Re: How much overbore?

Posted by Jack Vines On 2010/12/16 12:25:43

1. The 320", 352" and 374" are each unique castings. Each can be bored 1/8" (.125") with no problems.

2. The old Hot Rod Magazine and other urban legends that Packard V8s can be bored 1/4" is not best science. I've sonic-tested many blocks and the walls are usually .250"-.300" thick. The Packard block is so tall, the walls need to be thicker than the much shorter SBC.

3. I bore 352"s to 374" and use carefully selected used 374" pistons. Measuring many pistons has shown two out of three used 374" pistons will have collapsed skirts. I've never been able to determine why; just that it happens.

4. Yes, it is possible to bore a 374" to 4.270" to give exactly 400". However, that requires an $800 set of custom forged pistons. I once machined a set of BBC pistons to fit, but that cost about as much as the forgings.

5. I'm having a set of 4.165" forged pistons made for my supercharged engine. I'd rather have the thicker wall for less risk of overheating and better ring seal than the few extra cubic inches.

jack vines