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Old 08-04-2010, 11:42 PM
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Compresion Qusetion BBC

I have a mid 70s Chev. 454 Flat top piston, .030 over, stock steel crank,stock rods block decked .005 heads shaved .005 cyl. head # 353049
Please tell me how much compression this motor has thanks in advance! I am trying to pick a cam

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Old 08-05-2010, 12:12 AM
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Quote:
Originally Posted by TonkaYJ
I have a mid 70s Chev. 454 Flat top piston, .030 over, stock steel crank,stock rods block decked .005 heads shaved .005 cyl. head # 353049
Please tell me how much compression this motor has thanks in advance! I am trying to pick a cam
Assuming 3 cc's in the piston, 943 cc's in the cylinder, 122 cc's in the chambers, 4.7 cc's in the piston deck height (piston down in the bore 0.020") and using a 10 cc gasket, the total ingested with the intake valve open is 1082.7 cc's. With the piston at TDC, the volume is 139.7 cc's. Dividing the larger by the smaller will yield 7.75:1 static compression ratio. This is a plow horse, not a race horse. Don't ruin it by installing a race cam. I wouldn't use over 200 degrees duration @ 0.050" tappet lift.

If you want more, either change the heads or change the pistons or change both.
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Old 08-05-2010, 01:29 AM
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Flat top piston was a big mistake, very hard to find a head that will have a small enough combustion chamber to have enough compression to be anything other than a tow motor
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Old 08-08-2010, 07:43 AM
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OK I ordered a set of 25.5cc dome pistons will that help now what should my compression be
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Old 08-08-2010, 08:32 AM
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Quote:
Originally Posted by TonkaYJ
OK I ordered a set of 25.5cc dome pistons will that help now what should my compression be
There are hundreds of online calculators you can use to figure CR with. I often use: http://www.wheelspin.net/calc/calc2.html

You have to measure the chambers of the 049 heads. They are said to be anywhere from 113cc to 122cc, and after this long, they could have been milled any number of times even if there was a reliable "stock" volume to use.

Bottom line is you will be in the area of 10:1.
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