crochunter

What would be the highest safe compression to run with alloy heads using premium unleaded. Not optimax or bp ultimate. PREMIUM UNLEADED. I think it is 95 rating.

xbgs351

It depends on the camshaft, the deck height (ie quench), induction and exhaust.

crochunter

I reckon 10.8 should be ok with premiun unleaded.

Nod

As quoted above you need to know these things as its the Dynamic Compression Ratio you need to worry about. A 10.5:1 static CR engine could have a DCR of 7:1 with a BIG cam or 9.5:1 with a stock cam.
I've gotten away with 8.5:1 DCR on an iron headed V8 with .039 quench on 95 Octane and you can usually do better with Alloy heads.

aussiemart

CHI heads and 11.5 aye ok:-)))))))))

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turbomania

take notice of nod's comments just because somebody runs 11.5 comp with say chi alloy heads does not mean it wont ping with say a different cam etc , camshaft plays a big picture in it amongst lots of other things . a 9.1 static comp motor can have more dynamic comp than a 12.1 static comp motor . there are formulas for working it out . the dynamic compression has to be known not just the static compression .

Racer

Like a couple of people have said, its not the static compressio ration that matters, but the combination of parts.

Also just because the car doesn't detonate driving down to the shops, doesnt mean it wont at WOT flat out