92-93 pistons - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-08-2005, 08:24 PM   #11
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The answer is right infront of ya

88-92
Head recess: .250" deep

93-95
Head recess: .295" deep

This means to me that there'* a difference in the combustion chamber between the years but I haven't been able to measure. I'll getcha more info as soon as I can.
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Old 04-08-2005, 10:54 PM   #12
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I'm not so sure I want to change my compression ratio. Can I get slightly thinner head gaskets?
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Old 04-09-2005, 01:37 AM   #13
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"And top ring height DOES have a small effect on compression ratio. I know I'm not mistaken on that."

I'm afraid you are.

Care to explain why you think so?
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Old 04-09-2005, 01:45 AM   #14
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Because there is volume in there, crevice volume. In my engine design engineering class, we calculated compression ratio using stroke, crevice volume, clearence height, and combustion chamber volume, as well as any other variables needed to get volume. That crevice volume also contributes to unburnt fuel.
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Old 04-09-2005, 01:49 AM   #15
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Before you jump all over that, there is the right way, and there is the way it'* done because it doesn't change it a whole lot. I just wanna keep it just how it is to avoid problems.
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Old 04-09-2005, 01:56 AM   #16
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"Because there is volume in there, crevice volume. In my engine design engineering class, we calculated compression ratio using stroke, crevice volume, clearence height, and combustion chamber volume, as well as any other variables needed to get volume. That crevice volume also contributes to unburnt fuel."

"Crevice volume" is not a component of compression ratio calculation. If you're describing notches in a piston, for instance, that'* a component. The "crevice" you describe is part of the cylinder volume and is not affected by ring height.

I think you're confusing "ring heighth: with "deck heighth." Deck heighth does make a difference.

Here'* a link that explains the process.

http://www.hotrod.com/techarticles/54258/
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Old 04-09-2005, 05:10 AM   #17
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If anything you'd drop the compression slightly from what I read and your ideas. More boost friendly (and dependant) but this is such a small scale...

Deck the 93 heads if you don't like the extra room IMO...
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Old 04-09-2005, 11:41 AM   #18
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Ok, we were taught different. I dug out my book, and I accuratly remember what I was taught. For the sake of sanity, I won't quote it. I'm most concerned about the overall effect of swapping the heads from 93 to 92.


DrJay, if you know, what is it about the pistons that will change compression ratio? Any new measurements of the heads?
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Old 04-09-2005, 12:29 PM   #19
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I think he may be moving from West to Southeast right now.
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