7120 Not the Best Head Casting?

[gmakra]

I just went through this a few weeks ago while doing a cam change I sent my head to have it checked and after the Magnaflux I found out it was cracked. I went down to the junkyard and got another 7120 head $35 later I found out it was cracked, got another 7120 head and the second head was cracked. I came to realize that good 7120 heads are becoming harder to find.

I went with an ACH head (Chinese casting) and while they list other heads the only one they are casting are the 0331 heads. I did a little research and found out that the casting has been beefed up in the areas that hey tend to crack. And yes the exhaust ports are much smaller the reason given to me was that the ports are smaller to keep the exhaust velocities high to help with emissions.

Surprisingly the casting seemed to be very high quality and after the install the but dyno says there is no difference.

I have an appointment at a dyno to do the fine tuning on the ECM in a couple weeks and if you want I can post the results.

[JeepFamily]

We built a 4.7liter stroker with the intent to turn it into a rock crawling stump puller. For this we chose an unmodified 7120 casting with a Comp Cams 68-232-4 cam. We are extremely impressed by the performance. We live next to the continental divide with an elevation of 6400 ft. The engine will pull our ZJ up the pass at 70 mph in overdrive! Better than our 02 WJ 4.7L HO V8!!! With this low rpm torque requirement in mind how would the 0331 casting head affect our performance? Would porting the head improve or reduce torque?

[JeepFamily]

I just went through this a few weeks ago while doing a cam change I sent my head to have it checked and after the Magnaflux I found out it was cracked. I went down to the junkyard and got another 7120 head $35 later I found out it was cracked, got another 7120 head and the second head was cracked. I came to realize that good 7120 heads are becoming harder to find.

I went with an ACH head (Chinese casting) and while they list other heads the only one they are casting are the 0331 heads. I did a little research and found out that the casting has been beefed up in the areas that hey tend to crack. And yes the exhaust ports are much smaller the reason given to me was that the ports are smaller to keep the exhaust velocities high to help with emissions.

Surprisingly the casting seemed to be very high quality and after the install the but dyno says there is no difference.

I have an appointment at a dyno to do the fine tuning on the ECM in a couple weeks and if you want I can post the results.

Excellent information. It's actually surprising the smaller exhaust ports are equivalent! I wonder if, as one remains true to the low rmp/high torque build, port flow is less important while port velocity is something to monitor? The local jeep shop swears by port velocity but has no performance data to offer. There is however a lot to be said for experience. Please post your dino results when available as that would be very helpful in clearing up the benefits of various options!

[gmakra]

Heads (2).jpg

Here you the the 7120 head compared to the 0331 head you will see the difference in the exh ports.

[SilverXJ]

0331 vs 0630 ports, red is the 0630:


0331 head exhaust gasket over 0630 head: