Piston ID Help.

Discussion of the 331-354-392 HEMIs.

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Rob
Posts: 208
Joined: Thu May 05, 2011 10:15 pm

Piston ID Help.

Post by Rob »

Hi. mart has been kind enough to locate some 331 pistons for me. Here is a picture of one. Looks like a Jahn's piston to me. Any idea on compression ratio? I think it's certainly safe to say it's higher than the 7.5 I currently have. Thanks yall. And thank you mart!

Image
wayfarer
Posts: 83
Joined: Sun Feb 26, 2006 4:16 pm
Location: Peoples Republic of Oregon

Re: Piston ID Help.

Post by wayfarer »

Jahns often put their name on the inside, so if it is bare then look for a number of some kind. It is obviously higher than 8.5 since they were flat-tops. If they will fit in your bore as you had wanted then hook up a rod and crank and check the down fill volume to determine dome volume. Easier to make a guess at that point.
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George
Posts: 692
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Location: Fl

Re: Piston ID Help.

Post by George »

I take it you didn't get them in the original box.
Rob
Posts: 208
Joined: Thu May 05, 2011 10:15 pm

Re: Piston ID Help.

Post by Rob »

No. I actually don't have them yet. I am working out a deal with the owner. I will probably go ahead and get them because surely they are over 7.5:1. lol As long as they aren't 12:1 or higher, I think I'll be ok.
George
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Location: Fl

Re: Piston ID Help.

Post by George »

If he has the box the CR is @ the bottom of the label, possibly curled under on the bottom of the box.
mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Re: Piston ID Help.

Post by mart »

George wrote:If he has the box the CR is @ the bottom of the label, possibly curled under on the bottom of the box.
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I doubt he has the box because, I'm pretty sure these pistons are used.

mart
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Rob
Posts: 208
Joined: Thu May 05, 2011 10:15 pm

Re: Piston ID Help.

Post by Rob »

I got me some pistons. Old on the left. New on the right.

Image
mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Re: Piston ID Help.

Post by mart »

Rob wrote:I got me some pistons. Old on the left. New on the right.
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NICE!!!! It looks like the domes are about a 3/16 of an inch or so taller than the original truck 'flattops'. Not much... but enough to make a noticeable difference in power output for sure. The small dome should be good for about 1.5 to 2 points over the stock 7.5 to 1 truck pistons. And being 354 pistons too, the 23 extra cubic inches over the 331, also won't hurt anything in the power department either!:D

mart
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Last edited by mart on Sun Jul 03, 2011 12:21 am, edited 1 time in total.
DHEMI
Posts: 100
Joined: Mon Mar 06, 2006 8:01 am

Re: Piston ID Help.

Post by DHEMI »

So wich pistons are you going to use?
Rob
Posts: 208
Joined: Thu May 05, 2011 10:15 pm

Re: Piston ID Help.

Post by Rob »

The one on the right.
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