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General Forums => The Mess Hall => Topic started by: fireman411 on May 10, 2010, 09:53:46 AM

Title: 2.5 tbi to 4.0
Post by: fireman411 on May 10, 2010, 09:53:46 AM

ok. I have a few questions. I just bought a 90' yj 2.5 tbi and want to upgrad to a 4.0.

What would I need to make this happen?
Can I purchase a donor xj and use the motor and drivetrain from it?
If I have 4.88 gears, would I need to change those out?

I am lost and need some guidance.

Title: Re: 2.5 tbi to 4.0
Post by: Jeffy on May 10, 2010, 11:41:48 AM

I would look for a 4.0L YJ and pull everything from it.  Gas tank, engine, radiator, tachometer, harness, PCM, transfer case, frame mounts...  An XJ Donor won't give you the gas tank, tach and frame mounts.  Although, you might just find it easier to get a 4.0L YJ and swap your parts onto it.  That would be a lot less headaches.

I'd stay away from a '87-'90 XJ Renix 4.0L.

Title: Re: 2.5 tbi to 4.0
Post by: TrailsLessTaken on May 10, 2010, 01:21:03 PM

I second Jeffy, it would be alot less work to swap your parts on to a 4.0 wrangler then to swap everything else

Title: Re: 2.5 tbi to 4.0
Post by: Torch_Ind on May 10, 2010, 04:34:15 PM

whats wrong with the 4cld?

Title: Re: 2.5 tbi to 4.0
Post by: fireman411 on May 10, 2010, 05:45:59 PM

the four cyl isn't bad but it doesnt get good gas mileage. I was thinking of changing the gears to a 4.88 but i dont know if that will help or not.

 I am really lost with this lol :confused:

Title: Re: 2.5 tbi to 4.0
Post by: FourbangerYJ on May 10, 2010, 06:08:16 PM

Quote from: fireman411 on May 10, 2010, 05:45:59 PM

the four cyl isn't bad but it doesnt get good gas mileage. I was thinking of changing the gears to a 4.88 but i dont know if that will help or not.

 I am really lost with this lol :confused:

Gearing to 4.88's will be a big help. The problem with the pre 91 motors is there is not really much in the way of power adders such as the TB,injectors,adjustable fuel pressure regulator.
If your wanting good mileage a Jeep is not what you should be driving. ;)

Title: Re: 2.5 tbi to 4.0
Post by: Torch_Ind on May 10, 2010, 07:03:14 PM

Quote

If your wanting good mileage a Jeep is not what you should be driving. Wink

my g/f has a 99 honda civic hatch dx thats the way to go if you want miles/gallon

going six won't be any better miles/gallon it will be roughly the same but you will have more power. if you drive high speed it will be worse then the 4cld.


if you want a 4x4 your not going to get much better miles/gallon.  even my ridgeline I had was in the 25mpgs range TOPS highway!! if you were very LITE footed. if you speed you will burn fuel!!

long trips that we want to save on fuel we drive her little car!!