motor of choice

i've got an '87 4.2L with just over 200k and i was thinking about doing a motor swap. but i'm not sure if i should just put the 4.0 heads on it or switch over to the 4.0 altogether. OR should i look for a GMC replacement. i don't want to use a 350, although it would be awesome, because i don't want to replace my whole drivetrain or pay for the gas. what do you guys think? TIA

If you do decide to go with a 350, adapters are available to keep the stock transmission and transfer case. If you have an AX5 tranny, it will handle the 350. If you have a Peugot tranny, burn it. About gas mileage: My 4.0 got 14.2 mpg over 140,000 miles. My 5.7 (Corvette) in the YJ gets 14.4 mpg.

WHOOPS! I named the wrong tranny. It is the AX-15 that will handle a 350.

Personally I like the I-6, thats all I have run in my CJ's for years and have a pretty good background with them. Most of them will run 350,000 or more miles with good care. I know my CJ-8 and 7 have both run over that many before being rebuilt. Now as far as power it doesnt have anything near the V-8 conversions or even the 304 that came stock in earlier model CJ's but it gets the job done just the same. I've even found that my I-6 has out performed several V-8 jeeps on the trail with no problem, but all that comes down to how you drive off road.

I'm a big fan of the inline six also; a rebuild with a mild cam to make more torque would be my preference; yeah, V-8 is loud and all that, but you can get good power out of the 4.2

I have a 90 with a 4.2. Runs fine in town but on the highway it has no power. Hills of western pa slow me down to under 60 mph. Is that normal or do I have an engine problem? It has a new weber carb, and Borla headers. Rebuilt the engine about 50 K ago but no real change with any of the modifications. I love the jeep but my daughters 91 grand am 4 cylinder will fly on the highway! Any ideas?

Im not sure but have you checked the gear ratios, maybe they're off. If you have larger tires that could be your problem. Thats just my 2 cents though.

Im not sure but have you checked the gear ratios, maybe they're off. If you have larger tires that could be your problem. Thats just my 2 cents though.


Stay with the 4.0-otherwise you will run into huge $$$

The ax-15 will not hande a 350-even if you did a 350 swap-and I have done 3 in a wrnagler/cj7 now-you would be better off selling the ax-15 and tcase and picking up a nice sm465 or similar stick tranny-or I suggest a th350 auto tranny. Stay with teh fuel injection-if you go to carburatation-swap on a motorcraft 2100 or autolite 2100 or 2150 series carb. I would stay with your 4.0-get a nice header and free flowing exhaust. I am been through the other swaps like 4.3 and 350 or 305-it just gets expensive...

Hey Aereo,
ive got an 88 yj with a AMC 150 Fuel Injected and an AX-5 tranny and a 231 t-case. I m swaping that for a 4.2L I6 and i m modifying the engine a lil i am getting the whole drive line from an 89 wrangler and i m goin to rebuild the I6 with the head, the intake manifold, fuel injectors and computer for an 1996 H.O. 4.0L and im goin to put a medium cam, new pistons and mayb even stroke it out a lil more you will get more power for less modications if you go this way a big v-8 will cost you so much for motor mounts, tranny, t-case, and driveshafts. Your best bet is to do some work to the 4.2L i mean if you fuel inject it u will how more power and torque then a 4.0L 4.2L are motors that r under powerred stock so a cam and the fuelinjection willl solve ur ned for more power and if u rebuild the motor u will get the mileage u want so jus do yourself a favor and keeep the I6 dont jus swap over to the 4.0L you already have a ,motor stroked out more than the 4.0L and if you modify it right you canget alot more out of her well if you have any questions feel free to email,IM, or post a reply ill be checkin in on u my friend good luck jus take this into consideration.

Get 'er Dun
wrangler88yj AKA Sarge

Yes i loved my 4.2 after I got rid of the carter and switched to a weber. I also added a TFI ingition and bypassed the emu.. I sold it to a friend at work and he still loves the thing and it runs smooth.I ran mobil 1 5w 30 it was smooth and quiet until you put in low 4 wd and it took off..with a nice grunt. MAN I miss it. the emu was called the nutter bypass if you punch it on googles or a search engine it may still show up.

I have a 90 with a 4.2. Runs fine in town but on the highway it has no power. Hills of western pa slow me down to under 60 mph. Is that normal or do I have an engine problem? It has a new weber carb, and Borla headers. Rebuilt the engine about 50 K ago but no real change with any of the modifications. I love the jeep but my daughters 91 grand am 4 cylinder will fly on the highway! Any ideas?
It may not be tuned to the weber carb. engine timming etc. I would turn the timming up a little and see what happens.U can bypass the emu but not sure how on the 90 model.do u have manuel or auto tranny. I know the manuel trannys ore a little slower than the 727 and 999 auto tranny
I dont know why but they are I am sure its the ratio.

Hey Aereo,
ive got an 88 yj with a AMC 150 Fuel Injected and an AX-5 tranny and a 231 t-case. I m swaping that for a 4.2L I6 and i m modifying the engine a lil i am getting the whole drive line from an 89 wrangler and i m goin to rebuild the I6 with the head, the intake manifold, fuel injectors and computer for an 1996 H.O. 4.0L and im goin to put a medium cam, new pistons and mayb even stroke it out a lil more you will get more power for less modications if you go this way a big v-8 will cost you so much for motor mounts, tranny, t-case, and driveshafts. Your best bet is to do some work to the 4.2L i mean if you fuel inject it u will how more power and torque then a 4.0L 4.2L are motors that r under powerred stock so a cam and the fuelinjection willl solve ur ned for more power and if u rebuild the motor u will get the mileage u want so jus do yourself a favor and keeep the I6 dont jus swap over to the 4.0L you already have a ,motor stroked out more than the 4.0L and if you modify it right you canget alot more out of her well if you have any questions feel free to email,IM, or post a reply ill be checkin in on u my friend good luck jus take this into consideration.

Get 'er Dun
wrangler88yj AKA Sarge

Hey thanks a lot, I was kinda leaning that way, but I needed to hear that it was good idea. I've got another question for ya sarge, have you had any trouble with the AX-15? Mine just went out, so i'm trying to decide if I should replace it with a GM part. they're cheaper and just as (if not more) reliable. any suggestions?

hey Aereo
look i have a lil bad news to tell u ur jeep doesnt have an AX-15 tranny urs has a French peuget tranny that tranny is really prone to breakin it doesnt surprise me and your best bet is to find an AX-15 to swap tranny u willl need to get a new imput shaft for ur tranny to engine becayse the engine to peugot tranny is 21 splines and an AX-15 has 23 splines also ur gona need to get the match t-case with the AX-15 you have a np207 t-case and they r very weak if u get an AX-15 and a np231 t-caswe you will be set thats the only thing that would remedy the problem completely i think you need to look into this i would if i was you also jus send me the problems ur havin with your tranny so i can maybe let you kno how to fix the prob till u can get an AX-15 and the Ax-15 has the same bolt pattern as the peugot so you wont need to have a conversion plateany questions or comments post a reply or email me or IM me at p8ntballsarge85

got 'er did
sarge

Nope, I've already gone through the french POS, I'm now on my 2nd tranny.

hey Aereo
look i have a lil bad news to tell u ur jeep doesnt have an AX-15 tranny urs has a French peuget tranny that tranny is really prone to breakin it doesnt surprise me and your best bet is to find an AX-15 to swap tranny u willl need to get a new imput shaft for ur tranny to engine becayse the engine to peugot tranny is 21 splines and an AX-15 has 23 splines also ur gona need to get the match t-case with the AX-15 you have a np207 t-case and they r very weak if u get an AX-15 and a np231 t-caswe you will be set thats the only thing that would remedy the problem completely i think you need to look into this i would if i was you also jus send me the problems ur havin with your tranny so i can maybe let you kno how to fix the prob till u can get an AX-15 and the Ax-15 has the same bolt pattern as the peugot so you wont need to have a conversion plateany questions or comments post a reply or email me or IM me at p8ntballsarge85

got 'er did
sarge
First of all, I would like to compliment you on your ability to ignore grammar and punctuation and spelling.That's one hell of a run-on sentence.Seriously,I just have a question about one thing you said.You stated that he would need to get a new "imput" shaft for the tranny "becayse" of the different spline count.Where is he supposed to get a different shaft?who would make such a thing ,if it existed and why wouldn't he just get a new clutch,considering that is what the "imput"shaft is splined to.