rotarygod

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.

T-von

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?

AbusiveWombat

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.

rotarygod

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.

T-von

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

neit_jnf

just crazy!

j/k :D

rotarygod

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!

T-von

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?

rotarygod

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.

AbusiveWombat

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.

T-von

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.

xXcfeboXx

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...

Lock & Load

I have an allmighty torque headache .OUCH :D

So much to learn in so little time .

cheers
michael

rotarygod

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

wakeech

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

thanks guys.