As title really. Wondered the sort of backpressures people have with different setups and boost levels.
Im thinking due to the rotary design that theyd not cope so well with pre-turbine backpressure as well as piston engine cars, but dont know the sort of ballpark figures, and could be hugely wrong anyhow, so wondered if anyone had any numbers from their cars?

Thanks

 

howard coleman, rice racing(i dont think hes here anymore but can be found on aquamist forums) are the two i can think of currently.

howard coleman has a few threads on the subject.

z

 

I did a search but didnt find much, apart from some stuff by Howard 6 years ago when it was actually him asking about it.

Seems 1:1 is ideal world, as ever, but not really found how much most rotary setups run yet.

If anyone has any links that would be good.

Also really wonder what mine is running, a HKS T04E on a tubular manifold at 1bar- I cant really fit a gauge without removing it all, but if anyone else has tried similar id love to know.

 

I run my car MAP/EMAP to calculate efficiency so I log backpressure. 1:1 is attainable in a rotary, I see ~130% efficiency (that's intake higher than exhaust..) at 9psi at torque peak, drops off to 1:1 till redline.

 

What are the specs on your turbo?

 

Holset H1E with 22cm exhaust housing, probably going to step up to the 26cm. Compressor: 60/82mm, Turbine: 76/65mm

 

How much boost are you running?

Thats usually the hardest thing, keeping anywhere close to 1:1 once running any decent boost levels.

 

That's at 9psi. At 14psi I saw up to 138% efficiency but dropped off sooner, hence going to the larger 26cm housing.

 

im pretty sure this is what has caused me to pop to motors. running stock 13bre's with a precision 6776e(.60 comp, .68exh ptrim) i know the housing is two small now and from what ive read i prob had way too much pre turbine back pressure cause hot air being pushed back into the motor and heating up my intake charge causing rediculious detonation.

 

backpressure: a really important topic.

because i elected to build a twin (as in two) TO4 setup in 04 i decided i was in uncharted waters and had better fully instrument everything.

after talking w a bunch of turbo people i had suggestions all over the map as to hotside sizing. after splitting both initially suggested turbine housings (too much backpressure... two T3 .48s w stage 2 wheels) i decided it it was time to stop guessing.

i added bungs on the manifolds that allowed me to attach a stainless steel brakeline. i connected it to a 0-100 psi FJO pressure sensor and wired it to my Datalogit.

result: loggable digital back pressure or EMP (exhaust manifold pressure).

and it didn't look great. after a few shuffles w turbine wheel sizing and housings i ended up around 1.3 at 20 psi.

i was swinging two stage 5 wheels or 10.816 sq inches of average turbine area.

the turbo above w the P trim (65/74) is 5.89 sq inches. the key is that it is 92% of the compressor area. i really really like the GT35 size compressor w the P trim hotside for 400-450rotary app.

too much EMP does dilute the intake charge causing alot of things to happen all bad.

torque/hp is all about airflow and EMP is one of the key factors as to setting the limit.

hc

 

I'm hoping that Aaron can soon add some more to this thread when they tune my car. Actually, now that I think of it, it was his craftsmanship that created the central EMP plumbing component, the divided manifold collector. Thankfully, he'll have a vested interest in my car's tune!

I suspect boost levels should be similar to Howard's.

A good discussion about this was also had over the EFI101 Forum: Let's have an Exhaust Back Pressure Discussion. However, it was not rotary-specific.

 

hey howard, so do you also think my tiny exh played a role in my detenation prob and low power? i made 323 on a stock port re motor at 1 bar.

 

Total combinations of parts and tuning make power, your exhaust housing is only one piece of the puzzle. It is not helping your power but on its own doesnt explain the "low" power. what is your compression like, what apex seals, air filter, intercooler, etc. and of course the tune is very important.

Also a turbine housing cannot blow a motor. Poor tuning, part failure, or freak occurances blow motors. In a "normal" setup 323hp is low for 15psi, if the exhaust restriction is killing your power that bad it will be more apparent as the motors flow increases. Maybe your setup would make 315hp at 10psi, in that case poor tuning becomes the culprit with part selection limiting overall power.

Without knowing all the details its impossible to say why a motor went, exhaust manifold back pressure is only a small piece of the puzzle.

 

on page 7, Enzo mentioned that with 91mm compressor on 13B, he saw 38 psi turbine inlet pressure with 50 psi boost. I highly suspect it is full peripheral port engine.

Also RICE RACING over ausrotary has huge thread about dataloging of his own car.
13B Street port, T04Z 1.0 A/R divided, 18 psi boost, 17 psi pre-turbo, 4 psi post-turbo. With change in exhaust setup post turbo at 17 psi boost it was 12 psi...