JonDick

I've read things like "It's pointless to use high octane gas running N/A" or "You don't need high octane gas on a N/A motor" but with a high compression build, that certainly can't be the case. I haven't finished a build yet, but I'm trying to cover all of the bases. Would it happen to be as simple as doing a compression test and matching compression numbers with octane numbers?

The_Head

It depends on your static and dynamic (timing) compression. What is your compression ratio (static) going to be on your build?

An old rule of thumb used to be multiply your compression ratio by 10, but I believe that is for older motors like the pre LT1 SBC's.

chikin pickle

The higher compression you use, the more prone your engine is to compression induced detonation (knock). As a rule, generally higher compression motors need higher octane. But, it does depend on timing and tune. If you retard your timing, you can run lower octane fuel however you only can do this to a certain point before you lose power (most engines ignite the fuel/air charge before the piston reached TDC) this results in negative work being done (the engine has to work to compress the burning fuel/air charge before it can begin the power stroke).

A compression test, merely tells you the condition of your cylinder seals and rings, and as nothing to do with engine compression. Generally, you should tune high compression engines with the highest octane pump gas you can get.

Tune it with 91 and see where you can go from there.