when running a turbo (twin) setup, is it always necessary to run high test gas, like 92+ octane, even if the CR is dropped to compensate, say around 7.5-8:1?

 

with low boost and low compression, no its not necessary but...do you really want to chance your engine to save $0.20 a gallon?

 

You can run a lot of boost with 7.5:1 and 87 octane. It’s no worse then your tuning, 92 octane isn’t any better then your tuning, both will blow the engine up if you do the wrong thing, the only difference is what point becomes “doing the wrong thing”