I'm about to order my rebuild kit w/ new pistons. I thought my stage 1 engine was a 71 breed but the heads appears to have a large 72 cast into the main body. I know that the pistons for this engine are low compression and the combustion chambers are larger than the 70' version. Can I ask for the 1970 version pistons to get a higher compression ratio and not screw anything else up (valve clearance, etc...) What will be the final compression with these pistons and the 72 heads and will it run ok on pump gas without issue. And finally, will the package rebuild kit in federal mogul brand for a 70 model engine be a direct fit with 72 block and heads. I think it won't be a problem but I like to hear from the more well traveled folks. Thanks a lot for the help.
You can do what you are thinking, the trouble may be finding the 70 high compression pistons. Most parts stores donot list them and automatically put you into the low compression ones. Your intake gasket will be different for the 72 heads than it would be for a 70 engine, so make sure you order for a 72 to 76 engine. The rest of the gaskets and parts will be the same. You will probably be in the low 9 to 1 compression range if no block surfacing is doneor head milling. Jim Burek P.A.E. ENTERPRISES www.paeenterprises.com
Lower Compression Pistons Thanks Jim, Do the lower compression pistons make a sizeable performance difference as opposed to the 70 pistons in the area of horsepower and torque for a mild street build. Rich
Hi Rich, I would say to go for the 70 pistons. The chamber cc's are the same between 70-72 so your compression would be roughly the same. With thicker headgaskets your going to be in the 9.6:1 area which is still very good for pump gas. If you go with low compression pistons I would say switch to 400-430 heads with thin metal gaskets as the chambers are smaller and this will raise your compression. You want your compression to be between 9:1 and 10.5:1 if your doing daily driving. Below 9:1 and you're just robbing hp and torque.
Re: Lower Compression Pistons Well, the factory only showed about a 15 horsepower loss between the high compression 70 455 and the lower compression 71 engine. I believe there was a larger drop in torque. I know I built a 455 many years a go with the low compression pistons, with ported heads , and a decent cam, the thing still ran strong. Jim Burek
