Nice find!
Here is a quote from the same forum^: It's based on the idea behind the design of the 0331 head.
"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)."
IMO The 0331 is not a bad head, especially if it has the stock block(stock stroke and bore). The cracking issue can be fixed or prevented by simply maintaining the cooling system and not letting the jeep run too hot or by simply buying an Alabama cylinder head or a TUPY 0331 cast.
and google. Like I've said before, further down the road, I'll take a preventative measure and change the head for a thicker cast version. At that time, I'll take advantage and get a used TUPY 0331 head get it cleaned, magnafluxed, 3 angle valve job and the valve guide bosses grinded down a bit along with the injector bosses of the intake manifold. I might just get it decked .010 and use the thinner version mopar head gasket or just get the thinner head gasket. I would like to keep using 87 octane gas without it pinging.
