Cyl Head Markings

[Texacoon]

I'm interested in stroking my current 4.0L engine ('88) and found a person who is selling a '91 4.0L engine head. I asked what stamp numbers were on the head the only markings show "HNI" and "92".

My question is this the engine head that has better flow than pre-'91 or later (Y2K) 4.0L heads?

[Mgardiner1]

viewtopic.php?f=27&t=241

7120 head (91-95) is fabeled to be the best "stock" flowing head. I don't think anybody has ever proved it on a flow bench though

[Texacoon]

http://www.jeepstrokers.com/forum/viewt ... f=27&t=241

7120 head (91-95) is fabeled to be the best "stock" flowing head. I don't think anybody has ever proved it on a flow bench though

I would have thought it would say 7120 not HNI 92? How would one know if it doesn't have the full marking?

[John]

Jeep heads are identified by a casting number on top of the head above the #4 exhaust port, on the manifold side.
John

[gradon]

0630 is just as good as the 7120 and now there is talk that the 0331(other than the crack-prone 2000) might be a good base to start a port and polish.

[Mgardiner1]

0630 is just as good as the 7120 and now there is talk that the 0331(other than the crack-prone 2000) might be a good base to start a port and polish.

Exactly why i would never swear that one is better then the next. Was just stating the "rumor" for the 7120. I think if all casting heads were reworked the same way, that they would not prove more then 1 or 2% gains/loss on a dyno, which would be undetectable to most people.

[SilverXJ]

0630 is just as good as the 7120 and now there is talk that the 0331(other than the crack-prone 2000) might be a good base to start a port and polish.

I wouldn't say that 2000 was the only crack proned year. I have heard that they fixed the casting in 2003.

[Alex22]

http://www.jeepstrokers.com/forum/viewt ... f=27&t=241

7120 head (91-95) is fabeled to be the best "stock" flowing head. I don't think anybody has ever proved it on a flow bench though

viewtopic.php?f=8&t=245&start=0

The 0331 head was flowed on a different day than the 0721 head, but it does show the trends of the heads.
IIRC the exhaust port on the 0331 head was raised from where it was on the 0721. I'm interested to see when the changes were made to correct the cracking issue.

~Alex

[John]

0630 is just as good as the 7120 and now there is talk that the 0331(other than the crack-prone 2000) might be a good base to start a port and polish.

I wouldn't say that 2000 was the only crack proned year. I have heard that they fixed the casting in 2003.

And they did it discretely to avoid further publicizing a issue with a pending class action suit. Not a good time to publicly say "We fixed the problem that caused your failures." We would likely need to autopsy a pre and post change head to find the changes.
John

[1bolt]

exactly what we're trying to do in the "0331 Head thread" in Tech. If anyone in here hasn't read it already go check it out we're trying to catalog any visible changes and arrive at some sort of consensus as to which 0331's crack and which don't... It seems safe bet that anything after 2004 or 2005 is an improved casting, but just when and how they improved it we have no sure clues about.