4.0L Swap Question

[BlackGT02]

OK.. I am not stranger to engines, engine swaps and getting greasy so I can handle the technical answer. My question is. If the 2.9L and 4.0L are both Cologne V6's why can't I just swap the intake and wiring from a 2.9 onto the 4.0? Or just the 4.0L short block into the BII? Why must you do the wiring and everything? Is there a difference in the head bolt pattern? Or does the speed density computer not know what to make of the 4.0L making the whole wiring swap necessary? What is the reasoning behing this? It seems to me you could just drop in the 4.0L long block, throw in the 2.9L intake and plug everything in. What gives?

 

[fastpakr]

The deck height on the 2.9 is shorter than the 4.0, so the heads/intake swap won't work. The speed density computer cannot compensate for a change that extreme. If you wanted to use a 2.9 MAF system (CA '90+ only) that might be possible, but that requires some swapping in and of itself and I'm not really sure how you'd handle the ignition system. By then it would be easier to just do the whole wiring swap.

 

[BlackBII]

What he said. Intake/Head differences, cannot swap between the two.

2.9's ecu wouldn't be able to get the 4.0 running correctly. The entire swap is just easier.

 

[BlackGT02]

Nuff said.. I can understand that language. Speed density is great for power, bad for adaptation. I would really like to do this swap but I have a good running 2.9L in my donor BII right now so I will just put it in for now and maybe plan on the 4.0L down the road some time. Thanks..