doing a dirt cheap rebuild on a 400 big block. would like to run 87 octane if possible, but would like to see compression in the mid 8s with stockish smogger heads. IS there a piston out there that will do this? Never going to be a drag motor. Trying to replicate 383 Magnum performance with a little less compression.

This engine is going in a 4x4 truck. thinking MP P4452783 or maybe a Comp XE256H.

Look for stock replacement pistons from Badger or Federal-Mougal.
The trick here is to pay attention to the pistons height. If you can not find a slug slightly taller, have the machinist deck the block or heads a bit. You'll have to crunch numbers with him to finalize the exact comp ratio.

Here's the math:

4.342 bore 3.38 stroke turns into 400.4
Each cylinder = 50.05 = 820.5cc

Divide by r-1 to get volume above the piston for compression ratio r.

820.5 / 7.5 = 109.4cc

Assume 88cc head, 5cc gasket steel shim

16.4cc needed.

(16.4 / 820.5) x 3.38 = 0.068 Piston top that far down in the hole.

9.98 - 6.358 - (3.38 / 2) - 0.068 = 1.864
That's the compression height to give you 8.5:1

Both F-M and Silvolite have pistons with comp height or 1.812 or 1.813 giving you 7.72:1.

The KB 240 piston has a 1.908 comp[ height with a 8cc valve notches, gives their calc 8.9 CR with 88cc head. Campbellenterprises has them on sale for about $450 a set.

By the time you do all the milling and buy your pistons, minimum $225 for NOS on the 'bay, you have about paid for the KBs.


Otherwise you're SOL.

R.

Dog days, helpful as always!

There are some 440 Cast pistons(cheap) with approx. 1.912 Compression height. A 440 with .040 overbore = .018 overbore in a 400. The only thing that might be an issue is the weight. That'd be .022 below deck and as a flat top (no reliefs)would make about 8.99:1 Comp. Just some more food for thought.

These? http://www.summitracing.com/parts/slp-424np60/overview/make/chrysler

I think I have some .055 or 0.060 over 2266s, I would be interested in using them up

My catalog says those 2266's are 1.991 CH which will have them protruding above the deck, not to mention valve clearance issues. The pistons in the Summit link above are like what I was talking about. I believe that Comp. Height can be had in some other brands. Should be able to pick up a set on Ebay for around $150 or so.

Quote:

---

I think I have some .055 or 0.060 over 2266s, I would be interested in using them up

---

Well, feets, I would disagree with you if he's using those horrible open chamber Mopar bigblock heads. They are very octane sensitive and they do have problems with detonation at 9:1 and above if used with a street type camshaft. We've heard this on the board before.

R.

I have several sets of 516s. Should I put bigger exhaust valves in and run those instead?