JSR_AP2

What is the highest CR to safely run daily on 91 octane? I've seen 12.7:1 on 93, but have not found much info on 91.

Thanks.

s2000Junky

The stock 11:1

Fierc3

my cbr is 12.3 : 1 but thats 250cc per cyl. vs 500cc per cyl

JSR_AP2

I recall guys running mid to high 11 (up to 11.7:1) on B-series motors on 91 octane. I know the difference chamber shapes can affect what is "safe", but seeing as 93 octane can run 12.7CR, is 2 octane points lower really force sub-12:1 compression ratios on 91?

No Cali people running high compression NA motors?

s2000Junky

We know what the Honda Engineers think. Why dont you call up a few tuning shops and ask the Engine builders there what they think is safe?

The JDM F20 is 11.5:1 is it not? And what fuel do they run?

nipponS2000

The JDM motor is 11.7.

s2000Junky

Whats the highest OCT fuel they have readily available to run for consumers at the pump?

nipponS2000

I think there are some differences between the US,Europe and Asia in fuels.Here in Greece we got 95ron,98ron and 100+ron gas available at the pump.For the first ap1 models with 11.1 cr and 9100rev limiter the minimum ron was 98.For the later models(f20c2 engine,in europe we don't have the f22 motor) with 11.1 cr again but with 8800rev limiter the minimum ron was 95.So i guess for the jdm motor the 100+ron is the minimum.But i don't know if there are any differnces in counting the rons between US and Europe.Maybe the us 91ron is the same with europe's 95 ron and the us 93ron is the same with europe's 98ron.Otherwise the cr wouldn't be the same at both US and Europe if there was a significant difference in fuels.

JSR_AP2

I believe Japan uses 96 RON as their "high octane" which is between 91 and 92 octane (US rating).

I've only spoken to 2 shops and the max they recommended was 12:1 on 91, though I didn't get that feeling that they had much experience with high compression on 91 octane F20/F22 builds.

I was hoping I'd gather more user experiences, but it seems this may be a limited chartered area.

s2000Junky

I always try to air on the side of caution, you want a safe and reliable motor, yet you want it to perform as best as possible. It’s sort of too bad if you’re going through the expense to build a motor, only to be able to run it on 91.