Re: How much overbore?

Posted by 55PackardGuy On 2010/12/17 23:22:45

A 396 would be a great option, IMO, especially because that's the cid claimed by Chevy for the big-block Chevelle, which actually ran about 402, I believe. (But the pledge to stay under 400 inches in midsize GM cars meant some creative math was required.)

So a true 396 could be easily "stretched" to 400 for the full-size Packard. At least in my mind. If 6 inches is close enough for the mighty GM, 4 inches would be an easy fudge for a modification.

Thanks for the bore numbers, Craig, and for the possible configurations.

But Jack, seriously, the Packard would've had to be "stroked" to get to anything much over 400, correct?

Fr'instance. the Cadillac 500 had a bore and stroke of 4.30 x 4.304, vs the Packard 374 of 4 1/8 "x 3 1/2".

You'd have to have an extremely "oversquare" engine to go over 400 cid with a 3 1/2" stroke.

By the way, I think the extra revving possible with a shorter stroke/slower piston speed is a much more attractive engine design than a "stroker" approach. But that's just my personal opinion.

Is a .125 (1/8") overbore feasible with a stock 374? Or to go to the same 4 1/4" bore on a 352? Everything else being equal, $800 for a set of 8 pistons is not so terrible, especially compared to the total cost of the teardown and rebuild.

Have you done any work on intake and/or exhaust ports and other head work on these? I have heard that the intake is quite adequate on these engines, but the exhaust side is limiting. I'm not talking headers or anything, just polishing and porting.