Difference between X and O Heads? - Moparts Forums

Register Log In Moparts Forums Moparts Question and Answer Difference between X and O Heads?

Print Thread

Difference between X and O Heads? #2835965 10/22/20 08:32 AM 10/22/20 08:32 AM
Joined: Apr 2012 Posts: 1,562 Macomb, MI V vinnyd76 OP pro stock
vinnyd76 OP pro stock V Joined: Apr 2012 Posts: 1,562 Macomb, MI	Interested to learn more about the difference between "X" and "O" 340 heads (thought there maybe "U" heads too?). I know "J" Heads are a later model head (71+).

Re: Difference between X and O Heads? [Re: vinnyd76] #2835991 10/22/20 09:46 AM 10/22/20 09:46 AM
Joined: Feb 2015 Posts: 2,070 CA C crackedback top fuel
crackedback top fuel C Joined: Feb 2015 Posts: 2,070 CA	o j u z are all the same. x has value to the restorer, got to have that letter crowd. They are all basically the same except for minor differences in the ports which are usually not noticeable in performance on any engine. I have a 70 car that came with an x on one side and a J on the other.

Re: Difference between X and O Heads? [Re: crackedback] #2836010 10/22/20 10:37 AM 10/22/20 10:37 AM
Joined: Jan 2003 Posts: 14,491 So. Burlington, Vt. F fast68plymouth I Live Here
fast68plymouth I Live Here F Joined: Jan 2003 Posts: 14,491 So. Burlington, Vt.	In my testing X heads flow the best ootb. They have a better shape to the intake port SSR, and as a result I also find them to be the easiest to get the flow numbers into the 250-260-270+ range. On a totally stock 340 package, I can see where there would be essentially no performance difference. The main difference between them is, the X head intake port was designed around using only a 2.02” valve. The J head intake port was revised(primarily in the bowl and SSR area) so it could facilitate the use of either a 2.02” valve....... or a 1.88” valve. 68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads

Re: Difference between X and O Heads? [Re: fast68plymouth] #2836352 10/23/20 03:34 AM 10/23/20 03:34 AM
Joined: Jan 2003 Posts: 6,379 Abilene, Texas F fastmark master
fastmark master F Joined: Jan 2003 Posts: 6,379 Abilene, Texas	Originally Posted by fast68plymouth In my testing X heads flow the best ootb. They have a better shape to the intake port SSR, and as a result I also find them to be the easiest to get the flow numbers into the 250-260-270+ range. On a totally stock 340 package, I can see where there would be essentially no performance difference. The main difference between them is, the X head intake port was designed around using only a 2.02” valve. The J head intake port was revised(primarily in the bowl and SSR area) so it could facilitate the use of either a 2.02” valve....... or a 1.88” valve. This is what I have heard from some old mopar stocker racers.

Re: Difference between X and O Heads? [Re: fastmark] #2836761 10/23/20 10:25 PM 10/23/20 10:25 PM
Joined: Mar 2003 Posts: 18,678 Fresno, CA Jim_Lusk I Live Here
Jim_Lusk I Live Here Joined: Mar 2003 Posts: 18,678 Fresno, CA	There are also some physical differences below the exhaust ports where the head bolts go. The footprint is wider on the later heads than on the X heads. J followed by X heads. Note the area of the exposed head bolts. Last edited by Jim_Lusk; 10/23/20 10:26 PM.

Moderated by Al_Alguire, Hotwheelsjr, moparts, not_a_charger, RangerDan440, tboomer

Hop To

Powered by UBB.threads™ PHP Forum Software 7.7.1