7120 Head worth putting on over 0630?

I Removed the Head on my 98 Cherokee with the 0630 head. I have a 7120 head Both of them need a Valve job. Is the 7120 worth bolting onto my motor is there really a difference??? I know my manifold and intake should bolt right up?? but what are people doing about the 7120 not being machined for the Dowl pins the later blocks have?

I believe the 7120 is only popular because it's more receptive to porting.

So if you plan on porting it's worth it.

thanks for your quick response. i only plan to have a valve job done and have it magnefluxed and checked over.

As always this page from Dr. Dyno is worth the read.

http://www.jeep4.0performance.4mg.com/head.html

good info on that site...they state 7120 being better flowing over the 630...but does not state how much?

I haven't done side-by-side "apples to apples" comparos on this yet, I'm still collecting heads.

However, anecdotal evidence supports the 7120 as being a more "breathable" head than the rest, even without porting or extensive valve work. The catch? For you, it's the exhaust ports. The exhaust ports were reduced in size on the 0630 to "improve catalyst light-off times" (keeping the volume for the exhaust pulses to move through smaller means they retain more heat. It's an emissions move, more than anything else,) so you'll either need to adapt the ports down to the later manifold - you can use an adapter plate to do that, and it's been covered here before - or you'll need to use the earlier (1991-1995) OEM header, OR you'll use an aftermarket header to obviate the entire problem. The 7120 exhaust ports are slightly larger than the 0630 primary openings, and you can end up with exhaust leaks that way.

the aftermarket header i bought said it fit 91-99 cherokees...so i should be good there...looks like i will have the valve job done on the 7120 vs the 630....i also will be installing my 99+ intake manifold....so hopefully with new lifter...(old ones were just plain worn out) and a nice tight head this thing will be a beast.

It wont be a beast, trust me.

I re-did a 7120 head and took off my 0630 when it cracked. I got a valve job, took off .035" off the head, and even put in a .041" head gasket (mopar performance) and it's worth bragging about.

I'm also running 35's and the ax-15. Not enough power for my own personal taste... so I'm dropping in an LS1.

Going to teh 7120 head will net you some improvement - but it won't be "beastly," as previously mentioned.

If you want to do something "beastly," get yourself a 258ci crank and rods, bore the block +.060", then slap that head on there - now you're working on a beast! Throw on 24-25#/hr LT1 or SBFord 4-hole injectors (higher delivery rate, finer fuel atomisation,) and consider setting up a MAP adjuster to fine-tune your fuel delivery.

Hell, even just throwing a 258ci crank and rods in with the 242ci slugs under that 7120 head and 1999-up intake should be a significant improvement. If throttle response is important to you, throw on a SBFord MPI throttle body (like out of a 5.0 Mustang) and you'll get better part-throttle response. It's not a "performance adder" in its own right, but it will feel like one. The OEM throttle body flows well enough to supply air for the stroker.

selarep said:

It wont be a beast, trust me.

I re-did a 7120 head and took off my 0630 when it cracked. I got a valve job, took off .035" off the head, and even put in a .041" head gasket (mopar performance) and it's worth bragging about.

I'm also running 35's and the ax-15. Not enough power for my own personal taste... so I'm dropping in an LS1.

Click to expand...

You had an 0630 that cracked? I haven't heard of those cracking before! Only 0331 heads.....

Blaine B. said:

You had an 0630 that cracked? I haven't heard of those cracking before! Only 0331 heads.....

Click to expand...

No - I've got an 0630 that I picked up with some extensive chamber cracking in #1 and #2, with some more in #3 (all cracks seem to originate from the valve seats so far...)

@selarep - next time we can manage to link up, I'd still like to get that cracked 0630 from you - if you haven't already disposed of it.

Mine cracked off at the thermo housing. It was not worth repairing so I built up a 7120.

Jon: let me know, I still have it, I think...