10:1 compression.... 87 octane???

[1 FMF]

compression ratio doesn't mean much anymore, you have to look at the camshaft profile and valve timing.
how long the intake valve stays open as the piston comes upward on the compression stroke will have the most affect on cylinder pressure, and cylinder pressure is what determines octane requirement. You also have to factor in volumetric efficiency (valve overlap) which changes with rpm. Ignition timing gets misunderstood when talking about octane requirements. It's just a method of controlling detonation under certain operating conditions- by retarding ignition timing you lessen cylinder pressure. You want the maximum advance in timing in order to build the greatest cylinder pressure which then yields power and combustion efficiency. Whether the engine maker designs their ignition system based on 87 or 93 octane is

But i'm sure all ignition systems today have knock retard built in so if you have lower octane gasoline that would cause pinging under maximum ignition timing, the computer would sense it, back off timing, and the engine runs fine without pinging. The way to know is get a laptop or handheld scanner capable of pulling KR numbers from the computer. I'd bet everyone here running 87 octane probably has a few degrees of KR. The norm for the LS1 drivers who run 91/93 octane is a couple degrees KR. It also largely depends on outside air temps and engine temps too.

 

[punisher]

I found this last night while looking for info on octane and compression ratios. It is a good read.

http://www.streetrodstuff.com/Articles/Engine/Detonation/

 

[wileyE]

In general the smaller the bore the higher the compression can be, a centralized spark plug hemi style combustion chamber can also tolerate more compression than an old wedge design. Newer motors run with smaller squish clearance so have less end gasses to detonate before the flame front reaches them. Knock sensors can catch detonation before it runs away. In other words lots of reasons, Since most of us were teethed on old V8's and read too many hot rod magazines we tend to define some of these values in old timer terms. Autotdarken Rotax motor is perfect example of small bore good combustion chamber design, 11.8:1 on regular, not having to pull a heavy vehicle also helps in this case.

 

[Max_Wander]

good quench pads don't hurt either. Also low r/s ratios can tolerate low octane per compression point.