I am putting together a 340 stroker. The block will be .020 over with a 4" crank and 6.123 rods. I have ported eddy closed chamber heads that measure 66.4cc. I plan to use a .039" thick Felpro head gasket. I want the CR to be around 10.5:1 or a little more. I am going to use a cam that will bleed off some pressure so I think this would work well with pump gas in a relatively lite 69 barracuda notchback. It looks to me like all the stocked pistons for a 4" stroke SB are either flattops with about 5cc or dished with about 20cc. With a zero deck, the flattops will be about 11.6:1 and the dish pistons will be under 9.9:1. Has anybody put together a combo similar to this and found a piston that will get the compression up a bit?

What size is the cam exactly? Do you mind running super unleaded? If you run std unleaded, and the cam is milder (say under 240°@.050) I would go with the dishes. If you dont mind running super, or, your cam is larger (say over 255°@050) then I would go flat tops. Flat tops will always be the preferred for me. But soemtimes you can't use them. All depends on the whole package, and you left out a crutial bit.

I am in the process of putting together a stroker 340 and ran into the exact same dilemma. Originally I had purchased flat top pistons however, I ended up returning them for dish pistons. After all of the machine work to the block was completed and prior to returning the piston, I considered trying to make it work with using a thicker head gasket, enlarging the head chambers, tulip valves, and milling the pistons.
I came to the conclusion that the dish pistons would be fine for my application (street motor, w/hyd cam) I was okay with the lower compression.

Is all of your machine work done to the block? Have you checked the specs of other piston manufacturers? The other option are custom piston.

Good luck....

For another hundred $ you can probably get the dish cut to whatever cc you want. You've gone this far, don't compromise over something like that. Ask your piston supplier what it would cost to get the custom dish, they'll probably know real fast. Compression equals horsepower and efficiency, to be thrown away grudgingly.

R.

Do you really think your going to notice a difference between 9.9:1 and 10.5:1? I would go with the 9.9, the cubes will more than make up for whatever loss you have in comp.

I am building a 414 SB stroker (.020" 0ver 340 block). I am going with KB745 pistons with 20.5 dish, Felpro 1008 .039" head gasket with 4.18" gasket bore, and closed chamber eddie heads milled to 62 cc. This will give me 10.3:1 compression. I could go with Cometic .036" with 4.060" gasket bore to get 10.47:1 compression. But 10.3:1 will be plenty to make good power on pump gas premium. You can play with some numbers with this calculator:

http://kb-silvolite.com/calc.php?action=comp

A few years back, did a 406" for my '74 Duster. Iron 360 heads, 10:1 CR, flat tops, 214/224 @ .050, .470/.504 Engle cam, 340 rods, cast crank, Hooker street headers, Performer intake & Thermoquad by Demonsizzler on this board. Killer torque, very ample power, perfect driveability, plenty of power-brake vacuum, BUT marginal on 91 octane over 75 degrees ambient temp as far as detonation. Had to pull most of the vac advance out of it. 17MPG freeway with 3.21s & 275/60R15 tires, factory AC works fine. It also sounds great with Flowmasters, 2.5" pipe & factory tips. Not too loud, but it definitely has authority.
Doing it again, I'd run less CR or aluminum heads, or a little more octane. Your car is most likely lighter, though, and possibly less octane sensitive, but likely not by much.
One thing I learned the hard way is the MP 4.020 cast pistons were actually SB Chevy pistons (fit Chevy rods) and the pin bosses had to be machined for the Mopar rods. I should have gone with JE like I usually do.
It has the wide Milodon 8-qt pan (had to notch the K about 1", pretty much removing the flange).

Thanks for the help/advice. Have not finalized the cam choice completely, but will use a cam in the 245 to 250 range at .050". Am planning to run premium unleaded. Leaning towards a hydraulic roller that is 246/252@.050". I am considering custom pistons. Any brand recommendations?

I used Diamond Pistons for my last two stroker motors. When I was considering my options they mentioned they'll make me custom pistons. I think I was looking at 3 to 4 weeks turnaround and somewhere around $650-$750.

To Diamond's credit they accepted my flat top piston which I purchased a year earlier and exchanged them for a lower compression dish piston. I only had to pay a small difference in price so I was happy since quality pistons are not inexpensive.

I believe the JE, Wiesco, Ross and several others will make you a custom set if you decide to go that route.

Good luck....

With the cam you are planning to run combined with the closed chamber aluminum heads 10.5:1 compression would be ideal for a pump gas engine. Custom pistons would be a good way to go if you already have the heads and don't want to mill them.

diamond P/N 51411 is a 9.3cc dish for a .030 over 340 with a 4" stroke. They list at 10.6:1 with a 65cc chamber. realistically, doing the calcs, it's going to be closer to 11:1. one thing you could look at doing, if you run into some detonation would be to water inject it, like turbo guys do.

Diamonds woudl be my first choice. If you need to get .020 over, your custom anyway, so any dome(meaning top) design is doable. If you go .030 over, they are a bit cheaper. With the roller cam idea, I would go dished. Just my opinion, but I'd rather err to the side of street and manners than worry about careful tuning or fuel. Go dish, bring them to the deck, and run it.