Hello,

My first post, and hello to everyone. I tried searching for this topic as I don’t want to contribute to redundant post, no luck. I’ve seen post about guys wanting to upgrade from a 3.9 to a 4.0 but nothing about anyone using a 3.9 in a 4.0........So here is my question::

I’ve been on the search for a ‘97 disco or just a GEM 4.0 to replace mine that has a slipped sleeve... no luck that makes any financial sense. Yesterday I came across a ‘94 defender 3.9 (not confirmed, haven’t looked at the vin yet) for $140 that according to the owner, he pulled because he changed everything to diesel, engine ran fine before being removed. I bought it with the thought of if it doesn’t work for my application, I’ll recoup my money easily.

Reading about it, it seems that the 3.9 doesn’t have a few sensors the. 4.0 does. If I were to go ahead and have the machine shop pull it apart and add these sensor areas (if possible) along with doing the crowned liners and trick items (Crowley cams, etc).... would this shoe into my disco or should I continue looking for a 4.0? Thanks in advance!

 

It will take some work to convert the electronic, but the 3.9 will bolt up no issue.

Defender, RRC or Disco 1 3.9 were all basically the same

 

You should be able to combine parts to make a good 4.0. Front cover and intake/plenum from the 4.0 with the 3.9 block.
*** Listen to Robert, he knows WAY more than me!!!

 

Theres no crank sensor hole or knock sensor mounts

the defender 3.9 will be serpentine belt so the crank key wont be long enough for the 4.0 cover

 

Way easier to take a 4.0L back to a 14CU configuration that it is to cut up a 3.9L block to accept a crank sensor and NOx sensors for GEMS. I would not recommend most people try this sort of thing. Maybe take it to a machine shop but I find it hard to believe a DI 4.0L is that hard to find real cheap.

 

I did it changing to carburator with a buick intake manifold.

 

If you're replacing sleeves in the 3.9, why wouldn't you just replace them in the 4.0 you have?