4.0 questions!

I have a 97 4.0 xj, i also have a 4.0 block from a 91 or 92 not sure, is there anyway to tell if the 91/92 is a HO? Will the head from the 97 bolt up to the older block? Will i have to change any electronics if those answers are yes? thanx guys! any help related to these parts will help a lot!

All 4.0 engines, from 1991 up, are "High Output" engines. The "HO" designation came into play when ChryCo started fitting their (OBD-compliant) electronics to the block to replace the RENIX (I feel like I've covered this recently...)

The heads are readily swappable, so that should not be an issue. The 242 heads will, in fact, bolt right onto a 258 block, as will the other AMC I6 heads - se heads are swappable between 199-232-242-258 engines, as long as you bring the rest of the top end along for the job.

The principal casting changes made to the block over its production life were to either reduce weight (thinner cylinder walls and webs,) or to reduce NVH (Noise, Vibration, Harshness - some more esoteric mods.) The deck remained virtually unchanged over the production life of the 4.0, from 1987 to 2007 (which, I am informed, will be the last year for the 4.0. Pity - the Small Block Chevvy engine has been around for 50 years with minimal changes...)

You may want to search for my recent posts advising others on this - I've covered this in fair detail recently, and I see no reason to do so again. I'm probably going to end up doing a FAQ writeup for easy reference...

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I've bolted a '95 head to an '03 block. There are some small differences between the blocks. Overall they won't pervent you from swapping blocks. The 87-95 blocks don't have dowel pins to align the heads onto them. The 96+ blocks do. This shouldn't be a problem. You can look down the bolt holes and center the head by them.
Tom

thanx for all the help! i have some more questions, does anybody know the stock exh/int valve size for a stock 4.0L HO? And the stock cylinder bore size?

Stock bore is 3.875", or 3-7/8".

I'm inclined to think the valves are 1.91/1.60, but I'm not sure - hold on while I dig up my book...

Close - 1.90/1.50" is what I have listed in my book, which means I either verified that directly or from several independent sources. I don't much care for guessing...

Anything else?

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yeh i am sure ill have some more questions lol, do you have any experience with what size is reasonable for porting the valves to? I am a chevy man besides my xj so dont know to much but small block chevys lol, is any head work needed for a mild cam install, with reguards to push rods? or for a roller rocker install? thanx a lot, you are really helpin me out!!

I'd think you'd be more interested in just cleaning up the ports, rather than doing a port job. Don't do any major port work unless you have a flowbench...

You'll see some gains with just cleaning up the ports and not actually removing a great deal of material - especially cleaning up the intake ports.

It's theoretically possible to go up to 2.02/1.60" for valves, but I'd not think it's necessary. Since the I6 is generally a low-revving animal, and we're usually more interested in torque than horsepower anyhow, you'll probably see your engine living at about 2000-3500rpm for most of its life.

Roller rockers are likewise - if you're running at high revs, you'll see some utility, but otherwise probably not.

Changing pushrods should not be required unless you're having the head shaved, and you probably don't need to shave the head unless its warped (which isn't really likely.) If you change the cam, tho, DO make sure to use the springs recommended by the manufacturer - spring bind will wreck quite a few things. Ideally, when the lobe is at full lift, you should still have something like .100" total space between coils (with five spaces, for instance, you should have no trouble sticking a .020" feeler gage in each gap. More is usually better.)

Anything else?

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