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if i put a n47 head on a f 54 block what will my compresson be.will i have a problem with running pump gas.and how much h/p will i gain.thanks ahead of time
 

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You need more info to do a accrurate compression ratio figure.The formula is (swept volume +chamber volume +piston dish + head gasket +piston chamber volume)/(Chamber volume + piston dish +head gasket + piston chamber)=compression ratio. So here's the run down(i took some liberties here since you did not include things like piston type or bore size)
N47 head 44.6cc
Head gasket 7cc(a common average if you are using a fel-pro ect)
Piston 38.1mm pin height/0cc dish 86mm bore
Swept volume=bore radius squaredx3.14xstroke or 43x43x3.14x79=459cc
Piston chamber volume is a little more complicated S/2+rod+piston pin height=Height of piston in relationship to block at TDC,this can be a + or - depending on combo but a production motor should be -.So figuring a L28 crank stroke of 79mm this would come out to 207.8 or just about even with the block height figure of 207.85 so this would be a wash with the flat top pistons .
So with this info here's how it comes out
459+44.6+0+7+0/44.6+0+7+0=10.0:1
Now this one is fairly simple and alot of Z guys could give it to you off the top of there head, but my intention was to show you how little things like the bore size or piston type can change things dramaticly,also now that you have the formulas you can do your own check for whaterver components you decide to use.
 
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