7120 Not the Best Head Casting?

[JeepFamily]

When we first started building our 4.6 Stroker we found a common consensus that the 7120 head was the best. We hunted one down and it's now sitting on the bench rebuilt and nearly ready to install. after looking deeper into the air flow data published on various web sites, the benefits are not so obvious. when comparing the 7120 to the 0331 I find that the 331 out outperforms above a lift of 0.250" lift for the exhaust and 0.450" for the intake. It is surprising they are this close and the curves actually cross?? How much does this affect overall performance and are the aftermarket camshafts with high lift really the way to go when choosing the 7120??? I guess another question is how accurate is the data? Are all the tests performed under the same conditions??? THe 7120 intake seems to flatten out after 0.400" lift with any further valve movement having no improvement. The head seems to choke after 0.400"?? Thoughts, what do you think??

[Antifreeze2]

Maize did flow work on his head before and after porting - 94 7120
Before
0.050" 28.9 20.6 70.9%
0.100" 50.4 40.3 79.9%
0.150" 81.5 61.2 75.0%
0.200" 101.7 76.3 75.0%
0.250" 128.7 96.6 75.1%
0.300" 151.4 111.8 73.8%
0.350" 166.8 121.7 72.9%
0.400" 189.3 131.2 69.3%
0.450" 190.2 138.6 72.9%
0.500" 191.7 140.2 73.1%

After
Lift Intake Exhaust % Relation

0.050" 32.3 21.8 67.6%
0.100" 57.9 49.7 85.8%
0.150" 90.6 68.7 75.8%
0.200" 122.0 91.8 75.2%
0.250" 152.1 111.1 73.1%
0.300" 176.8 127.0 71.8%
0.350" 199.4 143.1 71.8%
0.400" 214.5 153.9 71.8%
0.450" 220.2 162.5 73.8%
0.500" 225.5 168.5 74.7%

The port work opens it up a bit

[JeepFamily]

interesting, the ported numbers are slightly above 0331? There are multiple sites that report flow numbers for various castings however they report the same data. Even the narritive is identical so there is only one source other than the one you provided. Not sure who originated the other data?

[Cheromaniac]

You'll find that the flow numbers will vary even for the same head depending on who does the measurements. It's a bit like comparing dyno numbers. The only way to make a proper comparison of different heads is for the same person to do the measurements using the same equipment and methodology.

[JeepFamily]

Thank you for the clarification. are the stock valves and ports for the 7120 the largest? I understand one benefit of this casting is the downward angle of the ports allowing better flow? Any further help you can give in understanding why the 7120 is as good as it is would be helpful.

[Cheromaniac]

The valves on all 4.0 heads are 1.91/1.50. The 7120 and 0630 heads were best for airflow (intake ports were placed higher in HO head than in Renix head). The 0331 heads have smaller exhaust ports.

[Newcomerracing]

7120 casting is the best 'all around' casting that I have tested and ported. The port height, cross-section, wall thickness, and casting shift issues are the consistently the best. The 0630 head sometimes has a much lower intake port opening. O331 castings are a good design to start the porting process just to thin and failure prone. Here are some flow numbers from one customers 7120 head at 28" on a superflow flow bench:
Stock: 1.91"1.50" Ported: 2.02"/1.60"
.100"-67/53 .100"-83/70
.200"-128/94 .200"-146/120
.300"-178/123 .300''-193/160
.400''-210/144 .400''-235/186
.500''-215/156 .500''-268/195
.600''-215/161 .600''-276/198
This is not representation of the best numbers of all time just an example of good streetable/race port work. Even with big ported 7120 heads that were known to be thin after porting I have not seen one crack, street or race.

[JeepFamily]

What spurred this post was analysis of available flow data of unmodified heads. The flow results showed that the 7120 was not the best. Cheromaniac noted that flow data is incredibly variable making the comparison unreliable. Newcomerracing, you bring a new perspective indicating the 7120 is a better casting to start a porting effort from. Good information thank you.

[Cheromaniac]

The flow results showed that the 7120 was not the best.

Actually the opposite is true. The 7120 heads ARE the best. I know that the 0331 heads outflow the 7120's at higher valve lifts but since the valves (when open) spend the longest duration just off the seats, it's the bigger low lift flow numbers of the 7120's that are going to provide the best performance.

[JeepFamily]

The consensous I get is the 7120 is the best for flow and now casting as well. What we need is some reliable flow data for the 7120, 0630 and 0331 from the same bench, at the same conditions, same lift, etc. to demonstrate actual flow differences. My son and I have a 4.7 stroker using the 7120 head and we are very happy with its performance.

[Newcomerracing]

Just remember people don't race flow benchs, they're merely a tool. Just because on head is better or worse on a flow bench does not represent the entire picture or if it will make more or less power. Add things like wet flow, reversion, chamber design, header design, piston design, intake design, cam design, etc. It can be very easy to make power yet very complicated if you take all know parameters into the equation to come up with a package that is well suited for your application. Comparing 7120/0630/0331 heads in stock form is simply splitting hairs, they are all pretty good for a factory head, thats why they all make roughly the same power unless modified.

[I6FAN]

Anyone have any experience with the Alabama Cylinder Head (ACH) heavy duty casting? I've heard that it is a heavy duty replacement for the preTUPY-crack prone head (supposed to be thicker). The attractive thing about the 0331 head is the raised runner exhaust port which is the achilles heal of the earlier heads. If the ACH head is thicker, to allow for more aggressive porting, this head just could be the deal... I do agree, it would be great to get some real data on all heads both stock and modified on same flow bench/set-up.

[showtime3492]

Anyone have any experience with the Alabama Cylinder Head (ACH) heavy duty casting? I've heard that it is a heavy duty replacement for the preTUPY-crack prone head (supposed to be thicker). The attractive thing about the 0331 head is the raised runner exhaust port which is the achilles heal of the earlier heads. If the ACH head is thicker, to allow for more aggressive porting, this head just could be the deal... I do agree, it would be great to get some real data on all heads both stock and modified on same flow bench/set-up.

This is what i run. I bought it about a year ago havent really had the chance to road test it yet. I wish i would have just kept my 0630 though...Maybe someone will trade me

[JeepFamily]

Here is the original chart that prompted me to start this topic, sorry for the delay. It is plotted from data I've found on the web. In this version I compare exhaust and intake flow for castings 7120 and the newer 0331. For intake flow the 7120 performs better until valve lift approaches 0.475 inches while the 0331 exhaust excels above valve lift of 0.280 inches. This is confusing to me since several people have blogged that the 0331 suffers from low exhaust flow. My understanding is that the 0331 exhaust flow was intentionally reduced to improve emissions. The chart brings this into question. Anyway I thought this would be interesting. I've included the 4th order polynomial fitted equations for any geeks that may be interested.

[Cheromaniac]

This confirms what I said in my last post. Flow numbers above 0.50" of valve lift are irrelevant anyway 'cause most aftermarket Jeep I6 cams won't even reach that lift number.