selp

iTrader: (6)

I can get my hands on a 9.5:1. But I want to not look back and regret the idea of not going higher SCR. I will obviously use the lower octane (91 octane) in the very limited aspect, since its just for daily driving. And the E85 for the full boost.

Should I look at 10:1 instead of 10.5:1 to avoid future problems on 91 octane?
This car is driven daily to work, I take it on trips and I would like to keep the reliability and performance as well as durability.

masonh

iTrader: (8)

that sounds like a good compromise to what everyone said in this thread.

i don't think a 1/2 compression point will make of a difference either way,and i do not think the slightly higher compression(9:1 to 9.5:1) will result in slower spool.at least not any that you would notice.if anyone has proof i would like to see it.

if you are not trying to make power on pump gas then yes you could go to 10.5:1 and just make power on E85 while keeping the pump tune to low boost.

the motor i am having built is 10:1 and i plan on only running pump gas once every month or two,just to clear out the E85 gunk.with easy access to E85,that would be the only reason i see to even run pump gas at all.if i didn't have to clean my system out occasionally i would only get one tune and it would be E85.

Ted B

iTrader: (6)

Don't be wowed or puzzled by compression ratio figures. They represent one static variable in a dynamic picture that involves numerous other variables.

A higher SCR reduces the detonation threshold in the region that is most detonation prone, which here is midrange rpm. The effect is exacerbated by shorter duration cams, which raise midrange mechanical cylinder pressures.

Increasing the SCR by one full point (e.g. 9:1 to 10:1) is good for a 4-5% improvement in brake torque at MBT, which is basically the point of optimum ignition advance. It's a relatively small difference. Conversely, if fuel octane limitations prevent a higher SCR setup from reaching MBT, it will make less torque than before, despite the higher SCR. And, we all know that hp is a function of torque and rpm.

In short, what SCR is best depends heavily on the engine, fuel, cams, turbo, and of course, usage. And oh yeah, 1.5L F1 engines in the 1980s made over 1100bhp with 8.5:1 SCRs.

High_PSI

iTrader: (50)

The larger the turbo the more efficient. So a 42R at 25PSI would be far less likely to detonate then say a STOCK turbo at 25PSI.