"hate this piston design"

Last week I was going to sell the crank, rods, pistons, fresh machined 0.030 over RB block to make a 493, and a local buyer informed me that his mopar consultant 'hates' this piston design.

I am a curious why these won't work in an 87 octane street car RB stroker application.

Sorry the pics are sideways... technology has defeated me on fixing that...

Thanks
Craig

I have heard an engine builder say they don't like dished pistons they didn't elaborate why. With a quench pad, I don't see why they would be much worse than flattops?

For a low compression street engine what is wrong with them? What kind of pistons are they Cast, Forged, or Hypereutectic? Lot of guys don't like Hypereutectic type pistons, but for a street engine not an issue, most stock engines now have
hypereutectic style pistons, many old part number cast pistons have been replaced with hypereutectic style pistons. Just have to set a couple clearances different. Heck, I have used them with good success in mild drag engines.
next question is what kind of chamber? If it is a 906 style open chamber, I would not like them either, no quench, if using a closed chamber head then again what is wrong with them?

Pistons are forged 2618.

What head are those designed for? The step design looks like something for an open chamber cast iron head? I'm not sure why there is a step up and a dish on the same piston unless it was an attempt to get some quench with an open chamber head?
If you have a block, crank and rods for sale you might just sell that combo and let the buyer get their own pistons. Most people run TF heads these days so the stepped design isn't going to work.

If they were designed for open chambers there would be some kind of pop up dome right? These look like every other Big Block stroker piston which have a quench pad on the intake side, and a dish everywhere else. I would think a quench area around the spark plug would be beneficial, but what do I know, I'm a filthy street guy.

Looks like an ICON piston. Same design i use in a 511 with victor heads. I was told these are a very nice piston at an affordable price.

I used that type, forged step dish pistons (AKA reverse dome), all the time in BB pump gas stroker motor builds with close chamber aluminum heads that end up with between 10.25 to 1 and 10.75 to one compression ratios with no bad results or complaints other than the customer cars spin the tires worse with the new motors in them

They are what they are. Be specific about what heads they'll work with. Find another buyer.

I believe they are an older 440source stroker kit piston. I have read that they are/were supplied by Icon

Looking at it I bet he/they thought they were KB Hypereutectic.

Could be an ICON piston. The step looks weird but just could be the picture. If the top of the step is close to zero deck at TDC then there shouldn't be an issue running those pistons with a modern head. If the top of the step is above the deck height then it is designed for an older open chamber head. I can't really tell from the picture what you have. ICON used to make step pistons for open chamber heads but they weren't a very popular design.

My guess is they don't like the grooves and trough cut in the OD. The grooves (as noticed in the pic) seem to be carbon collectors. Also noticed in the pic it looks as if there is a sharp edge at the face/OD interface

Fundamentally, I like reverse dome/reverse step-dish type pistons…….. but I’m not loving the ring grooving on that particular set.

It wouldn’t keep me from using them though.

Icon shows the top ring land to be .350” from the top.
Is that how far down those are?

Could be. I wouldn't run those pistons either since the top edge is already eaten away. Looks like it was too thin and it just got eaten up by the combustion. Either that or the picture makes it look that way.

There is def something “not good” going on at the top edge.

What is the purpose of those grooves?

Obviously the best pistons ever.

I have heard them referred to as anti-detonation grooves however, I do not know if that’s correct

The grooves are a good idea, but it looks like the top groove was too high. Maybe a design error, maybe a machining error. I don't really know without seeing them. Sometimes pictures don't show everything.

I believe the pistons I have are just an older version of this one from 440source. This discussion now has me a bit curious....I am certainly not a professional engine builder, and have never had an engine assembled in my garage on a dyno. Due to covid parts shortages I have a not very good combination in my car: 440 +0.032 (yes...32 over) with very old style L2295F30 TRW pistons, LY rods, 75 cc Performer RPM heads, a Hughes "real 6 pack" cam, performer 440 intake (fits under a flat e body hood) and iron hp manifolds. It has sky high cranking compression, but I think it would probably be safe on an engine dyno up to 6000 rpm with 112 octane fuel and conservative timing.

If I can find a dyno around West Palm that would put up with my nonsense it would be amusing to make 3 pulls with this not so great ~12.1:1 440, then go home and put the same heads, intake, carb, exhaust manifolds, and cam onto this ~9.8:1 CR 493 with the 'hate' pistons and run it again on the same dyno to compare the results... does ~10% increase in displacement overcome ~20% lower static static compression ratio?

Thank you.

Thank you too.

Cranking compression would probably still be up there with the same cam I bet.

I called Icon about these pistons several years ago. For use with open chamber heads you can run the pad proud of the deck. On closed chamber heads you run them to zero deck.

They reduced the outer band as a way to increase piston volume while keeping the dish reasonably shallow.

That’s all it is.

i use an icon 836 with edelbrock 84cc heads that has the same basic design. i have good quench distance with a felpro gasket, compression is what i want for pump gas, and i'd buy another set if need be.