Head swap/upgrades

[TheManch]

first off let me say that i have searched and thats why i did some of the things that i did, whether or not some of you know it, i have gotten lots of help from people on here, and i am very much appreciative of that!!! Now onto my questions......

i have a 2000 xj with a FM super 44, bored throttle body, intake, and the dreaded 0331 head. although its a 2000, it does not have the pre-cats or 4 oxygen sensors, it does however have the nicest factory exhaust manifold i have ever seen! and at 67,000 miles it has yet to crack, and neither has my head. Being that i have two 3000 plus mile road trips coming up in the next year, and i'd rather not be stranded somewhere with a cracked head, i got a nice replacement 7120 head for basically nothing and decided that would be my starting point. i took it to what i heard was a local reputable machine shop, and despite what i asked him to do, he did more, went over budget and took too long. thats a different story in itself though. Anyway my head it now very clean and has had the following done to it.

-magnaflux and thorough cleaning
-new K-line bronze guide liners
-3 angle valve job
-machine intake valve bowl and radius combustion chamber,
-back cut intake valves
-surface combustion chamber side of head (about .012)
-surface intake and exhaust side of cyl head.

tomorrow it will be assembled with new mopar valve springs and then i will be picking it up.
based on what i have read on here i can expect to bolt on this head, with the exception of the studs for my coil on plug ingnition setup but i can work around that. because i don't have the pre-cats i should be able to bolt my stock exhaust manifold on for now.

-would there be any gain to me running a thinner head gasket (mopar) and upping my compression ratio? is there anything else that needs to be done along with this.
-how much could i expect to gain by taking apart the head (which i've done before) and cleaning up the intake ports and combustion chambers, as done by many others, of course i would follow what others have done and had work for them, and dino's website has been most helpful with.
-when i swap this head can i use my rockers and pushrods from my 2000? or shout i use the rockers and pushrods from the engine that the head came off of?

thanks for your help guys im still new to anything more than bolt on's for the 4.0, im trying to learn, and what was going to be a simple head refreshing turned into "well as long as im in there............"


mike

 

[5-90]

I didn't want to quote that monster, so let me know if I miss anything (it's easier, if asking a bunch of questions in a post, to number them. Makes it easier to sort the answers, and to make sure they all get answered...)

Thinner head gasket - This is usually done to fine-tune head shaving and things like that, when you're seeking a specific level of "quench." What's quench? Simply put, it's the clearance between the deck line of the piston and the cylinder head (have you gotten my book? I explain it in greater detail in there.) Why is it important? Setting your quench clearance properly (typically .045-.060") forces an eversion of the fuel/air charge, encouraging compleat combustion of the charge and effectively cooling the combustion chamber - this both uses fuel more efficiently and reduces the octane number requirement (ONR) of your fuel - it's why some engines can be built up around 9.7-10.0:1 and still drink 89 octane fuel without trouble. The AMC six is already "quench compliant" - losing .012" from the cylinder head already raises compression slightly (by reducing the combustion chamber,) but a thinner head gasket should not be needed. If you'd decked the short block, I'd say go with a thicker head gasket - or if you change the connecting rods or piston compression height, you'll want to change the head gasket. But, you're not changing the reciprocating assembly, are you?

Head Port Cleanup - I've not seen a lot of before/after comparos on port jobs - it's an angle of research I want to get into. Bear in mind that the same cylinder head, in the same condition, on the same damn day can show different flow results if run on a different bench or a different tech. Therefore, having the "before" done at one shop and the "after" at another is tangentially useful at best - try to get them done by the same guy on the same bench (you can't do anything about barometric pressure changes, so note it when you take your results if it's not on the report already.) Part of what I'm doing is trying to collect one or two of each head for experiments in this very line of research.

Valvetrain Parts - Keep the rockers and pivots together as a set, and you should be fine either way. If I were going to all this trouble, I'd replace them all outright - but that's just me. There's no real harm in reusing them, as long as you don't mix them up (keep the pivots and rockers paired. The bridges and screws don't move in relation to anything, so they're not critical - but you don't really want to mix up pivots and rockers. Some have and not had anything go wrong, some have and ended up tearing them out and replacing them a few weeks later. Why take the chance?)

If you don't need that 0331 head for anything, and you have access to a shop to chop it up for you, I'd like to talk to you about it. I figure, with what I've been able to find out, that it's probably easiest to cut into sections of two cylinders each (through the screw holes) and mail it to me that way using "flat rate" boxes - all I ask is that you mark which cylinders are which (a Sharpie pen will do.) I'd end up cutting the head into cylinders anyhow, and sectioning at least one cylinder into small slices to analyse the casting, so cutting it up isn't a problem.

You may have trouble getting the later exhaust manifold on the earlier head - in order to help reduce emissions ("improving catalyst light-off",) the exhaust ports were reduced on the 0630 and 0331 head, and the 7120 ports are probably too large for the 2K exhaust. See if you can use the manifold that goes with the 710 head, or see about an adapter plate (I may have the thread bookmarked here somewhere - someone was doing a kit for an "0331 to 0630 head conversion" and had sorted it all out before.)

 

[TheManch]

5-90, you're one of those people who have helped me a lot, and im slowly learning more and more from your posts, you book sounds like a something i might have to pick up. here we go and laid out better this time.

1. head gasket: i understand what you are saying about quench and am learning more about its affects. I am not changing the rotating assembly, so i guess for the sake of simplicity i will just use a stock thickness gasket, it was my understanding that if i used a thinner one i could up the compression ratio but i dont want to mess any more with my already quench compliant engine.

2. head port cleanup: well i asked this guy what he thought of me opening up the intake ports and blending them, along with polishing up the ports on the intake side, and removing the tear drop shape around the the valve guide holes. this guy seemed to think that anything i would gain from doing that myself without a flow bench would be negligable, so i took his word for it. i guess in the interest of time, i'll just leave it as he gave it to me.

3.valvetrain parts: when the time comes i will probably just use the stuff thats on my 2000, keeping everything together of course.

4.exhaust: as i understand it you're saying that the exhaust ports are smaller on the head than the exhaust manifold. maybe i could buy a header for 7120 head (say 94 xj) and adapt it to work with the rest of my exhaust, my header is a 6-3-2 design if i remember correctly, so i'd have to have a custom down pipe built.

oh and you have PM 5-90


Mike

 

[gradon]

He was saying that the 7120 head has larger exhaust ports than the 0331 head and so the 0331 exhaust manifold might be too small for the 7120 exhaust ports and might require an adapter plate of sorts or else the use of a 7120/0630 manifold(stock or aftermarket).

 

[5-90]

1) By having the head deck milled/ground, you've already slightly increased the compression ratio. But, you haven't changed the quench clearance (the head deckline is still going to be in the same place relative to the short block,) so go ahead and use the stock gasket.

2) Without a flowbench, it is difficult to see just how much you are gaining by your work, and it's easy to shoot yourself in the foot. However, a simple cleanup job (without changing the shape of the port) won't do any harm - just smooth out the inside radii, clean up the sand-cast surface, and remove any casting flash. "Teardrop-shaping" the valve guides is a good idea, but should be done on a 'bench - that's an easy spot to screw up. If this were a carburetted engine, I'd say don't even smooth out the surface - but the manifold and airflow areas are "dry" (no fuel,) so laminar airflow is more useful than the boundary turbulence used to prevent fuel puddling.

3) Best bet for using old stuff? Keep stuff together. If the stuff off of the 7120 is still in good shape, use that. I don't recall a change in valve sizes over the years, but why take chances? Definitely don't mix up valves once you lap them to a particular seat!

4) As gradon said, the ports in the head are larger than the ports in the manifold. This could result in part of a port being "uncovered" - and you could suck cold air in to the port and warp a valve. Oops. Even maximum-effort engines still have individual header pipes - and do for a reason! The adapter plate is to mate the small manifold ports to the larger head ports - better still, just use the manifold that is sized for the head (if doable) and have done with it.

And, I should have answered your PM by now.

 

[Talyn]

He was saying that the 7120 head has larger exhaust ports than the 0331 head and so the 0331 exhaust manifold might be too small for the 7120 exhaust ports and might require an adapter plate of sorts or else the use of a 7120/0630 manifold(stock or aftermarket).

I didn't like the alignment of the exhaust 00+ manifold with the 7120/0630 head exhaust ports.

 

[TheManch]

Well it looks like i will be getting a header then, i was very happy with my apn on my zj, its till holding strong after 2.5 years. so i will be looking at one of those, i wonder if i can get a replacement header that will go 6 into 2 like mine does so i do not have to get a replacement down tube made. As i understand it i will need a header that bolts to the 7120 head but has the later design of the exhaust. For some reason i remember the 1998's having the 7120/0630 head but having the later exhaust setup, can anyone confirm this?


mike

 

[5-90]

Well it looks like i will be getting a header then, i was very happy with my apn on my zj, its till holding strong after 2.5 years. so i will be looking at one of those, i wonder if i can get a replacement header that will go 6 into 2 like mine does so i do not have to get a replacement down tube made. As i understand it i will need a header that bolts to the 7120 head but has the later design of the exhaust. For some reason i remember the 1998's having the 7120/0630 head but having the later exhaust setup, can anyone confirm this?


mike

1987-1990 #2686
1991-1995 #7120
1996-1998 #0630 (ZJ/YJ/TJ)
1996-1999 #0630 (XJ)
1999-2007 #0331 (WJ/WK/TJ/JK)
2000-2001 #0331 (XJ)

The #0331 head can be readily identified, of course, by the COP/DIS setup, or by the presence of drilled/tapped bosses for mounting the coil rail if the head is bare.

 

[Talyn]

I've done this same swap on my 2000, so if there is an item you are unclear about feel free to ask.

Oh.. and I wanted to add that you will probably be cutting off the Y pipe off the stock intake manifolds to fit your after market header in. Also, I have heard that the aftermarket headers for the 0331 heads will work on the earlier heads with no problems as they are larger... I can't confirm that but i have heard that. BTW, where is your upstream O2 sensor (the one closer to the engine)?

 

[TheManch]

Y pipe: what y pipe are you speaking of on the intake manifold, some sort of a exhaust gas recirc. setup? i can't run out an look right now but i will try to later.

O2 Sensor: my upstream o2 sensor is on the down pipe near the transmission/engine junction.

Header: i will try to find a reasonably priced header for my setup, i would like to run a later model header, that way i wouldn't have to mess with my down pipe setup. APN doesn't have a header for my year, i actually called asked for one that has the dual outlet like mine does and he said that they don't have one like that. Which header did you end up using Talyn? Maybe my best option, though no the cheapest would be to get an APN header and then have a custom down pipe made.

 

[seanyb505]

Im guessing based on the prices of most headers and the inexpensiveness of the APN, that the APN and custom downpipe might be cheaper than other headers. Maybe 225 tops for both?

 

[Talyn]

APN is a decent quality header. I have only heard of one cracking. However, I haven't heard of a single header for the 4.0L that won't crack. The only good thing about the more expensive after market headers is that some carry a life time warranty.

 

[Talyn]

Y pipe: what y pipe are you speaking of on the intake manifold, some sort of a exhaust gas recirc. setup? i can't run out an look right now but i will try to later.

The Y pipe is the pipe immediately off your two piece stock exhaust manifold.

I am using a Doug Thorley header. There is a company called IIRC Rocky Ridge that makes a late model style header.

 

[TheManch]

Im thinking i might end up with an APN and a custom 2.5 down tube with a the bung for the 02 sensor. Of course it will be the older style with out the Y style collector.

Im sorry Talyn i thought you said intake manifold in your first post, but it makes more sense now that you said exhaust manifold.

On a side not how do you like your doug thorley, im looking at a banks header locally, or he said it was a banks its off of a 97 xj engine, it looks exactly like my APN did, just way dirtier haha.


Mike

 

[Talyn]

On a side not how do you like your doug thorley, im looking at a banks header locally, or he said it was a banks its off of a 97 xj engine, it looks exactly like my APN did, just way dirtier haha.


Having a life time warranty is nice. I used it 3 times. Nice design, good materials, but I have had issues with the coating flaking off.

 

[gradon]

Nice sig Talyn--How long before you get tired of thinking about PC every time you post before you change it?

 

[Talyn]

Until it stops making me laugh.