4.0 High output

I was just wondering what the difference was between the 4.0 and the 4.0 High Output engines? Is it something I should pay attention to when buying replacement parts? I have a 92 Limited w/4.0 HO.

thanks,
chris

The "High Output" 4.0L isn't that much higher than the RENIX, and the main differences are that the intake ports in the head were raised about 5/8", and the fact that it's a ChryCo OBD control setup instead of the RENIX pre-OBD.

Breaks to watch out for are mainly in the cylinder heads, and are as follows:

1987-1990 (#2685) The RENIX years. Pre-OBD, had EGR valve.
1991-1995 (#7120) OBD-I with Chrysler controls. EGR Valve Deleted
1996-1999(TJ/WJ)/2000(XJ) (#0630) OBD-II with ChryCo controls. Exhaust ports reduced in size slightly.
2000/2001-2007 (#0331) OBD-II with ChryCo controls and Distributorless Ignition System. Reduced exhaust ports to improve catalyst light-off times. N.B. this is the casting that has been known to crack at the centre!

The OBD versions of the engine (1991-2007) have more performance-oriented options available, especially if you live in CA. If you don't, and aren't subject to other branches of the Air Police, you've got more options - but you should already have the #7120 cylinder head, which is usually regarded as the "best-breathing" of the cylinder heads. You can put a later intake on the earlier head (which flows better,) and pick up a few more ponies that way.

You should watch out a bit when buying replacement parts, but unless you're dealing with the manifolds, pretty much everything will fit everything else (AMC was nice like that. Hell, you could drop a crankshaft from a first-year 199ci I6 into your late 242 and "destroke" the engine if you like. It's possible, and would be quite easy to do.)

The principal changes to the engine block where revisions of the casting alloy (nickel content was reduced starting around 1991) and lightening of the casting for NVH reasons. The cylinder heads were revised as above. However, any 242 head will bolt onto any 242 block - and you can even get away with the swaps going onto 258ci blocks back to about 1975 or so. (Bolting a 242 head onto a 258 block and carrying the fuel injection along is a fairly common performance swap for the CJ crowd.)

If you still have more specific questions, don't be afraid to ask! It's just that when you ask a widely open-ended question like this, don't expect a specific answer. I can't read your mind and find out what you're thinking. I'm perfectly willing to help (just like about everyone else here...) but if you want a specific answer, you'll need to ask a specific question.

Welcome aboard!

thanks, i just wanted to make sure i didn't put on the wrong water pump or cap and rotor or plugs, etc. i've never specified that it was an HO when i purchased parts.

Basically 91-up are HO even though they dropped calling it the HO in later years.

tahoe91xj said:

thanks, i just wanted to make sure i didn't put on the wrong water pump or cap and rotor or plugs, etc. i've never specified that it was an HO when i purchased parts.

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Nah - it was a marketing gimmick. All 4.0L engine from 1991 forward are "High Output," earlier ones are not. And, they used pretty much the same block anyhow - the differences were in the cylinder heads and the engine controls.

have a 94 grd.chero. limited, 4.0ho,lots of miles. looking to buy a 2001 with 4.0, chero sport with 87,000 miles.one reply i read was the intakes might crack. anyone have any inputs on this subject ? thanks. new to this site,so don't be to hard on me,hahaha.

splitshotka@yahoo. said:

have a 94 grd.chero. limited, 4.0ho,lots of miles. looking to buy a 2001 with 4.0, chero sport with 87,000 miles.one reply i read was the intakes might crack. anyone have any inputs on this subject ? thanks. new to this site,so don't be to hard on me,hahaha.

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Only if when they are put back on the alignment dowel isn't lined up.