Need help Identifying 340 pistons

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coloradohill

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I bought a '69 340 about a year ago that was said to have approx. 12k miles since a rebuild. The previous owner acquired it with a car he bought and really didn't know many details of the engine. He did say it is 11;1 CR. I installed it and ran it this past summer and just pulled it today for some upgrades this winter. This looks to be a stock bore and the pistons are approx. .010 above the deck. I'm trying to calculate CR for cam selection. Any help is much appreciated! Thank you all.
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Those are the later 340 pistons. The early ones only had two eyebrows. I'm not even gonna get into "what year" the break was, because everybody always argues, but that's what you have.
 
The chamber volume would have to be really small to get 11:1 out of one of those. The early style two relief piston .023 out of the hole and a FelPro 2003 gasket will just get over 11:1 with a 60cc chamber.
 
RustyRatRod said:
Those are the later 340 pistons. The early ones only had two eyebrows. I'm not even gonna get into "what year" the break was, because everybody always argues, but that's what you have.
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Thanks Rob, any idea
Garrett Ellison said:
The chamber volume would have to be really small to get 11:1 out of one of those. The early style two relief piston .023 out of the hole and a FelPro 2003 gasket will just get over 11:1 with a 60cc chamber.
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It had x heads on it, I recently purchased Edelbrock RPM Performer heads (65cc) and want to calculate CR for cam selection. Thanks!
 
Looks like a sealed power 428P cast piston. I haven’t been able to find the piston head volume for those yet.
 
Garrett Ellison said:
Looks like a sealed power 428P cast piston. I haven’t been able to find the piston head volume for those yet.
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Me either. I just "went with" some real similar 4 eyebrow pistons and used 12 cc's. Using that, the .010" outta the hole and the FelPro blue gasket at .039" I got 9.4:1. That's probably real close.
 
If it’s .010 above deck it will have replacement pistons because of the 4 valve notches. U should be pretty close to 9.5 or so. Clean the top of the piston off and see if there is any numbers on them. Kim
 
I dont think those are factory 72+ 340 pistons. Something just does not look right to me. I have some NOS ones out in the garage I will take a look at.
Are those slightly in the hole or are they above deck?
 
Looks like you have it figured out. For reference, here is a pic of a stock mopar 72-73 340 piston. Its just a flat piston with 4 reliefs fly cut into it. No bevel on edge and no dome.

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The 72 piston will not have a positive deck height. It’s has a ch of 1.74 vs the earlier ch of 1.82ish.
 
RustyRatRod said:
Me either. I just "went with" some real similar 4 eyebrow pistons and used 12 cc's. Using that, the .010" outta the hole and the FelPro blue gasket at .039" I got 9.4:1. That's probably real close.
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Yep, I get 9.5 with 10 cc eyebrows, .039" head gaskets, .007" above deck, and 65 cc head chambers.

OP, food for thought... With these pistons and deck height, there is no need to have the shallow open chambers of those particular Edelbrock heads. The 63 cc chamber heads will work with these pistons using a .050" thick Felpro 8553PT head gasket result in the same static CR, and you will have a tight quench gap to help combustion and add some resistance to detonation if you get aggressive with this. So if these can be exchanged, IMHO that would be to your advantage.
 
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