Compression ratio calculation

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May 14, 2003 | 06:23 PM

SgtSkip

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Joined: Sep 1999

Posts: 436

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From: Beaufort, SC

Compression ratio calculation

Looks like I'm geting world 67cc heads for my 350. How do I figure my compression ratio? I'll probably be getting flat top pistons as well.

May 14, 2003 | 06:31 PM

Auggie

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Joined: Jul 1999

Posts: 811

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From: Maple Grove MN USA

Car: 1984 Z28 Camaro

Engine: H.O. 355 NOS

Transmission: 700R4

Well, I think its right around 9.79 to 1?

Auggie

May 14, 2003 | 08:27 PM

F-BIRD'88

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Joined: Sep 2001

Posts: 6,111

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From: Ontario, Canada

Car: 1988 Firebird S/E

Engine: 406Ci Vortec SBC

Transmission: TH-350/3500stall

Axle/Gears: 7.5" Auburn 4.10 Posi-Traction

You can calculate it here:

Compression Ratio Calc

You'll need to know the piston deck clearance spec.
The valve relief volume is about 5cc's on a flat top piston.

Some replacement flat top pistons are .025" from the top
other common ones are .045" (on a standard block) This will affect the final compression ratio. If the block has been "decked" this will affect it to.

You can select different thickness head gaskets to adjust the compression too. .015" .028" .039" .051" are available.