2.9 and 4.0 Interchangeability

[Nez'sRanger]

Over the past couple months reading as much as I can on my 2.9 Ranger, I came across a few posts that mentioned parts that are interchangable on 2.9's and 4.0's like the starters and clutches. I know the 4.0 is in the same family as the 2.9, so my question is, how similar are the two? Are the heads something anyone's messed with swapping? I read about a cosworth 2.9 that had DOHC, I know the 4.0 had SOHC in 97... I wonder if it's possible to rig 97 4.0 heads up to a 2.9...
Just hoping to pick some more knowledgeable motorhead brains!
I love the idea of modding engines, and would like a bit more of a challenge than just putting in a 4.0!

 

[adsm08]

The 4.0 flywheel/clutch/starter is a nice upgrade for the 2.9.

The 4.0 SOHC started in 97 but was used until 2011 in a few different vehicles. You aren't going to be able to use those heads to turn the 2.9 into a SOHC engine, it just ain't gonna happen. There are block differences that will prevent you from installing the timing chain for the RH bank. Same for a 4.0 OHV. The 4.0 SOHC isn't a SOHC engine the way the 4.6 and 5.4 are where it was designed that way from day one. It was adapted from the older pushrod block, and so there is one chain from the crank to the "jack shaft" that goes in place of the cam on a pushrod engine. From there one chain comes off each end of the jack shaft, the front one going to the left head, the rear one going to the right head. The pushrod blocks have no place to run those two chains that go up to the cams.

4.0 OHV heads on a 2.9 would be a more realistic swap, but will lower compression due to the 4.0 having larger chambers. I'm not sure about the deck size though, and the 4.0 head may be longer or wider, or not. I've never had a set of each next to each other to compare.

You may be able to use a 4.0 crank to do a cheap DIY stroker kit, I'm really not sure.


The 2.9 DOHC heads and cams can be swapped onto a pushrod block from what I understand, but it was a Euro thing, and parts are hard to get.