Compression = Power

Dear Ralph:
Here’s the deal – I’m wondering if since my sled claims to be “87-octane” safe that I could safely increase the compression and run say 89, 91 or even higher octane fuel and make more power. Sound logic, right?
Max Harpell

This is a fairly safe generalization. Most of the engines, in stock form, that proclaim to be 87-octane safe respond nicely to a set of tighter heads with more compression, producing more power and increasing your fun-factor.

This is even more attractive if you’re running the machine at elevation. As operating elevation increases, you can generally run either a: lower octane fuel or b: more compression. An engine designed for sea-level operation but used exclusively at higher elevations can run more compression on the same octane fuel.

A few words of caution – increasing the compression ratio will tend to reduce the operating RPM, and thus the clutching will need to be adjusted to compensate. Of course, more compression for a given elevation will require higher octane fuel to prevent detonation. And, simply cutting twenty-thousandths off the head isn’t always going to work, you should be using well-designed heads from reputable shops that have taken into consideration the entire head design. Too much compression can also make the engine surge, so make such choices wisely and on the advice of seasoned tuners.