Hi all Im new Here
I have a 1999 4.0 v8 I want to put a 1994 3.9 v8 in her what will I need to do?
Thank you very much in advance.

 

see your other post - oh, and if you have secondary air injection even more compatibility issues. The 99 uses the ECU to trigger spark, the 95 uses the distributor, I believe the cam position sensor is different, etc.

 

Yeah I was thinking the coils could just be changed I think I will look for a 1999 motor thanks

 

what if you installed the 94 as is only use a one wire distributor, it makes it a stand alone ignition system all you have to do is give it switched 12vt.

 

You would have to machine the block for the crankshaft sensor, then swap the cam, timing chain, and cover from a 4.0.

On top of that, the 4.0 has a precise ignition map compared to the 3.9. It would need a slightly different map given the different rod lengths of the 3.9 and 4.0

So you'd end up with an expensive swap that doesn't run as well as it should. I'd be surprised if there is more than 1 person on this planet that has done this. Find a 4.0

 

Thanks rob. I tour down my 4.0 thinking the block was trashed by the rod that came loose but it only cracked off the lower cylinder wall lip before the compression stroke so I think im good the rings don't even come close to the cracked lower part of the cylinder. I am going to test the water jackets though. Any input I would like to hear it.

 

Different rod length? The 3.9 and 4.0 are the same displacement, the 4.0 designation was adopted to differentiate between the 2 engines as the crank journal sizes were changed and the main caps were cross bolted in the 4.0. A late 3.9 isn't that hard to swap over. As long as it has the gear rotor pump in the timing cover it can be done. You would need to modify the block to accept a crank position sensor, install the appropriate timing components, and drill and tap for the knock sensors. You will need the 4.0 timing cover IIRC. Aside from these things you will need to use the flywheel and spacers off the 4.0.

 

yup, different rod length.

 

I suppose for the sake of argument you are correct in technical terms, they are longer.
Why is that supposed to matter? The rods are not interchangeable, the main and rod journals are approx 5mm larger on the 4.0. Both engines displace 3950cc, and both engines have the same bore and stroke. This is not as uncommon a conversion as you seem to think. How do you think Land Rover created the 4.0 in the first place?

 

I'm not sure what you are asking/arguing/talking about

rod length is different, piston TDC dwell is different, optimal ignition map is different.