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Re: Compression Ratio

From: Hank Dozier
Remote Name:
Date: January 09, 2003
Time: 12:34:05


Several ways of getting there. Start by taking the stock compression ration you have now (I guess obtainable through a Chilton's or a Model Year Service book). Using that number, cc your heads and measure your hed gasket thickness, and if there is any "negative" compression height in this engine, set the piston at TDC and cc that volume as well. Taking that number and the swept volume, do the rationality check to see how close you are to the published specs. Now you should be able to figure your oversize cleanup overbore into this swep volume equation, and see how much you gain there. If you use a thinner head gasket, this reduces the "head+gasket+piston clearance/valve relief" volume, and will tell you how much more you can get this way. For your final volume adjustment, you can either get pistons to take up the extra static volume via compression height (within valvetrain clearance limits), or with same restriction, a milling of the block deck and/or head surfaces for adjustment and truing of both. If the compression is really low (eg: 8.5:1), then obviously new pistons might do it all, and maybe are offered by someone in a 9.5:1 ratio. My personal favorite is to punch it anyway to the 59 Dodge "326" displacement (3.95" bore), since this is easily acheiveable with that block.


Last changed: July 19, 2018