c00lduke

I have an idea in my head why but was just wondering what te real answer was.

Thanks
~Luke

rynberg

Lower compression = you can run higher levels of boost before detonation. One of the downsides is that the motor is even weaker off of boost.

diabolical1

iTrader: (3)

yes, it's an old way of fighting detonation.

Fatman0203

What they said. Thats why real high compression N/A cars from factory usually can not take forced induction or very minimal amount.

(Look at the S2000)

c00lduke

So it would be better for high end power to have lower compression and higher boost?

diabolical1

iTrader: (3)

theoretically ... yes. but the compression isn't the only factor to consider. look at the "accepted" power potential of the S4 13B-T's vs. the 13B-REW's. if it were just a compression issue, then the S4's would have a greater power potential.

diabolical1

iTrader: (3)

double post

Kevin T. Wyum

There are two issues, chamber pressure and volume. Volume is the physical space available inside of the combustion chamber with the rotor in it's maximum position just as the valve, or port in our case, closes or is passed by as the rotor sweeps past. Lower compression has more volume or space in the chamber which is the key benefit. In a turbo application you are cramming more air in, per unit volume since the air is pressurized, with that being the case your lower compression chamber (read more space inside) will have more CID's of pressurized air inside the chamber when the port closes. This means you'll amplify the benefit of the turbocharger, you have more space filled with compressed air. So the benefit, in short, is that you're able to have more air in the combustion chamber. Sorry running out of time to explain chamber pressure, I'll leave it at there are limits, yes detonation is a side effect of excess chamber pressure due to heat etc. Bleh have to run sorry.

Kevin T. Wyum

Fatman0203

Umm nothing to do with compression. Try boost, UIM, IC, ports, timing etc etc is why the REW have more power potention. Look at the people putting the REW UIM on their T2s. Its not just for looks.

diabolical1

iTrader: (3)

which is exactly why i said ...

BLUE TII

iTrader: (9)

Basically, your turbo is a MUCH more efficient means of compressing your intake charge than your rotor. Especially since it has the benifit of the intercooler.

Since the turbo is more efficient compressor it creates less combustion chamber heat before ignition to run higher boost and lower compression than same boost and higher compression. This means there is less chance of detonation- or you can run more boost w/ same chance of detonation.

The off boost is not as good, but I believe in a well matched system there really is no off boost- I run low comp rotors and data logs show I get boost from 2,500rpm in 1st faster than I can push the pedal.


Another benifit of the low comp rotors is that they are stronger due to more material on rotor face- though this means more weight. Also the rotor depression is deeper so there should be better combustion between leading and trailing area of combustion chamber.

Also, I believe the higher safe street boost afforded by low comp rotors puts you right in the best efficiency range of the large truck turbos we commonly use.

The guys that really need the high comp rotors AND high boost are the ones running on alchohol where they reach the limits of the turbo compressor effieciency (30-40psi boost) and so can add engine compression safely since the octane and charge cooling properties of alchy are so good.

Otherwise, high comp rotors are just a concession to driveability on a turbo car that must have high backpressure exhaust (emmisions).

carx7

iTrader: (31)

Just curious, have you ever actually seen a dyno comparison between the FD and FC UIM? Cause I've been looking forever. I have never seen anything that actually proves they make more power and as far as I know it very well may be "just for looks" I would love to be proven wrong though.

pinkfloyd

Has it been proven that they make more power...no. Is it true that the runners are bigger yes. Is it true that it flows better, from what i know yes it flows a little better and it is bigger. So in the end is it better. we will never know.

Fatman0203

Dyno I dont think anyone has. Yet probably in low boost operation (12 and under) probably not much difference and may effect efficiency partly. Yet I know for a fact that once boost goes over 12 around 15 and up the runner length, and other factors of the 3rdgen UIM is better.