I'll be having my heads milled a little bit to compensate for the valve reliefs and I've been thinking about overall compression. What do you guys suggest I run as a final number? I've heard 9.5:1 will require a premium gas, but couldn't I kick the timing back for weekday driving?
if you check the owners manual for the older mavs, 92 octane is the lowest suggested octane for stock. you can adjust to run on the 87 junk with 9.5 to 1. just expect it to not run as good. i suggest running premium.
depends 100% on the camshaft. 9.5 on a 280 duration cam, you might get away with 87. Stock cam, better run 93.
What he said. My car pinged on 87 when it was stock. When I rebuilt it, I milled the heads and ran an e-303 cam. It liked the low test camel pee after that.
Too many variables... As a rule of thumb: 9:1 with cast heads and 10:1 with aluminum heads. That will get you by. Then you can add some timing when you run premium, or drop it back for 87. Those numbers can change though. If you polish your forged pistons, run a cooler plug, and polish the chambers on your aluminum head with high quality valves... You can get almost to 11:1. With computer aid, 93 octane, and SEFI, modern engines run up to 11.4:1. (GM LS engines) The cam can make things better or worse too, at the primary rpm range for your style of driving. A cam with more overlap can lessen problems with detonation at lower rpms. Or an RV cam can make things worse. The problem is that an RV cam doesn't help you if you want your engine to make power at a higher RPM, and a big cam doesn't make as much lower rpm grunt, while at higher rpm, your compression comes back into play as the overlap effect is lost. So cams can be a bandaid for low compression, by using an RV cam as a pressure builder, but a big cam does little to bandaid too much compression. My .02 Dave
