Tony the Tiger

Too low of a compression then you will lose efficiency as well.. As compression drops, BSFC increases, so soon you'll realize that the same turbo you have can no longer support the amazing peak HP numbers that you regularly see with common setups in the mid 9.5:1 CR. With lower CR, it takes more fuel to make the same HP, not just more boost.

The same turbo putting out the same CFM into the engine, the lower compression engine will make lesser power with the same amount of air. 50lbs/min of airflow is no longer 500+ WHP if you drop the compression too low on a Honda. It starts to become like a DSM, or other low compression motors when it needs a bigger turbo to make the same HP as a typical boosted Honda which CR's are always within the 9 range. There will be more unburnt gases and higher EGT's with low CR, so your turbine sizing has to change. In exchange though, more EGT's and unburnt gases will yield faster turbine response within spool RPM range, but the need to upsize the turbine housing will cause a loss of low-end spool.

The key is to find a perfect combination.

My Integra on the other hand, I have recently dropped my compression ratio down to 7.8:1 CR since last year...ROFL Currentiy it is pumping out 660-670 WHP on 94 oct, and this setup was to feed my curiousity of ultra low CR setups. Only drop the compression if you are limited by octane.

TheShodan

iTrader: (14)

That's on the tuner and his/her ability to get timing and fuel in the right spots. On turbos you CAN'T take CFM flow out of the equation. that's the entire point. using a specific turbocharger that can get to effective compression more efficiently. Its not just about POWER, its about off-boost accelration. I'll take a 10.0:1 with the right efficiency on the engine and out accelerate the same car with a lower static compression.

If you don't have a competent tuner, sure, keep the static compression low. But, with the right facilities, personnel, and equipment, there is no reason why 10.0:1 can't be done without good reliability

96 GSR-T

amazing reply as always, your stating lower compression spool the turbo faster? then what does a higher comp ratio do slow down spool?

tony413

lol tony just told you why the lower CR spooled faster, it has more unburnt gas and higher EGT's.

think about when you tune a higher CR car whether it be N/A or turbo, the IDEA tune will use up ALL air and fuel in the combustion event because its operating at full efficiency. also with a "perfect" tune its rumored that you should be able to pull the head an not see carbon build or deposits, but remember thats "perfect."

F.I.Motorsports

Its possible not just rumored, About 5 yrs ago I had my car tuned and put about 15,000 miles and when I tore it apart to build it (it was a stock rebuilt motor) looked like it did when I first assembled it.

but if you already have the motor built and the turbo set-up then I would just put it together and see what you can make, if your still not satisfied then you can upgrade the turbo later and retune.

tony413

i've seen some good set-up but they all had carbon somewhere.

t00JDM

thanks for the help guys....tons of good info and some homework for me to do....for the time being im only looking to get mid 400s and as soon as i get a daily beater ill up the boost along with turbo

t00JDM

is this so or just myth cuz its not on the car yet but i do have it and was pretty anxious to put it in.

tony413

no its not a myth, just get an ATI damper