4.0 to 4.2 swap, anybody done it?

[Randre]

Anybody ever put a 4.2 into a late model (1998) cherokee?

I have the opportunity to buy a 4.2 out of a 1990 YJ for a couple of large, its got 10K miles, a performance cam, forged pistons bored .30 over, and the blocks been decked. I have read about puting on the late model heads onto the 4.2, but not sure what might be involved with doing that and then dropping the 4.2 into the cherokee.

Areas of concern are mainly

1. drive belts, harmonic balancer and accesorries

2. Distributor and ECU electronics

3. Flywheel and tranny. YJ was a manual, I have a Auto

Any help would be appreciated.

Randy

 

[dennisuello]

why? is this 4.2 FI or carburated?

 

[ZmOz]

4.2 is carbed, but if you put on the 4.0 head it will use the stock fuel injection. I wouldn't do it though....4.0's are cheap and easy to find...

 

[Eagle]

Dunno if you care, but technically in California (as well as some other jurisdictions) this swap is illegal. You can't put an engine from an earlier year into a later vehicle that the engine was never offered in.

Reality check -- the two blocks are virtually identical externally, so it's unlikely (but not impossible) that the smog ref would catch the swap.

If the 4.2L is set up with a serpentine belt you're safe regarding belts. If it has multiple vee belts, the crank snout is probably too long by a fraction of an inch.

If you swap on the head from a '99 4.0L, you can use the injection and all electronics along with it. The 4.2L won't have a flywheel that's set up to run your CPS, so you'll need a '99 flywheel or flex plate. You may also need to fab a couple of bracket mounts, but most of what you need should come in with the manifolds and late model head.

 

[Randre]

Thanks.

I have a 98 XJ, so what I'm looking to do is swap the block to get the longer stroke and the benefits of the performance mods already on this particular 4.2

Anybody know if the 90 TJ had v-belts or serpentine?

Not worried about smog issues, don't live in a Socialist State.

Flywheel should be no problem as long as I can swap with mine from the 98.

Thanks

Randy

 

[ZmOz]

So you don't consider california to be a socialist state? :laugh2: :laugh2:

 

[Randre]

I don't live full time nor register my vehicle in California, I'm just here on a contract basis. But to answer your question, yes California is the Mother of all Socialist States. I can't wait to go home !

 

[Ed A. Stevens]

IIRC, all YJ's used a serpentine belt drive for the water pump, and should have the correct balancer snout depth (all the CA YJ's did).

The 4.2 makes a great low effort alternative to a stroker. Just strip the head, the flywheel, and all the accessories from the XJ engine and put them on the 4.2 block. If it's a 90' 4.2 it should have the wide deck and not expose the 4.0L head water jacket ports.

You need to check and use the correct rotation pump (use the XJ water pump and accesories).

Identify the cam in the 4.2. If it's a stock 4.2 cam the 4.0L is likely to be a better choice. If it's an aftermarket cam make sure the valve springs can take the lift height (Mopar has drop-in springs from a 5.2 or 5.6, a 318 or 360, V8.) Index the cam timing, as the 4.2 and later 4.0L cams have been found to be keyed as much as 6 degrees retarded (rumored to be for emissions reasons, but is probably production variation).

The 4.2L head is more restrictive than your 99 4.0L, don't waste any effort on the 4.2 head. If you want slightly more power find a 91-96 4.0L head (Dino has the casting numbers compiled from the Strokers group on his web pages).

The carb choices all pale compared to the XJ MPI system, even the 500cfm downdraft Weber 38/38 and 390 cfm Holly 4-barrel on Clifford intakes. Your 99' intake is assumed to be the better 4.0L intake, due to the more equal length runners that better define the torque peak rpm (it benefits from placing the torque peak of all cylinders closer together).

I have a good friend with a 258, with a 93 HO head and Mopar MPI kit (94 HO MPI), that we modified and installed in his CJ. It runs excellent and passes all emissions testing. It's a good second alternative to a stroker, with less machine work.

Let us know what you end up with?

 

[Z22_Z33]

whats the power of a 4.2 how is it better then a 4.0? how much cheaper is it then a stroker?

 

[ZmOz]

whats the power of a 4.2 how is it better then a 4.0? how much cheaper is it then a stroker?

A stock 4.2 is significantly less than a 4.0. If you use a 4.0 head and FI, it's probably about the same HP - maybe a couple more.

 

[Dr. Dyno]

Anybody ever put a 4.2 into a late model (1998) cherokee?

I have the opportunity to buy a 4.2 out of a 1990 YJ for a couple of large, its got 10K miles, a performance cam, forged pistons bored .30 over, and the blocks been decked. I have read about puting on the late model heads onto the 4.2, but not sure what might be involved with doing that and then dropping the 4.2 into the cherokee.

Areas of concern are mainly

1. drive belts, harmonic balancer and accesorries

2. Distributor and ECU electronics

3. Flywheel and tranny. YJ was a manual, I have a Auto

Any help would be appreciated.

Randy

Here's what I suggest you do:

1. Use the 4.2 short block including the performance cam that comes with it.
2. Use crank pulley, water pump, flywheel, distributor, manifolds, EFI, wiring, and computer from the 4.0.
3. Use your existing 4.0 head but do a Dino-style home port job on it.
4. Use valve springs, retainers, and locks that came with the 4.2 performance cam.
5. You'll need to get a pilot bearing for the '90 4.2 crank.

 

[Eagle]

A stock 4.2 is significantly less than a 4.0. If you use a 4.0 head and FI, it's probably about the same HP - maybe a couple more.

That's because the 4.2 was never offered stock with multi-port fuel injection. The advantage over a 4.0L is a few more cubic inches, but a longer stroke, which yields more torque. Anything that produces more torque is better for off-road use.