[90yjkrawler]

I know that people have told me not to get a non H.O. 4.0L that was older than 1991. I just don't know why. So I bought a 91 4.0L but I've come across an 89 I think it is. I need to know what the difference is before I get it. I'm thinking of using it as a backup!

[Brandon_YJ]

I believe, and don't quote me on this, that the major difference is that the head on the HO flows much MUCH better.
I mean, I know the head is all that and a bag of chips on an HO as compared to a non-HO, but I'm not sure what other changes were made to the engine.

[rustywrangler]

Read the Renix info in the XJ FAQ section. It is a completely different head, fuel setup.

[Cross]

I did not look for anything older than a 91 due to the fuel injection. There was no way I was going to deal with having a carb. Not to mention off roading the fuel injection performs a lot better.

[sprowley]

craptastic fuel injection, if I'm remembering correctly. 90 and back have a ****ty Ren/ix TBI system and 91 and forward have a good EFI setup.

[sprowley]

Originally Posted by Cross

I did not look for anything older than a 91 due to the fuel injection. There was no way I was going to deal with having a carb. Not to mention off roading the fuel injection performs a lot better.

4.0's came in XJ's since 86 I believe though, so there are a good number of spare non-HO 4.0's out there, even though they didn't start life in a Wrangler.

[wendell]

In 91 they improved the head, cam and efi set up and called it HO. Before 91 they used the franch efi system and the head was about as good as the 258. However, the non HO 4.0 wasn't a sloutch at 77 hp and good torque numbers, but it had the weird tb that was hard to upgrade or do anything with except port it.

[Whitey2001]

I have a '90 Non-HO that I am stroking to 4.7L. It does have a weird TB that I bored out to 60mm and had to JB Weld the wall because it was so thin. It is a P.I.T.A. to find performance parts for the Non-HO. If you can find parts, they are 2-3 times more expensive than for the HO engines. I chose the Renix engine partly because of price, but also for the knock sensor. I plan on running a compression ratio of 10.2:1 so that I can use e85. In case I can't find e85, I wanted my computer to have the ability to adjust timing to reduce knocking while on regular gas. I did have to port the head, but with everything I am doing to it, I expect to get 230-250 HP out of it.

[Mobile_Homie]

Get a 91 or later 4.0 HO and don't look back just my $.02
Happy Wheelin'

[90yjkrawler]

Originally Posted by Whitey2001

I chose the Renix engine partly because of price, but also for the knock sensor. I plan on running a compression ratio of 10.2:1 so that I can use e85. In case I can't find e85, I wanted my computer to have the ability to adjust timing to reduce knocking while on regular gas.

Whats a knock senser? Is that something that adjusts the fuel pres or air fuel ratio? The HO 4.0L doesn't have this?

[Mean Max]

Originally Posted by 90yjkrawler

Whats a knock senser? Is that something that adjusts the fuel pres or air fuel ratio? The HO 4.0L doesn't have this?

A knock sensor is a block mounted sensor that detects pre-ignition knocking. It helps remedy the knocking by retarding the ignition.

[dukegnarley]

i have a renix 4.0 in my yj. I also cry myself to sleep at night.

[ech0sh4y]

how can you tell if you have a Ho or not?

[dukegnarley]

wranglers didn't come with the renix. the only way you'd have one is if someone swapped one in. the renix engines have the throttle connect on the back side of the throttle body while the ho has it connect on the front side of the throttle body.

[ech0sh4y]

so all post '90 4.0L, if not swapped out previous, are H.O. motors?