our crazy rapist government policy says 97/98 octane fuel is BAD and thay slap an extra 30% tax on it so says my local fuel retailer
my engine is type F20C2, quoting 98 as the desired octane, with a permission to use 95 provided it doesn't cause knocking.
what performance decrease should I expect if I use the lower octane rating?

 

Before too much misunderstanding spreads, keep in mind that the US method of measuring Octane is not the same as the Euro or Japanese method of measuring Octane. The US method results in a number that is about 3% lower. Hence the euro 97 or 98 octane number is about a 94-95 in the US.

That being said, I am not familiar with the engine designations but if your engine is the JDM spec 11.7:1 compression ratio, then you probably do need the higher octane. The S2000 engine has a knock sensor that will adjust the ignition timing to accomodate lower octane fuel with a performance loss. Based on the published numbers for the different octane #'s on my Odyssey, I would suspect that going with 3-4 octane numbers lower is likely to lose you about 3-4% in hp and torque.

[Edited by s2ktaxi on 03-28-2001 at 01:06 PM]