4.0 HO
- Thread starter mrVfr
- Start date
Bounty__Hunter
Super Moderator
Cherokee's and Commanche's had a fuel injected 4.0L that was non-HO, it's known as the Renix 4.0L engine. Pre '91.
Was '91 the first year for the HO or was it '92?
Was '91 the first year for the HO or was it '92?
LVRockCrawler
New member
had a 4.0 HO in my 91 Sahara
LVRockCrawler
New member
will the 4.0 HO head bolt up to the 258 and still use the stock intake/exhaust?
LV, you can use your factory intake, but it's going to cost you some power. Clifford makes a nice one that allows you to run the wonderful 390cfm Holley four barrel and improves breathing greatly. You will need a 4.0 exhaust manifold or a header made for the 4.0.
The head requires some water jacket mods to work on the 4.2, but any rebuild shop should be able to handle that. I think the head bolts are 1/2" on all 4.0 heads too, but your 89 4.2 should already have them. If not, drilling and tapping the 7/16" holes out to the 1/2" thread is an easy fix too, I also think some stepped bolts or spacers are available if you don't want to drill your block.
It's worth 30-40 horses on the 4.2, and even more with a good camshaft, header, and four barrel intake. Things like roller rockers and a hotter ignition make it work even better. Short of a big bore 4.0 based stroker, this route will give you the most your going to get out of a Jeep I6 without nitrous, supercharging, or a turbo. I'm planning a stroker for the TJ, it's gonna be a V8 eater :twisted:
The head requires some water jacket mods to work on the 4.2, but any rebuild shop should be able to handle that. I think the head bolts are 1/2" on all 4.0 heads too, but your 89 4.2 should already have them. If not, drilling and tapping the 7/16" holes out to the 1/2" thread is an easy fix too, I also think some stepped bolts or spacers are available if you don't want to drill your block.
It's worth 30-40 horses on the 4.2, and even more with a good camshaft, header, and four barrel intake. Things like roller rockers and a hotter ignition make it work even better. Short of a big bore 4.0 based stroker, this route will give you the most your going to get out of a Jeep I6 without nitrous, supercharging, or a turbo. I'm planning a stroker for the TJ, it's gonna be a V8 eater :twisted:
Bounty__Hunter
Super Moderator
You can reuse the factory manifolds, but the intake needs a few modifications as it mounts up higher than on the 4.2L head. A little grinding on the intake and use of large washers to hold the intake to the head is all that's needed. Do a search, there's a ton out there. There's even a whole forum dedicated to this swap, I'll try and find it.LVRockCrawler said:
