

This one is for a ram air intake for Corvettes. Though it is trying to sell an intake, I think it has some good information.

http://vararam.com/reality_of_ram_air01.html

This is a good explaination of the Bernoulli effect, and how lower pressure in a moving liquid is not necessarilly a bad thing.

http://vararam.com/reality_of_ram_air01.html

I give this link because of this quote

"Let's say we used a 6" diameter pipe that faced forwards into the airstream. We can't just taper this down into a 3" pipe since the added air will just reverse itself. We'd actually get less air into the engine this way since we'd have to speed the air up as it enters the pipe. when we speed the air up, we lower it's pressure. That is not the goal. Less pressure is less air. "

Remember that this is not always the case. If you take a 6" inlet and taper it to 3" you will be moving most if not all of the air (depending on the taper) into the intake. It will be at a lower pressure, but you will me moving 4x the air (6 in.= 28.26 sq. in./3 in. = 7.065 sq. in.).

This is some pretty complicated stuff and I have no formal schooling in this, but I'll try anyway.

CFM @ 65 MPH 3" inlet
65mph/60min = 1.0833mpm*5280 = 5,720fpm
1.5*1.5*3.14 = 7.065 sq. in./144 = .0490625 sq. ft.
5,720fpm*.0490625 sq. ft. = 280.6375CFM

CFM @ 65mph 6" inlet
3*3*3.14 = 28.26 sq. in./144 = .19625 sq. ft.
(From above) 5720fpm*.19625 = 1,122.55CFM

Now this is not taking into pressure, increased air speed through the taper, air density, and many other things I'm sure. Also, it would be before the filter and intake runners.

Giving the engine the ability to pull air as it needs without having to expend hp to pull it should increase the HP. It would be like putting in a wide open exhaust. The engine doesn't have to work as hard to move the air because there is a ready supply of it waiting.

Tell me if I'm wrong or if my math is faulty, but I still believe in true ram air and it's ability to free up hp in an engine.

Sorry for the long post.

Thanks,
Cel

Sorry, this should be the second link.

http://vararam.com/sub/tech_ref_article01.html

Ram air isn't totally worthless. It just isn't beneficial at typical everyday vehicle speeds. It is more advantageous the faster you go.

Tapering a 6" diameter pipe down to a 3" pipe can work as you've said but how you do it is very important. If you just taper it down from 6" to 3", you aren't going to get the gain in power that you think you will. A high pressure zone will develop right at the inlet. This will not cause high pressure air to enter into the engine but instead cause more air to bypass the inlet entirely and go around. What air does go into the engine will be at lower pressure as a result. If you were going fast enough this also would start to get affected but it would be much faster than the car can travel.

The 6" pipe into an airbox give the chance for air to slow down as the area increases. As it slows it rises in pressure. A high pressure in the box is a low pressure at the intake opening and more air gets drawn in. The engine feeds off of the high pressure air inside the box. Just the simple addition of a box allows the locations of the high and low pressure zones to switch. What was once a hinderance is now a benefit.

You're on the right track, but you are thinking in terms of high-speed driving. What is the speed of air at 0 mph? Ram air is not going to have any effect whatsoever. Also, when you take pressure and temperature in account, you'll wind up with mass flow rate. Anyway, that's not important. What is important is ram-air is not ideal for all situations. Perhaps aftermarket ram-air systems will result in a lower average power gain compared to our stock airbox. I believe when choosing the right intake system, select the one that best resembles the stock airbox.

Here's a mathematical representation of Bernoulli's Law. I love conservation of stuff.

http://scienceworld.wolfram.com/phys...oullisLaw.html

Shelleys, you love math way too much, it's sickening :p
Anyway, about my question on the 3rd page, can someone answer it? Or was it just a stupid question?