I was looking at all the different 305s in the tech data that have different compression ratios. What is different about those engines, did they change the heads, or the pistons?

 

With the choice of 305s available in ThirdGens, the compression ratio difference was acomplished with pistons. Head chamber volumes were relatively constant at 54cc.

Earlier SBC 305s had various chamber volumes and piston designs, producing a variety of static compression ratios from 8.4:1 to 9.6:1 depending on the vehicle. A 1976 305 in a Malibu or Nova may have had 8.5:1 compression from the dished pistons and 72cc heads, producing a lame 140 HP. The '79 versions may have been as low as 8.4:1 depending on the vehicle, and the later 305s could be raised to 9.6:1 (actually 9.58:1) with flat pistons, 54cc heads, and thin head gaskets used in the HO engines like the L69.

 

BTW - You wouldn't be from around Tiffin, would you?

 

Thanks for the information. Tiffin is up north, I am about seventy miles east of columbus in a small town.