Mild 383 build

It's best to calculate compression on a regular calculator as opposed to an online comp calculator which just gives you a general idea and the guy at Jegs is way off IMO. In this case lets assume there is a zero deck height and you're using a Fel Pro 8519 PT-1 which we'll round off to 10 CCs from 10.187 CCs for this demo. Lets call the aluminum head 80 CCs. Here is the math, 4.32 divided by 2 = 2.16 then 2.16 x 2.16 =4.6656, 4.6656 x 3.14 = 14.649984, 14.649984 x 3.375 = 49.443696 which is the cylinder cubic inch, 49.443696 x 16.3872 = 810.24373 which is the cylinder volume in CCs or what is now commonly called swept volume. You have no deck CCs as there is zero deck height so you add gasket plus head which is 90 CCs and add it to the cylinder volume which is 810.24373 CCs, this gives you 900.24373 CCs when the piston is at the bottom, remove that swept volume and you have 90 CCs left. 900.24373 divided by 90 and you have 10.002708, that is your compression ratio with these specs and probably not far from what Shorty will have.