[MBS]

Originally Posted by two_wheel_mayhem

The reason the engine is designed to run 87 octane with 11.3:1 is because it is a direct injected engine, which changes things. You guys always want to argue with the engineers that design things, thinking you know better. It could handle 13.5:1 easily if GM engineers intended for it to be run on 93 octane fuel, which would probably move it's peak power up to around 350 horsepower. They could also let it turn a few more thousand RPM's with great benefit, but that's another story and is political....warranties. Anyway, the 3.6 runs at maximum performance with the designed fuel. The engineers did not crutch the timing tables just so they could say it runs on 87 octane, that would cause poor economy and emissions.

There's more to it than "this compression ratio requires this octane fuel." That only works when you are talking about a typical pushrod V8 engine with flat top pistons and wedge shaped chambers. Other factors include cylinder head/piston design and material used, bore size, altitude, engine temperature, engine tolerances (specifically piston to cylinder wall clearance), vehicle weight, and gearing.

As far as fuel additives they are all worthless no matter what vehicle you have, at best they boost your octane. If your fuel system gets gummed up no magic in a bottle will fix that. Fuel injection can sit for years and fire right back up like it was yesterday.

You had me till the last paragraph , Saying fuel additives are worthless is wrong, GM recommends only top-tier gasoline which has more additives than the other stations sell ,