2.9 to 4.0

[Newbroncossuck]

I have an 1988 ford Bronco II. I currently have a 2.9 but really want more power, I have a 4.0 sitting under the bench but I don't know if ill have to switch trannys or what all I have to do if someone smarter than me could help me.

 

[racsan]

Well the 4.0 was derived from the 2.9 , not sure ifthe earlier 2.9 trannies will hold up to a 4.0 , guess if your easy on the right pedal youd be ok. But yes-it will bolt up. You could always put lower gears in, nothing wakes up a motor like swapping out a high gear (such as a 3.45) for a low ratio ( like 4.10’s). It did wonders for my 2.3 , just get a whole assembly, put in new seals / brake parts & oil. Roll one out & roll the other one in. I feel its the best bang for the buck. Of course if your B2 is a 4wd you will need to do the front diff as well.
Welcome to t.r.s.

 

[gaz]

Newbroncossuck,

The 2.9l will be hard to beat with equal fuel economy improvements but the 4.0l will win on power numbers, with equal efficiency improvements.

ConfusU say, consider fuel economy needs vs power desires.

I love the new Bronco's, just not it's price or fuel economy

 

[SenorNoob]

In an 88, 4.0 swap is a fair bit of custom wiring if you wanna keep your dash. Almost all the mechanical bits swap though.

4.0 can be bolted to 2.9 flywheel, clutch and transmission. The 2.9 clutch will slip before you do too much damage to the transmission.

 

[lil_Blue_Ford]

So… the 4.0 will bolt up. The trans may or may not last long, but it’s easy enough to get a 4.0 trans.

The biggest thing is the wiring. You are going to have a ton of it. You need to use the 4.0 wiring and computer. You will either have to swap the dash, replace the dash harness, or splice ALL of the dash wiring to the new harness. 83-88 Rangers/Bronco II are the most difficult to do, IMHO. Lots of them have been done, so there’s plenty of information on it, and I started a swap on my 88 only to abandon the idea and change directions. Part of that was the difficulty of the swap (at the time there was a lot less information available on it), and most of it was driven by needs. My 89 needed the power from a 4.0 to drive the 35” tires. My 88 just needed a motor (resto-mod rather than lifted). 89 used the same dash harness as the Rangers that got the 4.0, so the swap was much more plug and play. My 88 is getting a lot of the goodies I’ve heard about over the years. Shift kit and other mods for the auto transmission, 2-3” of lift (enough to make it easy to work on and clear 30-31” tires without a fender trim), extended radius arms for ride quality, electric fan, electric power steering, and all the 2.9 mods I can cobble together (headers, MAF conversion, porting on heads and intake, free-floating rocker arms, etc). My ideas for the motor may change some after reading a bunch of stuff from @gaz and @PetroleumJunkie412 , but basically trying to build the thing to appear stockish but be upgraded for fuel efficiency and performance

 

[konrad911]

4.0 is low end TORQUE
HP for 4.0 and 2.9 are almost same...