Piston dish question
 

Hi all,

Just curious how much dish some of you are running, and what’s the most you’re cutting out? Anybody at or near 30cc?

I’m considering the options on my build and of course a major factor is cubic inches versus combustion chamber size. Still teetering on buying aluminum heads or using my ported 62 iron heads, if I use the iron heads and Butler’s 471 stroker assembly withRoss pistons (400 block .030 over) a 30cc dish calculates out to 9.4:1, which ‘should’ work with 91 pump gas. Butler says 30cc is doable, but pushing it. I don’t know if pushing the envelope is a good thing to do or not in this case? But if it works without issues, I just might. Thanks for any feedback!


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Ross pistons with 27cc dish in my 8.82:1 421 HO (429 cu. in.), 76cc 9770716 heads, pistons .007” to .008” above the deck and .045” Butler head gasket.

http://i137.photobucket.com/albums/q...0Rebuild18.jpg

So Bart, that's leaving you a .035ish quench distance???

.037” to .038” which is fine for my street cruiser that will rarely see 5K rpm.

"Pushing it" in what way? What does that even mean?

I can't see any reason why a dish of that size should create a problem, as long as there is still a flat area around the outer edge of the piston to provide quench. The pistons b-man posted look fine to me.

If you order a custom piston from any piston manufacturer it should not be a problem. I've ordered 3 sets of custom pistons from Ross with dishes that ranged from 14- 22 cc, they call it a reverse dome.

Well you yourself ( the OP) needs to nail down the head thing because if you run a aftermarket head you want a 10.5 compression and do not need the dish at all!

Also in terms of using iron heads folks always seem to to leave out the the 1.5 CCs that reside in the ring land back clearance of the two compression rings and between the bore clearance and the 1st and 2nd ring,
You really only need a 28 CC Dish.
Add to that another 1.2 CCs of volume from your blocks valve notch at the top of each bore which many of even the 2 bbl blocks have .
It takes a .060” over bore to loose most of these notches!

A dish should not be a problem. Here is a 25cc dish I had machined in some TRW's so I could run my ported 670's on pump gas. I believe most people like the "D" shaped dish that a lot of new pistons will likely have.

38 cc dish Ross Blower slugs. Went a bit too much huh. Low 12s NA

I was told by Autotec that a dish can get too big and compromise the integrity of deck.They get around it by what he called a donut but have NO clue what that was.I did a 23cc dish in a 4.04 bore piston.Tom

If it works, it works! [emoji4][emoji1360]


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Not a dish, it’s a reverse dome. You know, it makes sense to me. I say something similar to my bank about my checking account. “I’m not overdrawn, I’m under deposited!” LOL


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I have some Ross 32 cc dish pistons, Its a generic dish. I bought them from Scott Brown, thought I was getting a mirrored dish for E heads. Contacted him about it and he assured me I would have n issues at 11.5 CR.
Called Ross and talked to them about it and was told when the dish gets large enough making a mirrored dish causes problems with piston integrity and weight. Thats what a tech told me and one of the top guys at Ross who was in the room confirmed it.

9.4 to 1 compression is LOW for one of these engines, especially with aftermarket aluminum heads.

Compression is power (torque) and moving up from 9.4 to 10.4 or so allows for 10 degrees more camshaft with zero negatives anyplace, and it will operated just fine with the same octane fuel.....FWIW......

Likewise, moving from 10.4:1 to 9.00:1 allows for low vacuum, barely able to cold idle, negatives anyplace, and it will operate just fine with 87 Octane....FWIW.

87 octane? You should be able to pee in the tank and be fine at 9 to 1 with that much camshaft!

Might want to offer that to the new administration as an alternative to getting rod of fossil fuel and going all electric. Lower emissions with urea instead of gasoline.......LOL....

The pistons im about to install in my 496 build have a 4.19 bore and 40cc dish...

SPEED SAFE, NICK

Is the remaining quench in a full dish like that effective? Couldn't you just run a flat top .050 in the hole?

Yep you can run it in the hole .050 with a .055" head gasket but do not complain when the thing has flame burn and combustion stability issues. I have already posted about this many times in the past.

A .055" thick Pontiac gasket that crushes to about .050" thickness is about as thick on the gasket as you want to go IF the piston is more than .012" below the block deck. You get into the .075" or higher "head deck to piston top distance and the engine starts having combustion and flame travel "bad events" in engines.
A proper dished piston with a circular quench surface and a .040 -.050 head gasket it a much better design.


Tom V.

Just some food for thought but I've only assembled and dyno'd one dished piston 455 variant. I had NOTHING to do with any of the choices, just hired to assemble it after the owner had a falling out with his builder.

It was a 400 block with a Butler stroker kit, cast steel crank, no names on the rods or pistons but they had a pretty big dish in them lowering the compression to around 10 to 1. I never cc's any of it, just put it together and carried it to the dyno. If you are wondering why it had dished pistons to get to 10 to 1 the original #48 heads ended up getting scrapped and the rotating assembly to lower the compression was bought and paid for and machining done. So basically just a swap to KRE heads with smaller chambers.

It didn't make nearly the power of similar engines I've carried to the same dyno. It was topped with a set of SD performance CNC ported heads and RPM intake. Initial pulls were around 490hp and 540tq nearly as I can remember. No where near the 550-560hp and 585-604tq we've seen from nearly identical 455 builds.

I messed around with timing and fuel, even moved the cam and things only got worse. One of those deals where making power wasn't even on the list of priorities but I did want to find out where it was coming up short, but never did. I sent it out of here never knowing where or why it wasn't quite up to par, but never did another dished piston 455 build.......FWIW......