4.0 throttle body upgrade to 2.5 L

[JeepFan555]

ChromeTJ was saying something about putting a 4.0 throttle body on my 2.5 L which would give it more power. Anybody know anything about this?

[jps4jeep]

Yes, just a little, but finding one is gonna be hard! most places that sell New TB's require a Core Replacement.

I think they are
4cyl - 56mm
6cyl - 58mm

[chrometj]

Here's that write-up for the TB swap...

ericasworld.logic.net/index.php/Throttle%20Body

you may be able to find more on the internet, I think I have some in my favorites but that one was the best one..(I don't know how accurate those numbers are but quite a few people do this mod with the 2.5L, so I have read...)

Look for 4.0 throttle bodies on ebay...Im sure you could get one from a cherokee as well as they are identical (right??)

Mike

[mikeswrangler]

Salvage Yard time. You can find tons of them. Then just clean the sh*t out of it. If you cant find one where you are let me know I can get one around here for cheap.

[JeepFan555]

Not a bad deal for 24 hp thats nuts. I am going to look into it for the summer cause thats when Ill have money

[chrometj]

Jeepfan555 said:

Not a bad deal for 24 hp thats nuts. I am going to look into it for the summer cause thats when Ill have money

actually its kinda expensive...the throttle body itself is only like 6hp gain, thats with the spacer too! spacer=100 dollars not including the throttle body...there are a few guys online who make custom spacers and theyre not much money, I dont see a difference between theirs and performance ones in magazines, i hear the helix ones are a load of crap, just go smooth...

24 hp, keep in mind this jeep has more mods "Finally, should say that the TJ has a two-stage K&N filter system, an MSD ignition system & coil, high-gapped Champion truck plugs, a Flowmaster delta-40 catback, and a case-full of Mobil 1 synthetic oil. All or part of which may have a synergistic effect on my results, since mods usually affect each other.".............all of these have effects on each other!!!!

[chrometj]

a post on jeepsunlimited about that throttle body swap:

www.jeepsunlimited.com/forums/showthread.php?s=&threadid=630158

[ZAEDOCK]

I just finished installing another 2.5L into my SM420/NP231HD equipped '92 YJ a few weeks ago.
I had previously installed a TB spacer but found that it hurt performance. This time around, I removed the intake manifold and cut away the 1/8" lip that the intake overhangs after installing the spacer. I also opened up the TB a little at the bottom and ground the screws that hold the throttle plate in for more air flow.

After installing it all, I have noticed a "seat of the pants" improvement. I can also hold hills better.

The best bang for the buck is a TB spacer with the intake ground away to open it up correctly. Just remember to make sure you completely clean the intake before reassembly.

[jps4jeep]

I have to agree with Joe that I would perfer to simply modify my factory TB before I shell out any $$ on a after market or replacement for a bigger bore. All the after market units are, are factory TB's over bored at the base.

Off topic

Joe, I will be putting a sm 420 into my 94 yj but will be a 6cyl in front of it. The tranny is comming out of my old Chevy truck, and was rebuilt right before I took the chevy off the road. I found the adapter for the Tranny-Tcase, can't find one for Motor-Tranny? Also what is it like on the highway, 60mph revving 3000rpm?

[ZAEDOCK]

Here is a post that might be able to help you : www.jeeps-offroad.com/showthread.php?t=4740

To my knowledge, there isn't a factory bellhousing to mate a 4.0L to a SM420, but I wasn't really looking for one. You may get lucky. Look to Advance Adapters or Novak if you can't find a factory one.

As you probably know, the AMC (Jeep) 2.5L has a 60* Chevy bellhousing pattern, so I used a bellhousing from a 1986 S10 pickup with a 2.8L & 5 speed. The bellhousing bolts to the engine and tranny like it was factory. The only things I had to modify was to cut a little for the starter to fit and fab a mount for the crank position sensor (which was no big deal). I also have the benefit of using the external slave cylinder from the S10.
I bought an adapter from Advance Adapters to mate the SM420 to my 1/2 ton Dodge truck NP231HD from JB Conversions.

As far as highway RPM's go...four cylinders need to rev a little higher than a six, but expect about 3000-3250 RPM if you run 4.10's - 4.88's and a 33" to 35" tire. Personally, I only put about 800-1000 miles a year on my YJ so highway driveability is low on the list. My YJ comfortably cruises at 65-70mph.
As soon as you throw it into low range and use the tranny's 7.05:1 first gear on the trail, you'll forget all about the highway drive there...

Joe

[JeepFan555]

thanks guys I'll check it out