Originally Posted by hellosailor
Folks have been taught to think "high test" will make their engines run better. Ignoring the new ones with detonation sensors, that's been fooling the masses for over 50 years.
Using low test to run a high compression engine? Sure, that's one way to do it. Or you can start with building a stronger engine. Many ways to skin that cat. The faster the "boom", the faster the pistons can move, and velocity buys more power than just increasing the mass. That's why aluminum baseball bats hit further than wood.
Two problems with that;
1. Detonation sensors work by dialing back timing advance - that really DOES steal power.
In addition to decades of hot rodding, I am also speaking from very recent experience with my wife's supercharged Jag. Obviously it requires high octane, as specified in the owners manual but it didn't specify an octane. Since 92 is the best available in the States, I figured 91 would be O/K here.
It was demonstrating some less that stellar performance - exactly like too little timing advance - it was "lazy" on hard acceleration. I tried some 94 octane that Chevron sells here and problem solved. The computer was dialing back the timing to compensate for the inadequate octane. So much for "stealing power". I expect the car would barely run on low test.
2. You can't BUILD an engine that can withstand detonation - even diesels don't actually detonate. They are fired by compression heat but the fuel is introduced so it burns, not explodes. You'd need solid pistons and engine blocks to even come close to being strong enough. Ask any race engine builder - they routinely run 14 to 1 and 15 to 1 cr's and have to use 115 octane race gas.
You have to use the octane your engine requires. Most cars require only low test and anything higher is just a waste of money but if the engine needs it you HAVE TO use higher octane gas.