87 to 89; difference in hp.

[Mike1331]

So I just bought a fresh 87 after I sold my 89 to a buddy. I'll get some pics for u guys this thing was well maintained, Its a laredo with a d44 auto everything (which Im not to extatic about) rebuilt tranny and engine new radiator water pump paint job factory skid plates all around heres the link brahttp://www.craigslist.org/sby/car/74019533.htmlkes
Just looked at the smog certificate and it passed w/ flying colors Chasis has a total of 165,000miles on it and it feels like more solid of a truck than my friends old 96. Its lacks a lot of power from newer years now I know the bore and stroke are slightly lower in these earlier models could that account for the 27 more horspower that the 89 had or were the intake and exauhst ports smaller along w/ the other intake components. Im going to by a head and port it pretty soon and do as many other bolt ons as pocket alows after I lift it.
So heres the real question my buddy is putting a stroker kit in the 89 and the pistons are in great condition would swapping those and the rods acount for the lost bore and stroke for an increase in hp and compression

 

[Mike1331]

anybody got any thoughts?

 

[Eagle]

The bore and the stroke are the same for all years of the 4.0L.

The horsepower differences are due to advances in ignition and injection, and the redesign of the head and manifolds. However, your '87 produces its peak torque at a much more real-world usable RPM of about 2400, compared to a torque peak of about 4000 RPM for the HO engines. Yours probably also gets better gas mileage, unless you flog it trying to make up for the lower horsepower.

 

[Mike1331]

Really? I thought the starter might be going out but it must be poor spark coming from the ignition would aftermarket ignitions help this out at all? Are they affered for 87 I have only found em for 91 and up. So by advances in fuel injection are you saying the injectors are flowing at a low rate like 15Lb/hr or sompten hanusly low ultimately forcing me to get some larger ones to prevent from runnen lean when I do intake upgrades.

 

[NotMatt]

87 and 89 are, for most parts, the same as far as the engine goes... where did you get the 27hp difference number? Both motors use the RENIX EFI system and both have the same R/S ratio (infact all 4.0's do).

The stock injectors should do you fine unless you're going to build a stroker like your buddy... they computer can compenstate somewhat for higher air flow or denser air.

You mentioned something about weak spark... is the rig not running? Not turning over or starting? The starter has nothing to do with the spark output, all it does is crank the motor over. If it's cranking and does not fire, look at the CPS first... plug and unplug the connector for it (near the firewall next to the valve cover on the driver's side, wires run down behind the head to the bellhousing), they get corroded and will prevent the CPS signal from getting to the computer, causing it not to start.

You've got almost the same model my rig started out as... 87 laredo, factory D44, all power options (except seats). Something to think about for those who are looking for a factory 44... seems like they used them a lot in 87 on the decked out models.

 

[Mike1331]

The rig is running strong as an ox but it has trouble starting, it turns over more times than any other cherokee ive heard start, once it does fire up the compression sounds perfect and it turns off smoothly w/out any deiseling. I was thinken the ignition might be the issue w/ spark output not the starter. As far as the difference in horses go my buddy pulled that out of a owners manual, said the stroke on the 84-87s were .2or.3 less along w/ the compression ratio. Stock specs for mine were 150hp and the 89 was 177hp.

 

[Eagle]

All Renix XJs take several turns before they fire. It's designed into them.

The injectors are 19.6 pounds/hour and they are designed for the engine. If you make major mods, like an open intake combined with a cam, you might need to step up to the next larger size, but that's not due to a problem, it's due to the fact that they are specified to run correctly with the stock engine.

Before you start throwing money at mods that are going to make your Jeep run worse instead of better, I strongly advise you to jump over to the Street & Performance forum here at and get yourself in touch with Dr. Dyno. It sounds to me like you don't understand how an engine works, and that to you everything is a "problem" requiring a "fix."

For example, don't bother with aftermarket ignition "upgrades." The factory system is already a high-energy system. The only thing that will benefit from an aftermarket system is the bank account of whoever sells it to you. Put in a good set of NGK non-platinum plugs and a set of Magne-Core plug wires and call it done.

 

[NotMatt]

The rig is running strong as an ox but it has trouble starting, it turns over more times than any other cherokee ive heard start, once it does fire up the compression sounds perfect and it turns off smoothly w/out any deiseling. I was thinken the ignition might be the issue w/ spark output not the starter. As far as the difference in horses go my buddy pulled that out of a owners manual, said the stroke on the 84-87s were .2or.3 less along w/ the compression ratio. Stock specs for mine were 150hp and the 89 was 177hp.

No such thing as a 4.0 before 87, at least not in a cherokee. Sounds like maybe you're comparing apples to oranges (2.5L I4 or 2.8L V6 to the 4.0L I6).

Renix 4.0's take a while to crank over, it's just that way. The CPS needs a few revolutions to get a good reading, it's normal.

 

[Mike1331]

I am simply comparing it to other Cherokees ive seen because its all I have at this time I don't have much experiance or guidence I am just now getting into them and am now already an enthusiust, sorry if my questions are too jouvenile for you. Of course im not going to fix anything that is not broken hence the reason of coming hear first to make sure everything is kosher. I am ultimatly hoping to build a rig that is jeep-speed capable so in that perspective street performance forums don'y sound like a bad idea thanx nomatt didn't know I got the first 4.0 available in cherokees, learn sompten new everday.

 

[alosix]

The older Renix setups do take a while to start, even when brand spanking new. Make sure your Crank and Cam position sensors are happy, that may help a little.

If its running strong, why mess with it? I doubt I'd really trust the 27 hp difference between factory specs. The factory has been known to lie on those numbers, half of the time making the early years a good bit lower than what they actually put out so they can raise it on the sticker without having to mess with the design the next year.

Newer TJs claim 10hp over the older TJs yet tend to feel slower when driven.

Jason

 

[Eagle]

The difference isn't 27 horsepower in any event. The '87 was rated at 173 HP, the 88 thru 90 were rated at 177. The HO came out in 1991 rated at 190 HP. So the difference is either 13 or 17 HP, not 27. Torque rating remained virtually equal, but the torque peak on the arly HOs was at too high an RPM to be useful.

 

[Ramsey]

was the torque curve moved lower on later model HO's?

 

[NOVAggie]

The difference isn't 27 horsepower in any event. The '87 was rated at 173 HP, the 88 thru 90 were rated at 177. The HO came out in 1991 rated at 190 HP. So the difference is either 13 or 17 HP, not 27. Torque rating remained virtually equal, but the torque peak on the arly HOs was at too high an RPM to be useful.

So it sounds like an 87-90 would be the best bet for a good solid 4.0 with usable power??

 

[old_man]

If you are feeling a big difference in power, make sure that both rigs had the same gear ratio. It isn't uncommon to have different gear ratios in different jeeps.

 

[Eagle]

was the torque curve moved lower on later model HO's?

Yes, somewhere in the late 90's they dropped it back to 3500 or 3200 RPM and squeezed a couple of extra foot pounds out of it.