The title says it. Will the approximately 15% lower compression from the use of composite head gaskets be enough to allow the use of 87 octane regular or 89 octane mid-grade? Are there other reasons to use premium other than detonation? Thanks, I am looking to buy a 99 with blown head gasket and want to run lower octane.

 

bite the bullet use the high octane. I'm sure someone will argue the point, but I think you get better MPG with it.

 

The later engines come with composite head gaskets. Without knowing the demensions of each type and doing the math I don't know what the compression differance is, from what I've read here the thickness differance is maybe .020. That much differance will not reduce compression by 15%. Using Regular fuel may be OK at sea level with no hills or load in the vehicle, but it will result in retarded ignition timing, higher combustion temps, lower fuel mileage. Not worth the risk to me.

 

Yeah, I guess the 99 already had the composite gaskets and therefore would see no change. PREMIUM is about $4.00 per gallon in CA right now....YUCK!