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Old 11-21-2009, 11:10 PM
quadrajunk a name earned
 
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Piston Deck Height Pontiac 400?

I have a 1975 Pontiac 400. Does any one know the piston deck height for this engine? The engine is not taken apart so I can't measure it. I need the value for a CR calculator.

Thanks,
BT

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Old 11-22-2009, 12:08 PM
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You mean the pistons compression height or distance from the pin to the top of the piston? if so it`s 1.720. This won`t help calculate compression figures unless you know what type of top the piston has. If your referring to how far down is the piston from the top of the bore then the only way to know is yank the heads and check the number 1,2,7 and 8 cylinders with the piston at top dead center. This will tell you how much the deck is tipped.
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Old 11-22-2009, 01:53 PM
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Rule of thumb for total deck, center of main journal to deck surface, is 10.23", but that needs to be measured. If the deck has been squared or milled, it will be less.
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Old 11-22-2009, 04:24 PM
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Quote:
Originally Posted by DoubleVision
You mean the pistons compression height or distance from the pin to the top of the piston? if so it`s 1.720. This won`t help calculate compression figures unless you know what type of top the piston has. If your referring to how far down is the piston from the top of the bore then the only way to know is yank the heads and check the number 1,2,7 and 8 cylinders with the piston at top dead center. This will tell you how much the deck is tipped.
I am looking for how far the piston top at TCD is from the top of the block. The engine has stock flat top pistons. In a few weeks I will yank the heads and measure.

BT
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Old 11-22-2009, 07:41 PM
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Due to the tolerances of the rod lengths, piston compression heights, stroke, and block deck height, the only way you can tell is to measure.

The rod length is 6.625
The stroke is 3.75 (divided by 2 = 1.875)
Speedpro (sorry, that is all I could find in a short period of time) have a compression height of 1.714.


So, using WDCreech's deck height of 10.23 ->

10.23 - 6.625 - 1.875 - 1.714 = 0.016"

But, if you have a couple thousandths tolerance per part, that number could be 0.008" to 0.024". That is why you measure and why some suggest you measure multiple holes.
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Old 11-26-2009, 03:11 AM
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my 75 400 was zero decked and 30 off the 6x8's heads with flat tops. its right at 9to1.

http://www.youtube.com/user/LESTERDO.../2/xiylYUrwVEU

http://www.youtube.com/user/LESTERDO.../3/2JLqSztPEN4
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