30cc Dished Pistons - Pontiac GTO Forum
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post #1 of 13 (permalink) Old 09-03-2013, 12:13 AM Thread Starter
 
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30cc Dished Pistons

I'm starting the build on my 1st ever Pontiac engine. I have a 455 with a set of 62 heads. My plan is to do a +0.030 piston and zero deck the block. I am going to reuse the crank and replace the connecting rods with either h or I beam forged rods. I am going to leave the 2-bolt mains but will stud them.

I have used the CR calculator at the wallace racing website and it looks like I'm going to need pistons with a 30cc dish to bring me in at 9.5:1. The problem is, I don't see anyone list these on the web.

Is this an 'off the shelf' item or will I have to have them custom manufactured?
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post #2 of 13 (permalink) Old 09-03-2013, 09:08 PM
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You're probably not going to find them unless you have them custom made, and maybe not even then. 30 cc's is a lot. Are you dead set on using those heads? What static compression ratio are you shooting for?

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post #3 of 13 (permalink) Old 09-05-2013, 06:47 PM
 
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Keith Black offers a 30.5cc dish Hypereutectic .30 piston. Part # KB371-030, at Summit Racing for $453.97 a set. Butler Performance offers Ross custom made forged pistons which are called reverse dome pistons, but at a much higher price.
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post #4 of 13 (permalink) Old 09-05-2013, 09:08 PM
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For forged, it's worth the cost. Personally, I'd never put hypereutectics in any engine I cared about.

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post #5 of 13 (permalink) Old 09-06-2013, 10:49 AM
 
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Quote:
Originally Posted by BearGFR View Post
For forged, it's worth the cost. Personally, I'd never put hypereutectics in any engine I cared about.

Bear
I am not for or against them, curious what is your objection? As long as silicon is held low?? or is it just cast vrs forged?
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post #6 of 13 (permalink) Old 09-06-2013, 11:38 AM
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Forged are much stronger and will survive pre-detonation far longer then the cast ones.
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post #7 of 13 (permalink) Old 09-06-2013, 12:01 PM
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Quote:
Originally Posted by the65gto View Post
I am not for or against them, curious what is your objection? As long as silicon is held low?? or is it just cast vrs forged?
Hyper's are the middle ground between conventional cast and forged pistons. They are a little stronger than conventional cast pistons, but they're not nearly as strong as forged ones. Their slight increase in strength comes from manufacturing tricks to get the silicon content up to around 16% to 19% as opposed to around 12% for regular cast --- the increased silicon content is the definition of hypereutectic.

What is touted as the "advantage" of hyper's is that their dimensions don't change with temperature as much as those of forged pistons, so when running hyper's you can build to tighter clearances and avoid the noise ("piston slap") in a cold engine that you sometimes get with forged pistons (because they require looser clearances). Once an engine with forged pistons warms up to operating temps, that problem goes away.

However, hyper's aren't as strong as forged and almost as important: they don't "bend" - they break.

So, when you run hyper's what you're doing is gaining a few minutes of slightly quieter operation while the engine is warming up and you're also saving on some cost, but you're also making a significant sacrifice in strength and toughness, and you're also taking a risk with what can happen in "unusual circumstanced". (Remember, cast and hyper's break, they don't "bend" like a forged piston can.)

I dunno about ya'll, but having an engine that is "quieter during warmup" isn't exactly high on my list of prioritiies..
However, strength, toughness, and longevity are VERY important to me so that's why I said..

"Personally, I'd never put hypereutectics in any engine I cared about."



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post #8 of 13 (permalink) Old 09-06-2013, 12:11 PM
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I agree with Bear and Rukee. From what I've read and experienced, forged pistons are my only choice, period. Hard= brittle, and brittle breaks.
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post #9 of 13 (permalink) Old 09-06-2013, 10:47 PM Thread Starter
 
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Sorry for the break; hectic work week followed by a day without internet.....

Bear:
Shooting for 9.5:1. Yes, I'd like to use the heads since 1) I already have them and 2) I already have them back from the machine shop.

PontiacJim:
I saw the Ross pistons and will most likely go that route. I'll just have to put in a call to Butler Performance and see what they have to say.

I started out wanting to build a 400 but had the 'worst' block for a rebuild (557) and after talking to a few people it was apparent I wouldn't be spending that much more money building a 455 over the 400.

I appreciate all the feedback and I'll let you know how things work out. I'm still seeking out a machine shop locally so I'll be spending tomorrow tearing down the 455 (got it today) and getting it ready to send off.
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post #10 of 13 (permalink) Old 11-18-2014, 07:54 PM
 
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First time here and not sure if proper to revive this thread, but it describes where I am now... down to the 62 heads (which I learned I have to check to see if they're 72 or 75 cc).

This thread says no hypereutectic pistons, about which I agree, but says forged pistons will slap when cold - but slapping only happens with Ross/other pistons that are made from 2618 aluminum, right? but not if they're made from 4032. Butler says the Ross pistons are 2618 T6 but I don't know what T6 means (less expansion?). I assume Butler sells a LOT of them, and I can't imagine so many people are out there with engines that slap when cold - there's also cylinder and piston wear that comes from slapping during each heat cycle.

Butler talks about Mehle dished pistons on the rotating assembly page - 4032 aluminum with 22 cc dish. I used Summit's calculator and with 4.155" bore, 4.25" stroke, 72 cc chamber, 22 cc dish, (assuming) .02" deck clearance, and (need to get) a .06 thick gasket yields 9.44:1 CR.

Does this CR sound reasonable and are forged 4032 aluminum pistons the best choice? My machine shop said 2618 is not good for a street engine.
This Mehle article describes differences.
Which Mahle Piston Is Right For Your Engine? - High Performance Pontiac Magazine

I assume 4032 was available when this thread started.
It's odd that I don't see any dished Pontiac piston in Mehle's catalog.
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