Piston ID Help.

Discussion of the 331-354-392 HEMIs.

Moderators: TrWaters, 392heminut, scottm

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

Piston ID Help.

Post by Rob » Wed Jun 01, 2011 3:25 pm

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: 77
Joined: Sun Feb 26, 2006 4:16 pm
Location: Central Ory-gun

Re: Piston ID Help.

Post by wayfarer » Wed Jun 01, 2011 4:30 pm

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.
www.qualityengineeredcomponents.com
Early Hemi Parts and Pieces,
Complete machine shop services
Trans Adapters, Tech info

George
Posts: 643
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

Re: Piston ID Help.

Post by George » Thu Jun 02, 2011 12:36 pm

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 » Thu Jun 02, 2011 12:40 pm

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
Posts: 643
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

Re: Piston ID Help.

Post by George » Thu Jun 02, 2011 4:59 pm

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 » Sat Jun 04, 2011 10:39 pm

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

mart
=======================

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

Re: Piston ID Help.

Post by Rob » Fri Jul 01, 2011 3:10 pm

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 » Fri Jul 01, 2011 4:09 pm

Rob wrote:I got me some pistons. Old on the left. New on the right.
------------------
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
==========================
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 » Sat Jul 02, 2011 7:20 pm

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 » Sat Jul 02, 2011 8:00 pm

The one on the right.

Post Reply