Quote:
Originally Posted by olddog
I don't have the expertise to give you an answer, but I do know enough to tell you that you need to give more information, if you want reasonably accurate answer.
Aluminum heads or cast iron?
The combustion chamber and piston combination can give more or less swirling and quench, which can have an impact.
Cam timing can give a much lower dynamic compression than the static compression.
All these factors combine to make big differences that is over my head.
My rough rule of thumb is stay around 9.5 with iron head and 10.5 with aluminum heads for a street engines. I could be dead wrong depending on your combination.
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I'd say the above is fairly wise words from someone who doesn't believe he has the "expertise".
It's all about effective compression ratio (static CR versus cam duration, specifically inlet valve closure), also known as dynamic compression ratio.
You can have an engine of 9:1 with an economy cam (short duration) rattle its head off from detonation, and yet still have a 10.5:1 motor with a long duration cam not ping at all.
So if you're limited to 93 octane, I'd suggest building more cubes at milder engine spec settings. You'll make more reliable figures that way.