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Old 09-08-2008, 01:52 PM
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Best engine?

I am getting ready to replace the 4cyl engine in my YJ with an I6, not sure if I should go with the 4.0 or 4.2? Any thoughts or suggestions?

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Old 09-08-2008, 01:59 PM   #2
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there's not even a discussion here. 4.0 its a big improvement over the earlier 4.2 with fuel injection and more horsepower. and it is built on the same platform, it took all the good parts of the 4.2 and made it fuel injected. almost identical blocks and heads.

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Old 09-08-2008, 08:07 PM
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I can get a 4.2 for $300 from an 89YJ. With a master rebuild kit, I could have the whole thing rebuilt and installed for about $800. I can't seem to find any 4.0's readily available, what you guys think?
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Old 09-08-2008, 08:24 PM   #4
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I'll bet you there are plenty of cherokee's at your local junk yark....they run a 4.0 too.
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Old 09-08-2008, 09:43 PM   #5
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i bought 4.0 for the stroker i'm putting in my 87 yj. i bought the complete engine, w/ all accessories alt. p/s, a/c etc, with complete wiring, all manifolds, injectors, computer, fan, pulleys, even a newer radiator for $400. everything you need to swap engines, ebay is a good thing.
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Old 09-09-2008, 03:27 PM   #6
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i bought a complete good running cherokee with the 4.0 for 150 bucks.
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Old 09-09-2008, 04:02 PM
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Well it seems damn near impossible to find a 4.0 in this area, so I am thinking putting a Chevy small block. How much of a PITA is the conversion?
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Old 09-09-2008, 04:40 PM   #8
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From all the reading and talking to guys that did it first hand, they say that the hardest engine swaps into a Jeep are, get this..... JEEP MOTORS.

I know a couple of guys who swapped in 4.0's after there 4cyl crapped out on them. Most of them said if they had to do it over again, they would have just went with a V8.
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Old 09-09-2008, 09:03 PM   #9
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yeah but take it from me, putting a chvy small block into a jeep IS NOT CHEAP! i'll do this as short as possible...unless your putting in a known running v8, building one cost me up wards of $2,500.00 with me building it. mounting it cost $250.00 cooling it cost $400.00 drive train cost $1,000.00 (i built a TH400) chvy t-case w/ SYE cost $500.00 (i built and installed)custom shaft cost $300.00 i cant even put in a front shaft yet...ran outta money. and i'll still need to buy/fabricate a 8.8 ford rear end so the v8 wont shred my D35. but on the upside i will produce 300 hp, and swapping from a hugely under powered 2.5L i'll even get better gas mileage. ohh and throw in a few hundred bucks for wireing it all up and stuff like distributor, ignition, the list keeps going. about 6-7K to do the job right. im not bummed i did it, just poor as hell now. and im now due for new [email protected] $300.00 a tire im cryin'
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Old 09-10-2008, 07:16 AM   #10
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From all the reading and talking to guys that did it first hand, they say that the hardest engine swaps into a Jeep are, get this..... JEEP MOTORS.

I know a couple of guys who swapped in 4.0's after there 4cyl crapped out on them. Most of them said if they had to do it over again, they would have just went with a V8.

and are you comparing a carbed v8 to a fuel injected 4.0? slappin in a carbed motor will be easier in the aspect of wiring and computers. but fuel injection is much better.
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Old 09-10-2008, 11:33 AM   #11
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injected is more fuel efficient than carb yes, but im also installing a propane "dual fuels" which injected would not allow me. one cylinder of lpg is like an extra 9-10 gal of gas. i'll be able to mount two. plus run reg gas.
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Old 09-10-2008, 02:25 PM   #12
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and are you comparing a carbed v8 to a fuel injected 4.0? slappin in a carbed motor will be easier in the aspect of wiring and computers. but fuel injection is much better.
I didn't say anything about a carb.

When doing an engine swap in most states(or all) you need to install a motor that is from the same year or newer vehicle. If his YJ is even an 89, any other motor is going to have wiring to install. Getting an even newer motor, like a 2003 5.3L Chevy would be simpler because of the newer and more refined electronics in the system.

Again, this is what I have heard from guys that have done it first hand, not myself. Although I do plan on V8 power later on in my TJ's life.

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Old 09-10-2008, 02:59 PM
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I am still confused about the entire "wiring" issue, it seems to me that no matter which motor I put in I will have to change the wiring harness unless I put in the exact same motor from the exact same year. The rig originally had the I6, the previous owner put the 2.5 in there. At this point I am not sure which motor I want, but I don't believe I want a fuel injected motor.
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Old 09-10-2008, 04:57 PM   #14
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I am still confused about the entire "wiring" issue, it seems to me that no matter which motor I put in I will have to change the wiring harness unless I put in the exact same motor from the exact same year. The rig originally had the I6, the previous owner put the 2.5 in there. At this point I am not sure which motor I want, but I don't believe I want a fuel injected motor.
first of all go kick that guys behind for putting a 4 cyl in place of the 4.0.

secondly, yes you'll have to have a wiring harness for any engine, but a plane ol carbed 350 has very little wiring, and would be a lot easier than putting in a 4.0 with 10 times the wires sensors, and computer.

thats all i was getting at w/ carbed vs fuel injected.
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Old 09-10-2008, 05:34 PM
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So I am sure by now everyone is thinking I am being a PITA, but I was told if I am going to go with the Chevy small block, that the 350 is way better than the 305 for both power and fuel mileage? Any thoughts or first hand knowledge of this?
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Old 09-10-2008, 05:53 PM   #16
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they use the same block, obviously 350 is bigger better and stronger. might as well do 350.

do yourself a favor and at least get a throttle body fuel injection, or use a fuel injected donor vehicle
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Old 09-13-2008, 10:28 AM   #17
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yep, the only wiring i have w/ an 84' 5.7L 350 block is ground straps, alt. to battery,dist. to ignition, i gotta figure out hooking my np 241 up (but im sure that will be simple, just havent checked yet) or i'll just put 4hi-4lo-n marks on the trans tunnel next to the t-case stick. and an electric fuel pump. gauges, and wiring to circut panel. thats about it. michigan doesnt have emissions testing, so if i could figure out how to put a FOKKER rolls royce bi-plane motor in i could....other than some hard ass cop.
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Old 09-13-2008, 10:34 AM   #18
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i always thought it would be kool as hell to start your rig by firing a shotgun primer to ignite the first cylinder. stupid i know, but it would be neat. the hard part would be turning your crank to number one each start. i'll shut up
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Old 09-13-2008, 02:34 PM   #19
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Go with the 4bt cummins diesel. 30 mpg ftw
by the way my 4.2 sucked
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Old 09-14-2008, 09:18 AM
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Well I picked up a damn nice 305, and am currently in the process of adding all the new pieces (ie. water pump, P/S pump, plugs, wires, entire gasket kit, altenator, headbolts, and a bunch of other minor stuff)

After a full day of putting this back together I went to order my conversion bellhousing only to find out that the transmission I have will not bolt up to a Chevy motor. So anyone know of a good transmission to get? I read the AX15 is a medium duty tranny, and the conversion bellhousing is available. I have also been thinking about just putting a Chevy tranny in and adapting to the transfer case? Any thoughts?
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Old 09-14-2008, 09:29 AM   #21
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i have heard people that used the ax15. the guy i bought my 4.0 off of put a 350 in and kept the ax15 trans. that trans will be easy to find, it came stock in wranglers with the 4.0 since around 89 or so thru most tj years i believe, till they replaced it with the nv3550

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