Compression And Timing Plate

[jstew]

When do you have to start running straight race gas in regards to timing and compression. For instance, I want to run a 4 degree advance in timing and say I have a 170 psi for each cylinder. Do I need to run straight race gas? I know timing has an effect on detonation, but how much? Is there a general rule of thumb between how much timing and compression, before you need to switch over.

Thanks,

jstew

[SDD]

With the compression you listed with advanced timing (+4) you should be running about 100 octane gas just to be safe. Some people run into problems running a stock head with +4 timing on pump gas. All motors are slightly different so you might not need to but it's better safe than rebuilding a motor!