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Thread: 2.5 to 4.0

  1. #1
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    2.5 to 4.0

    i hate my 4cylender. its great wheeling its just the road driving that blows.
    im trying to talk myself into the swap, money isnt an issue..its just space...and the damn cold also lacking a bit of motivation to be honset. iv got alot of free time on my hands but its so cold i would rather do the swap in the summer, when im working full time....and need a dd.
    If im going to do this, im going to buy a complete jeep, and use the motor and tranny, iv got a 231 d300 doubler in the jeep so i plan on using it. but im aware of all the mechanical and physical install issues. its just the wiring thats intimidating me.

    its a 98 TJ. and reusing the dash isnt a big deal, i would love to put a CJ flat dash in. iv got 35's on it now with the stock 4:10's...i plan on going much bigger and the motor is the weakest link right now.

    i might add, id love to not do any of this and put money away for a house, but this swap im planning on doing for under 1000

    HELP ME DECIDE
    love my 2.5

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    i have also got a 2.5l
    and well i have no intentions of swapping it....
    Richard
    13 JK Sahara Unlimited

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    Personally, if I were to do a motor swap I'd be going for something with more spunk than a 4.0, especially if I planned on eventually making the Jeep huge.

    On that note, I'd be doing my homework and look into a 318/350 or something like that.




    LC.
    So I installed the flux capacitor but the Jeep just won't do 88 mph.

    - '97 TJ, 4" Superlift, 33" SSRs, lunchboxed rear, 12K Titan, and 2.5 litres of exhillirating performance

    - '99 WJ Limited 4.7, 2" RC BB, 31" Mall-Terrains, Pavement Princess

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    What sort of shape is your current Jeep in? Would you be able to sell the 2.5L and buy another jeep with the 4.0L in it and then swap all the stuff you want to have on the 4.0L jeep.
    That was my route.

    If your buying a 4.0L Jeep complete I wouldn't be too worried about the wiring, just swap everything over from the donor vehicle. However the list of things that requires change can get pretty impressive.

    If you have a np231 in your 4cyl Jeep now then it has a 21 spline input shaft, the 4.0L would need a 23 spline input shaft, agian not a huge deal just another item to add to the list.

    What about another type of engine/ tranny altogether?

    I bet I'm not helping much!
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    Quote Originally Posted by WuMark View Post
    ...i would love to put a CJ flat dash in...

    Do it! ...then show me how you did it. Even a YJ dash would be far cooler than the minivan-dash in the TJ.



    Also, with even a 4.0 with 35s and 4.11, those axles are going to be easy to snap. Perhaps keep axles in mind while looking for a donor vehicle.





    LC.

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    belive me, all these things i have thought of. from what iv been reading places 350 and 4.0L are very much alike in the power range? stock to stock. but i would like to put a V8 in also, fuel milege isnt a issue to me at all really...and i would like to take advantage of my care free attitude lol

    i would love to buy a CJ with a 302 or 360 in it already but there just isnt anything going up forsale lately and i have been watching. but then there is the question of selling my jeep, i feel i have put too much money into it to sell.....although i would like to sell it if i found the right CJ. i love the simplicity of leaf springs, and would much rather have leafs than stock 4links

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    if i bought a CJ, i would be putting 1Tons in it shortly after im sure.

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    By the way, is this a DD or a toy? That would change everything.

    I don't have numbers to back this up, but I would imagine a stock 350 puts out oodles more torque at lower RPMs. Horsepower may be close.

    I guess you'd have to e-test this thing too. No matter what motor I'd go for, I'd make sure it's fuel-injected. The last thing I'd want in a rig (or anything) is having to screw around with carb settings and stalling it on steep hills.




    LC.

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    this is a DD. i think im putting my foot down on the swap, aand finalizing that i want a CJ. the question is still up what to do with the 4pooper TJ...i cant have 2 vehicles in the driveway, father wont allow it!

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    Re gear to 4.88's and call it a day. Buy a 6cyl TJ and start from scratch. Your issue right no is the fact you have the wrong gears for the tire size you are running.
    Poster does not represent or warrant the the information accessible via this post is accurate or complete. Except as specifically stated on this post, neither rbjeepthing nor any of his affiliates, will be liable for damages arising out of or in connection with the use of this post.

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    i cant understand how gearing is the fix. will it just not be reving higher all the time ill be in fifth crusing at 80 with the rpm's at 4grand?

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    can somebody move this to technical talk, my mistake.

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    ^not on 35's. The lack of power is due to a few things. Weight, Gearing, Drag (Arrow Dynamics/Rolling Resistance) and the only way to gain this back is to go to the correct gearing. Your final drive ratio is severly comprimised do to your tire size right now. I don't really know an easy way of explaingin it unless your a mathmatician.

    Specs for a 4cyl Jeep

    4.10's = 29" Tire
    4.56's = 31's/33's Tire
    4.88's = 33's/35's Tire

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    yeah buddy, just regear, RBjeep is bang on. Try some power add ons, intake exhaust, blower whatever you want. Engine swaps are a PITA the first time around and thats a sweet jeep you got there. my $0.02
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    iv been reading up on doing the gear swap on my own, im confident i can make it happen properly.

    my new question, will i fit 4:88's on the front carrier and the rear detroit ?

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    i think 456's is the highest for that carrier, still cheaper than a motor swap though.

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    i hear ya. how signifiant of a difference will it be? i have never expearianced a jeep that was regeard

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    if done right it will be like driving a stock jeep, but you will be on 35's. My buddy runs 410's in his 4.0 yj on 35's and its better than stock. The tranny gearing and power output are obviously different in a 4.0

  19. #19
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    Quote Originally Posted by Chevy YJ View Post
    i think 456's is the highest for that carrier, still cheaper than a motor swap though.

    Nope, I know you can't definately go 4.88 with that carrier, but I think that's the limit.

    Wu, the reason you have to regear after adding larger tires is because the larger circumference tires are making the Jeep travel farther with each rotation. That means to add larger tires and go the same speed, the engine has to run slower.

    Here's a good chart showing optimal gearing vs. tire size:

    http://www.4lo.com/calc/geartable.htm





    LC.

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    is the downfall that my top speed will be less (not that, that matters)? or is there no downfall at all, i just can grasp my head around how gearing fixes it, but if it dose...i guess ill have to trust you guys! i acually just got a price for gears the other day, not as expensive as i thought.

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