4.0 or 4.2 Cam?

[guy'sxj]

I recently joined the submarine club in my '89 XJ and wasted the 4.0. I was given a 4.2 out of a carb'ed '89 YJ. It looks as if the 4.0 head, manifolds, water pump and harmonic balancer will fit it. I'm going to keep the F.I. and renix systems.
My concern is the cam, I saw the cam specs. at Dino's site and they don't even look close to being the same. I don't have the funds nor the time right now so new/ aftermarket is out of the question for now.
This is a trails only rig.
Does anyone know which of the two cams would be best to use?

TIA
Guy

 

[Ed A. Stevens]

Use the 4.0L cam.

IIRC, the 89 YJ 4.2L cam is the same, but if the 4.0L cam is good why change (and create potential problems)?

Are you replacing the lifters (recommended), or trying to reuse the old ones?

 

[MudDawg]

If you do reuse the lifters...be dern sure they go back in exactly the same holes or you will be pulling the cam out and replacing it. otherwise use new lifters with plenty of cam lube.

 

[guy'sxj]

I defintely don't want to create problems. I was going to use the 4.2 short block and cam and use the 4.0 head and manifolds until I saw the cam specs. here http://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm. Now I'm not too sure the 4.2 cam will work well.
Looking at the numbers IIRC the 4.2 cam might give me more low end torque, if it does thats fine but I'm not too certain that it'll work with the renix system.


Guy

 

[Eagle]

The 4.2L was built as a torque engine. Chrysler sells a kit to convert the carbureted 4.2Ls to EFI, and they do NOT give you a new cam with the kit. I would run the 4.2L cam, leave the 4.2L lifter in the holes, and slap on the 4.0L head.

 

[guy'sxj]

Thanks for the answers. Now the next question, if using the 4.2 cam what push rods do I use the 4.0's are 9 5/8" and the 4.2's are 9 3/4"?

Guy

 

[5-90]

The 4.0. The difference in the pushrods has to do with deck height - not with the camshaft.

5-90