92 5.7 Factory pistons flat top or dished.

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Hipster

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I never cc'd one but they're dished and also beveled around the perimeter. They add a lot of volume to the chamber. I'm guessing your trying to run numbers through a compression calculator which is extremely inaccurate without also knowing the deck height. If the heads are off you can cc the piston in the hole at TDC by running a little grease around the perimeter to seal it. This number will include the deck height volume so you add it in accordingly and enter zero for deck height.
 

PlayingWithTBI

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FWIU, stock TBI pistons are ~12cc, deck height is 9.025" (which gives you a total of 25cc with piston dish and down bore), and combustion chamber is ~64-65cc, depending on who you ask. Don't forget your head gasket too. YMMV

As @Hipster said, the best way is to cc them yourself.
 

MikeManer

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Guys I really appreciate your help on this. Hipster I'm trying to decide if I can run a set of NOS ZZ4 heads I've come across. This is going to be a low to midrange torque motor running on 93. If I could end up at 10:1 or less I'd be happy. GM claims the ZZ4 heads had 58cc chambers so I'll use the information you guys provided and see where I am. Thanks again.
 

Schurkey

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The '92 B-body got flat-tops. '92 C/K <7200 GVW got dished pistons. The difference was 9.6 vs. 9.25 compression. The evil part is that the pistons are down in the hole at least .025, and up to .030. Which means you're kinda screwed for a suitable head gasket. MAYBE you can use the coated steel-shim gaskets from Fel-Pro or Mr Gasket. They're on the order of .015--.020 thick, which puts you towards the large end of quench distance. Way better than the typical .040 composite gaskets, though. I couldn't use those gaskets on my Trick Flow heads, the combustion chamber was wider than the gasket opening. I had to deck the block and then use a gasket with a bigger fire ring.


The ZZ heads were aluminum, so they should tolerate an easy +1 on compression. If those heads have pushrod guideplates, you'll need hardened pushrods and non-self-aligning rocker arms. If there's no guideplates, you'll need self-aligning rockers but you can do without the hardened pushrods if the valve springs aren't too stiff. The existing heads should have self-aligning rockers.

And, of course, the existing intake manifold won't fit. The center two bolt holes on the ZZ heads is at the "regular" angle, instead of the more-upright angle of the TBI heads.
 
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L31MaxExpress

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Ran ZZ4 heads on my G20 van years ago. Used the stock intake after grinding the bolt holes and getting some tappered washers made for that exact intake bolt angle swap. Ran the same intake on both a 601 headed 305 and the 601 headed 355 before that. My 601s were about 51cc.
 

Erik the Awful

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I put these in the Edelbrock C3BX I put on my TBI-headed cheap rebuild. https://www.summitracing.com/parts/pfs-52110

I'm guessing that if you flip them around they'll adapt a newer manifold to older-style heads.

I had to grind out the bolt holes to fit them, and if you fit them too tight people report they crack.


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L31MaxExpress

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I put these in the Edelbrock C3BX I put on my TBI-headed cheap rebuild. https://www.summitracing.com/parts/pfs-52110

I'm guessing that if you flip them around they'll adapt a newer manifold to older-style heads.

I had to grind out the bolt holes to fit them, and if you fit them too tight people report they crack.


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I used these. They came with the Weiand 177 I put on my TBI 350 G20 van in the mid 2000s. Pretty steep price now but never had one come apart. With some scrap metal, a skill saw with a metal blade, a drill and a bench grinder they could easily be replicated. It is just a tapered wedge with a hole drilled in it. Take your bar stock, grind the end of it at an angle, cut it to length, drill your hole, rinse and repeat until you have 4 of them.

 

Schurkey

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I've seen older-style intake manifolds that have been ground to fit the more-upright bolt angle of the TBI heads. Got one in the shop right now.

When I looked at doing the opposite--taking a manifold intended for the more upright bolts of the TBI heads, and grinding them to fit the old-style manifold bolt angle, it seemed to me that the stock TBI manifold didn't have enough material to make that work. Which is why I didn't use the TBI manifold on my earlier-style heads.

I am, therefore, really surprised to read that L31MaxExpress managed to do what I gave up on. I feel kinda silly.
 
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