bubbarules1958

Will a 90 renix engine directly bolt and wire into my 91?

NewKindOfClown

Nope. The electrical was changed in '91. It can be done, but it isn't as easy as plugging everything in.

bubbarules1958

Just swap intakes?

DFlintstone

Check out Cruisers "HO to Renix" swap in my (or his) signature. Since you are doing the opposite I'd guess that should be helpful. You are gonna keep the 91 torque plate for sure, and the manifolds, I'm pretty sure. (so your 91 sensors plug into the harness). You need to use the right manifold gasket, I don't know which, but ..one works IIRC. If Cruiser doesn't show up today, he will likely find you early in the AM.

OK, I took a look, the 91 dizzy also, and my guess, a 91 gasket. I'm sure you will need your 91 CPS as well.

cruiser54

Frickin easy and only pooh-poohed by those with no knowledge on the subject.
Use your flexplate/flywheel. Your distributor, intake and exhaust manifolds with the 91 intake/exhaust gasket. Any questions, post them up.

bubbarules1958

So my HO intake will work on the renix? And the distributor do I need set the top dead center on plug one bull****?

cruiser54

Yes. Use the HO gasket.



Setting Your 4.0 at #1 TDC
　
With #1 spark plug removed, turn the engine over clockwise using the 3/4" front crankshaft bolt. You will see the degree marks on your front cover. Mark the 0 with chalk or white-out.You will see the timing mark on the balancer. Mark it with chalk or white-out. While turning the engine over, put your finger/thumb over #1 spark plug hole. As the mark on the balancer approaches the marks on the front cover, if you are coming up on #1 TDC, pressure in the cylinder will push on your finger. If there's no pressure, you're at #6 TDC and need to crank the engine over until you see the marks coming together and you get pressure. Set the mark on the balancer to the 0 mark on the front cover.

http://www.angelfire.com/my/fan/dist_index.html

DFlintstone

Do be aware that the diagrams you will find are wrong. #1 on the dizzy is at 5:00 as viewed from the side.

bubbarules1958

Awesome guys. Thank you for all of your professional advice. As I get into the swap this weekend I will be sure to post more questions if needed.

bubbarules1958

Not the gasket. The HO intake manifold itself. I was told by somebody else that the HO intake manifold wont work on the renix engine.

DFlintstone

I'd trust Cruiser. DO use the HO manifold gasket. I believe it has to do with the height of the intake ports. I've never even pulled a head off a 4.0 myself!

Anyway here is some "trivia" > http://www.jeep4.0performance.4mg.com/tech_specs.html
"The early '87-'90 non-HO heads have low intake ports that flow rather poorly. The later HO heads have higher intake ports that flow more air by allowing a straighter shot into the cylinders"

cruiser54

Use the gasket to match your intake manifold, whichever you are using.

bubbarules1958

Is the HO head compatiable with the renix engine? Would swapping the head be worth my time? Power gains or anything like that?

cruiser54

It will bolt right on and work. I wouldn't bother.

First off, the HO is not magic. It was basically a way for the Chrysler engineers to toot their horn because they supposedly improved AMC's engine. and what a marketing ploy it was.

The HO only had 8 more horsepower than th 89 and 90 Renix 4.0s.
The HO had a better header than the Renix, a 58mm throttle body versus the Renix 52mm one. Same cam.
The torque was the same and the 8 horsepower were only at the higher RPMs, probably due to the bigger throttle body and better header. Don't give the HO head too much credit for the horsepower gain.

You can get a bolt-on 60mm throtle body for a Renix for under $100.....

DFlintstone

If I had the opportunity, I might do a wet/dry compression test on both of them. Numbers that don't come up wet indicate valves not seating well. My 90 seems to be fine with nutty high miles though. (276K)