> Date: Thu, 30 Mar 2006 23:35:36 -0600 > From: "Scott White" <[EMAIL PROTECTED]> > Subject: Compression Ratio > > Asking for the help of number crunchers out there. > > 350, bored .030. Aftermarket pistons w/22cc dish. > Aftermarket head gaskets (.040?), 7a heads w/64 > or 67cc combustion chamber. I'm not sure of the > deck height. > > Can someone out there give me a clue where I'll be at? > > Thanks! > > Scott White
Well, it's not actually the deck height that you need to know; it's the piston-to-deck clearance. Most all aftermarket cast pistons are .015"-.030" short on compression height, so that increases the piston-to-deck clearance. If you have a factory block with an unmilled deck surface it could be .015"-.030" too tall, then add .015"-.030" for the too-short pistons and .040" for aftermarket composition head gaskets and you end up not only with way less compression than you anticipated but your quench goes out the window. You can use one of those compression ratio calculators, but be sure to use both the minimum and maximum values to see what the spread of possible compression ratios may be. FYI, factory spec for compression height on SBO pistons is 1.615". TRW forged pistons have the near correct CH of 1.612", but EVERY aftermarket cast piston out there is shorter than that. Kenneth 1971 Cutlass Supreme convertible Phoenix, AZ
