Heads milled and compression question.....
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Le Mans Master
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Heads milled and compression question.....
If my 90's heads are milled, say, .020 or .025, how much of a change in CR would that be? How would this effect driveability? Would this necessitate a decrease in spark advance to keep from pinging?
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Re: Heads milled and compression question..... (Marcho Polo)
Craig, we may have talked about this briefly but heres my take on it. .02 isnt enough to make a huge difference. You may have bumped up your CR a little bit but .025 isnt enough to worry about. Did you ever find out what the compressed thickness of the head gasket was ? That could tell you alot. Just the increase in CR alone shouldnt necessitate a decrease in spark advance. I think I figured out that my CR was somewhere in the 10.5 or 10.75 -1 range even with having the thinner head gasket, 0.029 compressed thickness.
You may try posting this over in the engine mods section. Theres alot of gearheads over there.
You may try posting this over in the engine mods section. Theres alot of gearheads over there.
Burning Brakes
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Re: Heads milled and compression question..... (Marcho Polo)
If I remember right it is up to 1 cc for .010 I think that is up to .20 compression but it is different from engine to engine.
Like if you take 0.10 of a 15:1 SBC you will get around 15.5:1 but if you take the same of a 9:1 BBC you will only get about 9.10:1
I hope Im remembering this right maybe somebody out there can help you better.
Jay
Like if you take 0.10 of a 15:1 SBC you will get around 15.5:1 but if you take the same of a 9:1 BBC you will only get about 9.10:1
I hope Im remembering this right maybe somebody out there can help you better.
Jay
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Le Mans Master
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Re: Heads milled and compression question..... (MrJay)
Yeah, not sure.... It seems I remember seeing somewhere that .025 off a 58cc combustion chamber made it around 55cc or 54cc which is a big difference to me.
Still trying to find the compressed height of the 7733PT Fel Pro's. I posted over in engine mod section too.
Still trying to find the compressed height of the 7733PT Fel Pro's. I posted over in engine mod section too.
