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0630 vs 0331

Root Moose

NAXJA Forum User
Location
ON, Canada
Is there any real difference between these head castings other than the provisions for the DIS on the 0331?

Different chamber size? Valve size? Other things?
 
HO head #7120 & #0630

Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 66.0 128.0 179.0 206.0 209.0 209.0
Exhaust flow. 55.0 100.0 120.0 136.0 141.0 141.2

HO head #0331

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 114.0 165.0 194.0 199.0 205.0
Exhaust flow....94.0 117.0 126.0 130.0 133.0

Ported big valve 2.02/1.60 HO head

Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5
Intake flow.... 73.9 142.4 197.8 229.8 247.0
Exhaust flow. 65.3 114.0 135.9 146.3 157.1

The early '87-'90 non-HO heads have low intake ports that flow rather poorly. The later HO heads have higher intake ports that flow more air by allowing a straighter shot into the cylinders. The '91-'95 HO heads with casting no.7120 have the highest intake and exhaust port airflows, especially at lower valve lifts where it is most important, and are the best for performance. The '96-'98 0630 heads are almost identical except that they don't have a port for the coolant temp. gauge sending unit. The '99 and later HO heads with casting no.0331 have smaller exhaust ports to produce a faster warm-up of the catalytic converter and improve emissions, but performance also suffers because the ports don't flow as well as those of the 7120 and 0630 castings.
The exhaust ports flow relatively poorly compared to the intake ports on all the 4.0 heads so this engine would perform better with a dual pattern cam that has more exhaust valve opening duration and lift than the intake. Jeep recognised this and increased the exhaust valve opening duration on the '99 and later cam to compensate for the poorer exhaust port flow of the 0331 head.
 
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So can anyone provide any guidance as to whether an originally 0331 equipped engine retrofitted with a 0630 head would have issues passing emmisions?

Is the difference signifigant or would a otherwise healthy engine pass the 2001 emmisions standards even with the "dirtier" 0630 head?


I'm not needing a head swap yet... but if it comes to pass I'll try to squeak past emmisions with the 0630 head.

(we don't have visual of that "depth" - cat installed? yes, continue)
 
The 0630 is a better stock head. It flows better as stated above and doesn't crack as easily as the 0331. The only issue would be fabbing up some brackets to hold your igntion rail. (I'm assuming you have distributorless ignition.)

I don't think you would have any problems passing emissions with a 0630. Just make sure your engine looks clean the day of your test. You wouldn't impress a date wearing a dirty t shirt and torn jeans, and you won't impress the emissions tech with a soiled and oily engine. So get some engine degreaser after your head swap.

Another thing, if your going to the trouble of swapping heads, take this opportunity to give the 0630 head a good port/valve job. You will gain significant high rpm power if you do this correctly.

 
Avoid the 0331 heads like the plague. Apart from the fact that the exhaust ports are tiny, these heads are crack prone especially between the 60,000-90,000 mile mark (outside the powertrain warranty period so basically you're screwed if it happens).
 
Buy one of the aluminum replacement heads!!!

Then tell us mere mortals how it works and show us how you did the swap!

That's what I'd have Over-Haulin' do to my XJ, boy!
 
Dr. Dyno said:
On yeah, those heads are a bargain; Summit Racing sell them for $1400 bare and $1500 assembled, while Hesco sell them for $1850.

$1850 per head? Definetely a bargain!
I think I'll buy two of them, I'll keep the second one in my living room for decoration purposes :)
BTW a friend of mine bought a pair for the V8 of his Mustang. After he put them on compression and performance evaporated.
It seems that even though they were listed as replacements, he was supposed to know that the chamber volume was not identical to the original, Edelbrock told him to shave a few thousands and use a thinner head gasket.
He even had the block shaved a bit. What a cluster....
 
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Dr. Dyno said:
Avoid the 0331 heads like the plague. Apart from the fact that the exhaust ports are tiny, these heads are crack prone especially between the 60,000-90,000 mile mark (outside the powertrain warranty period so basically you're screwed if it happens).


Actually, I believe there might be a recall on this one. A friend of mine bought a 01 used and with in the frist week of owner ship it started to overheat and go thru coolant like water on her. After some research here, I told her to take it back and they relaced the head free of charge. I am not sure how, shop warrenty or recall, but its definately worth a shot.


Oh yeah, the Dr is right on this one.........besides the low pinion front axle, extra cats........this is the other reason to stay away from the later 99's and newer.....if buying used.
 
CartsXJ said:
Actually, I believe there might be a recall on this one. A friend of mine bought a 01 used and with in the frist week of owner ship it started to overheat and go thru coolant like water on her. After some research here, I told her to take it back and they relaced the head free of charge. I am not sure how, shop warrenty or recall, but its definately worth a shot.

Likely shop recall. There has not been a recall on the 0331 and there likely will not be from what I read. There are two many 0331 castings that work fine.
 
I don't know if you read my other post on swaping the shafts out of the Low P 30 in to a HP 30, but to make a long story short my 92 was totaled by an idiot, and I know have a 01. I bought the 92 back from the Insurance company for 400 bucks. So I have the head on that engine, which I had a tri angle valve job and recessed valves instaled. How hard to swap it over, just the ignition rail Issue? Sounds Like a no brainer as far a quality and performance. Might be worth it just to get rid of that stupid child proof oil cap on the valve cover.
 
I just replaced my 0331 3 weeks ago before my Moab trip. No change im MPG but definately felt more low end torque. Changed out a few other items while I had everything down.

Fabbing up a couple of straps from the ign rail to the valve cover bolts didn't take much, so that wasn't a problem.

To me, it was a worthwhile swap as I was just beginning to notice issues that was pointing to the head. To bad DC didn't have the same foresight.
 
Which head did you use the 7120 or the 0630? Can you post a pick of your retrofit? I am sure I can figure out how to make the straps work, but it never hurts to see someone elses ideas.
 
Rattman said:
Which head did you use the 7120 or the 0630? Can you post a pick of your retrofit? I am sure I can figure out how to make the straps work, but it never hurts to see someone elses ideas.
Yup! I can either post up a pic tonight or in the A.M. sure. Family arriving from TN so depending on time.

When I dropped in the 0630 head, I did it with the intake/exhaust already mounted. A few people advised against it, but since I had a lift and extra muscle, it went down real smoothe. Glad I did it, 'cause getting to those manifold bolts was a PIA that I wasn't looking forward to.
 
rstarch345 said:
Yup! I can either post up a pic tonight or in the A.M. sure. Family arriving from TN so depending on time.

When I dropped in the 0630 head, I did it with the intake/exhaust already mounted. A few people advised against it, but since I had a lift and extra muscle, it went down real smoothe. Glad I did it, 'cause getting to those manifold bolts was a PIA that I wasn't looking forward to.

Don't see why people would advise against it - I tend to advise people to do that, for the same reason you noted! It's a lot easier to service the manifold gasket on the bench than on the engine - by a couple orders of magnitude...

Granted, I'm a fairly large individual, and waving around a two-foot long iron casting isn't that big a deal for me, but if you're going to do the job and you don't have the power to do it yourself, get someone who can help you who can follow instructions immediately and accurately. Two extra hands helps - but they've got to be hooked to a single brain order to work...

5-90
 
5-90 said:
Don't see why people would advise against it - I tend to advise people to do that, for the same reason you noted! It's a lot easier to service the manifold gasket on the bench than on the engine - by a couple orders of magnitude...

Granted, I'm a fairly large individual, and waving around a two-foot long iron casting isn't that big a deal for me, but if you're going to do the job and you don't have the power to do it yourself, get someone who can help you who can follow instructions immediately and accurately. Two extra hands helps - but they've got to be hooked to a single brain order to work...

5-90
I believe the concern was in making sure the head got placed properly w/o messing up the head gasket. Once you add the intake/exhaust manifold, you add about another 30 lbs to an already 80+ lbs and that 30 lbs is off center. It makes handling very nasty even with a lift.

Most professional mechs think the average do-it-yourselfer is brain dead and will just muscle the thing in figuring they'll be the one to correct the idots mistake, and understandably. But I'm one of the old farts that's been doing this stuff for years. Yogi put it best; "I'm smarter than the average bear". That includes knowing when I've reached my limit of ability. Anyway, I took maybe 20 minutes to drop that head down. I constantly adjusted the angle on the lift with my helper adjusting the load. We dropped it perfectly flat. That was one sweet swap over.
 
Yup - I do much the same thing, but I use alignment pins and muscle power (I don't have a cherry-picker.)

Some 1/2" allthread rod comes in quite handy here - screw it in (leaving about 6" or so sticking up over the deck,) line the head up on the rods, and slowly lower. Put most of the screws in finger tight, remove the rods, and replace with screws. Torque to spec.

I haven't gotten around to taking measurements for head studs yet...

5-90
 
The pics would be greatly appreciated, I probably won't get to it untill the weekend so no rush on the pics. I have a plenty of space and all the tools nessicary for fixing a tractor so it should not be a problem. I have rebuilt engines by myself so I know a little bit about what I am doing. Don't get me wrong I am not an expert by any means and probably take twice or three times as longs as good mechanic. They ran like tops when I was done.
 
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Two brackets seem to work well. The only thing I haven't done is to cut the extensions going down to the block. At the time it appeared they had metal inserts in the plastic and I didn't want to fool with them. So I used the origional bolts, tack welded a nut to a piece of 1/2x1 flat stock so I could get the nut on the end of the bolt. It's tight down there. Next time I have to pull the rail off, I'm plan on cutting them down and using shorter bolts.

I used some scrap flat aluminum stock I had as it was easy to form for the fit I wanted.
 
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