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How much overbore will a Packard 352 engine take? Was the same casting used for the 374? I believe the 374 was bored out to 4 1/8"

Could you get 400 ci out of a Packard block by overboring, or would it have to be stroked?

Just wondering the feasibility of having a Packard "400" that really was a 400.

They may have changed the cores between 55 and 56 so you may not be able to bore out a 352 to a 374. I would think it was common practice to change the cores because the walls should be a certain thickness. AND you could have a core shift when pouring. The exterior blocks are the same, but that doesn't mean the internals are the same.
A competent machine shop would blueprint the block first and then they would know for sure. In the Feb 57 issue of HOTROD there was a Stude Golden Hawk that was bored out to 374, but it was also stroked, given a dual-4 intake and a magneto ignition. It was turning over 140mph at Bonneville with a bad magneto ignition. The car was from Texas, but I don't know what happened to it.

Boring either a 1955 or 1956 352 +0.125in is no problem. If you want confirmation, have the cylinder walls sonic tested for thickness.

Here's the magazine article on the 56J bored to 414CID. Lesser stroke would give exactly 400CID obviously.

1956packardpanther.com/PV8C/HRM195702A.html

Bring your wallet because you will need custom pistons and crank at least.

Craig

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

Thanks all,

Jack,

So how close can you get to 400 cid with standard pistons. I'm so dumb, I don't even know what a 374 bored 1/8" inch would yield in cid. But I'd like to know.

It would make sense that it's safest to go with the block that requires the least overbore to achieve the cid you want. So the 374 would be the safest choice. Or not?

Finally, I do know from secondhand experience that the heads on a 352 cid Packard V8 can be planed a full 1/8" as my father did so on a '55 400. So, there seems to be lots of material there for machining the heads if you desire more compression rather than more displacement.

Custom pistons and cranks are not really what I have in mind. It's more to find out what Packard could have done to increase the cid of the 374 in '57, without huge expense.

I'm dreaming of a 'tweaked' Packard 400 that would've been feasible as a '57 model.

Quote:

I've heard somewhere that the 57 prototype was 440CID. I never read bore or stroke for same. I also read somewhere that the "ultimate" CID for the Packard block was to be 500CID, but again no bore or stroke for same.

Craig

Craig,

I'd be happy with the most feasible overbore near 400 cid that would accommodate readily available pistons/rings. Nothing radical, just doable, as the manufacturer might approach it as an enticing upgrade in a new model.

It might also be generally helpful to Packard enthusiasts to have an idea what could be done to overbore V8 blocks with worn or damaged bores... without breaking the bank on custom pistons.

(BTW, nice pic of your Patrician!)

55PackardGuyQuote:

Not possible to do cheaply. 374 and any oversize pistons you can buy are it. 374+.030 is 380CID, 374+.060 is 385CID and 374+.125 is 396CID. However, I doubt that you can find off-the-shelf 374 pistons in anything other than +0.030 max.

Quote: Thanks! I can thank KevinAZ on Thanksgiving day for that one. A larger picture is here if you are interested:

1956packardpanther.com/Panther/images/19 ... _Craig_FrontQuarterView20101125.jpg


Craig

In the greater scheme of things, custom pistons are not a big expense. Egge cast .030"s are $400 and any bore custom forged pistons are $800. That's only 10% more on a full custom engine build.

It has been pointed out before, but the Packard V8 block has the same 5" bore center as the 500" Cadillac V8, so certainly feasible for S-P to have built a 500" Packard V8. The main bearings would have had to be enlarged to at least 3" diameter for sufficient crankshaft overlap.

jack vines

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.