7120 vs 0331 head

[dwg86]

I have read many times that the 7120 head has a "lazy" port design, and the 0331 has better shaped ports. Does anyone have any cut-away pics of the heads to show where the ports are lazy and differances in the port designs?

[gradon]

Looks like I have a 0331 that won't be used that can be sacrificed to the bandsaw--that'll show us exactly where the weak casting is.

[seanyb505]

Looks like I have a 0331 that won't be used that can be sacrificed...

The Jeep gods approve, and do the banana dance

[Plechtan]

Check out this thread before you do too much cutting

http://www.jeepstrokers.com/forum/viewt ... ?f=5&t=735

[gradon]

I wasn't gonna do the cutting--I was just offering it up to be cut(ahem 5-90, unless you've already done so). That link shows a 7120 head, which is near identical to a 0630 head. I have the 0331, vastly different from those two. It ideally would be cut b/t 3 and 4 to see where the weak casting is.

[5-90]

Not yet - I don't have a 0331 head to work with (just some 2686 heads, a 0630 head, and a 2685.)

Ideally, I'd like to get a 1999-2001 0331 and a 2002-2007 0331 so I could compare the two areas and see what changed, but that's going to take time I'm sure (bloody!)

[TurboTom]

Not yet - I don't have a 0331 head to work with (just some 2686 heads, a 0630 head, and a 2685.)

Ideally, I'd like to get a 1999-2001 0331 and a 2002-2007 0331 so I could compare the two areas and see what changed, but that's going to take time I'm sure (bloody!)

I would give you mine...but it's too busy running in the 10's

[1bolt]

In brief, the 0331 head and manifolds, were redesigned by Rick Mudge (who ported Garth Hill's NHRA 4.0 drag racer) to do a better job in the RPM range that Jeep 4.0's are intended to operate. The intake manifold is longer (11.5" long runners compared to about 9"), more equal runners and feeds the slightly higher, and slightly larger intake ports of the 0331 head. The cast iron exhaust manifold has longer primaries (10" on average compared to 6" average on the header style factory exhausts) and matches up to the 0331's exhaust ports much more closely than previous tube headers (which means better scavenging).

IMO you can't talk about the 0331 head without also talking about the manifolds which are both better than previous factory pieces.

The 0331 intake ports flow better than any other HO head in my experience, Both I and Alex22 have flowed the 7120 (or 0630, they are the same) and 0331 and both of us found the 0331 to have higher CFM on the intakes. There's some numbers here if you do a search.

The exhaust ports are MUCH smaller but flow only a little less than older HO heads, this is because the area that was "filled in" so to speak to make them smaller was a "lazy" area (the floor of the port after the short side radius) NOSIGMA's velocity maps show this area on 7120 heads plain as day. And he also talked about how he'd love to be able to fill in the floor of the port raising it and increasing exhaust gas velocity... Looks like Rick Mudge did this, raising the floor makes the port smaller, but it also makes the short side radius much more gradual. He also gave the new exhaust port a trapazoidal crossection where the roof is smaller than the floor which has also been found to be a more ideal shape for the 4.0 heads, even the intakes have a small amount of trapezoidal narrowing towards the roof.

I used EA pro to sim the 99+ intake, the exhaust and the 0331 head as single mods (retrofitted to an older HO) and as a full system (in other words like a 99+(WJ) or 2000+ (XJ and TJ) factory engine without the factory emissions/MPG camshaft, and the emissions tuning (and without the pre-cats)...

I've never posted the numbers up here because I think no one will believe they are realistic... And even if Engine Analyzer Pro is a great engine simulator used by race engine builders, it might be wrong, and I might be wrong to believe it.... I'll just say this... I believe the SYSTEM (not only the head) without the factory emissions tuning and fuel economy cam is good for a LOT of torque over an earlier HO.

A lot of this info can be pieced together by reading the sticky thread on head porting (collected work of NOSIGMA).

[SilverXJ]

How did the 0331 head fair with an aftermarket header for the earlier head and the new manifold vs. the same but with a 0630 head? Besides the cracking in the earlier 0331 heads, are there any draw backs seen in EAP to using the 0331 head?

[1bolt]

How did the 0331 head fair with an aftermarket header for the earlier head and the new manifold vs. the same but with a 0630 head? Besides the cracking in the earlier 0331 heads, are there any draw backs seen in EAP to using the 0331 head?

Well I didn't run that permutation, but I would expect that a longer tube aftermarket header (the long tube Borla averages something like 26 or 28 inches from memory), to improve hp (peak) and maybe bump mid range torque while giving up a little off idle torque (wheel chirping torque I like to think of it)... One problem about using EAP for Jeeps is it doesn't do the best job of predicting below 2000 RPM's because it does not model bogging, swirl/tumble (fuel vaporization effects) etc. which play a large role in how well an engine makes torque at low speeds (but which make no real difference higher in the RPM's).

Besides cracking I don't see any draw backs to using the 0331, but cracking is a biggie. It does seem that past 2001 those heads no longer crack. There's no detrimental effect to having an exhaust port that flows a little less, when it creates much more velocity and thus does a better job of scavenging... Gear heads get worried when they hear the exhausts are smaller; but for any street use (and especially for JEEPS and off-road) smaller exhausts with longer primaries are a very good deal... It's also IMO the best head to start porting on... the exhaust on the earlier ones can't be raised without making it even more lazy at the floor. That port starts out too big and porting it just makes it worse. The 0331 exhaust could be raised probably a 1/4 inch and it would still be smaller than the old overly large ones (IMO).

Man I wish I had more time this makes me want to do some porting, I've started a "max effort" experiment on an 0331 to see how much CFM I can squeeze out with an eye to feeding the new re-worked port volumes and CFM flows to EAP and simulate the results. but I've got a new kid on the way so time is hard to make, and progress is slow. I'm a frustrated David Vizard wannabe

[TheDarkSideofWill]

Subscribing.

[dwg86]

That all makes sense. I would love to see the port shape with an old head cut in half. So running an aftermarket cam with the 0331 head, you sould have a longer exhaust duration as well as bigger lift, due to the exhuast port?

I am planning my next stroker,although that might be a while, as I also have a new Jeeper due to arrive mid December. WOW! a Dad again at 42 years old. Carson Joshua or CJ for short...yes I'm a Jeep nut.

Sorry, I got off track. My next stroker will be built from my 2003 TJ engine, 0331 head. This one will be a long rod engine. I am thinking about another Engle cam, but don't know if I need to go longer on the exhaust duration/lift. I am running an Engle [email protected]/.501 lift on intake and exhaust, 112 lobe centers in my current stroker. I like the cam. I've had it up to 5200 rpm before I left off the gas. I have heard of some and read on Hesco's forum about other cams(didn't say which one) that would only run to about 4200 rpm and then the engine would just stop pulling. Here is a link. 7th post down. http://hescosc.com/forum/forum_posts.as ... PN=1&TPN=1

So I am happy with the Engle cam, but don't know about the exhaust side of the grind for use on an 0331 head. I had thought about having Engle grind a different cam using. [email protected]/.489 lift on the intake, and [email protected]/.501 lift on the exhaust with a 110 lobe seperation, 4.0 rod, 9.5:1 zero deck, Fel Pro MLS head gasket(.039 quench).