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Thread: 4.0 differences 87-90 91-up

  1. #1
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    Default 4.0 differences 87-90 91-up

    I was wondering what is the difference is between the 4.0s. I know the 87-88 had 150HP the 89-90 had 175HP and the 91+ had 190, whats the reason for the increase? Was it internal engine or something with the fuel injection? I know the 91+ fuel injection is suppose tp be better, but why? How is it different from the older style? Just wondering so that i can plan what i need to do when i rebuild or change out my engine.
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    The horsepower gains in 91 are from the head, intake, throttle body and exhaust manifold. It really has nothing to so with the fuel injection.

    I kinda think that the non-ho fuel injection is better than the HO fuel injection simply becauser the non-ho (renix) fuel injection uses a knock sensor to run the timing as advanced as possible. This, combined with the HO head intake and exhaust would be the best combo.
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  3. #3

    Default 88xj

    i hope you don't mind me posting another question on top of your question... but i have an 88xj pioneer... and on the back it says it has a 4.0l high output... i thought they didn't put a HO engine into the xj's until early 90's... i know the previous owner had new rebuilt engine put into it.. does this mean he put a newer (90s on) engine in it or is this normal for 88xjs?
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  4. #4

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    This is from Dino's site http://www.jeep4.0performance.4mg.com/


    '87-'90: 177hp at 4500rpm, 224lbft at 2400rpm, redline 5000rpm
    '91-'95: 190hp at 4750rpm, 225lbft at 3950rpm, redline 5250rpm
    '96-'99: 190hp at 4600rpm, 225lbft at 3000rpm, redline 5300rpm
    '00-'01: 193hp at 4600rpm, 231lbft at 3000rpm, redline 5300rpm

    The reasons for the increases are probably due to machining refinements, increases in compression, computer upgrades, balance refinement, smoother intakes, better throttle bodies, and higher flow injectors.
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    rl

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    Default Re: 4.0 differences 87-90 91-up

    Originally posted by orange02SS
    I was wondering what is the difference is between the 4.0s. I know the 87-88 had 150HP the 89-90 had 175HP and the 91+ had 190, whats the reason for the increase? Was it internal engine or something with the fuel injection? I know the 91+ fuel injection is suppose tp be better, but why? How is it different from the older style? Just wondering so that i can plan what i need to do when i rebuild or change out my engine.
    all 87-90 4.0s had 177 hp, i know thats not what 4wd&su says, but its the truth

    1337 is right, but basically everything he described WAS fuel injection

    vlad, your going to have to post pics of this...87-90's had "low"outputs, he could have swappen in a ho, but i dont think hed swap the emblems, thats some work for just that...check out your tb, how many bolts does it have? how is the air intak tube secured?
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    Default

    They didnt have the HO until later so maybe he put one in for you.

    As for the throttle body on the newer ones, is it hard to swap new stuff on to older models? How much modding needs to be done? anybody else have more info?
    88 XJ Limited
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    Default

    Orange ....... the 87-88 motors made 177 hp. Just like the 89-90 motors. Not sure where you found that info. <shrug>

    In 91 ..... the computer was changed. Port angles changed. Port sizes modified. Better exhaust manifold. And some other little trinkets. That's where the 13 hp gain is.

    Vlad ...... he prolly just put a sticker/badge on it.

    It doesn't take much to get the Renix motor to make very similar power to the HO. Because the HO is more "efficient" in making power ... it doesn't respond *as much* to basic hotrodding (like intake & exhaust).

    But the gains are there. I wouldn't go nuts swapping if you have a good rebuildable motor. Just buy the peripheals that will give you the gains.

    Joe

  8. #8

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    hjeepxj.... what should i look for on the tb? what would be the difference (of low vs high output)? i can't (or i should say i won't) go out tonite and check... i'm in CO and it's been snowing and its freezing outside and i can't pull my jeep into the garage tonite to check... but i'll check it out tomorrow.. maybe take some pics, etc
    jason
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    Default Re: Re: 4.0 differences 87-90 91-up

    Originally posted by hjeepxj
    all 87-90 4.0s had 177 hp, i know thats not what 4wd&su says, but its the truth
    I was wondering about that in this months issue, but 4wd&su didn't quote their source on the 150hp spec.

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  10. #10
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    http://www.off-road.com/jeep/cheroke...p/engswap.html

    If you need more info just do a search here or on the 'speed freaks' forum. I know I have a couple posts about it. I just need a HO throttle body to start the swap of a 93 into my 87.

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    Default

    Originally posted by vladthedog
    hjeepxj.... what should i look for on the tb? what would be the difference (of low vs high output)? i can't (or i should say i won't) go out tonite and check... i'm in CO and it's been snowing and its freezing outside and i can't pull my jeep into the garage tonite to check... but i'll check it out tomorrow.. maybe take some pics, etc
    jason
    it is freezing! im in co too, i think i pmed you

    you should look for if the ai boot is secured by bolts or by a hose clamp, and look and see how many bolts secure the tb

    if the ai boot has a hose clamp: it is a ho, as well as 4 bolts to secure the tb

    if the ai boot is bolted with three bolts, and when you take it off you see 3 bolts securing the tb, you have a non ho
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