Waiting for the next blizzard, I was pondering some snowy-day thoughts...

Namely, can the 2004 and later 4.2L V8s directly replace the earlier 4.0 engines? (presuming accessories and sensors swap over with no issues)

If my current engine should die at some point, it seems to me that it might make economic and reliability sense to swap in the latest engine long block that would fit and hook up. I'm not facing this now, but was curious.

 

By "earlier engines", do you mean the AJ26 or AJ27. The answer is different for each. AVOS, who used to hang around the XK8 forum, has done a pretty complete analysis of this issue.

 

Here are links to previous discussions on this subject. The answer is yes, but with limitations.

https://www.jaguarforums.com/forum/s...71&postcount=6

https://www.jaguarforums.com/forum/s...d.php?p=177881

 

The second reference by testpoint (thanks) says that you need to swap the engine front cover and the intake manifold. I wonder why?

I would think it would be easier to use the 4.2 accessories as they are, perhaps changing hoses or lines. And using the 4.2L intake manifold and throttle body, and adapting the air ducts. Or does the 4.2L intake stuff stick up so far it hits the hood/bonnet of the earlier body style?

 

The new engines have a different fuel injector which is apparently not compatible with the old ecu. The old fuel injectors apparently do not fit in the new manifolds. So, the assumption is that the easiest solution is to drill the new heads for the old manifold, or use the old heads. The thought crossed my mind to use the new ecu, but that seems like a really big deal for a bunch of reasons.. .

The issue on the front cover is apparently on;y applicable if you have VVTs, and has to do with the solenoid control and the oil pump. Since my interest is in SC engines, which do not have a VVT, I did not research that issue.

 

Following on from what Ross says, the induction set-up is different on the 4.2 it takes air from down the centre of the engine.
Also, blocks from Range Rover/Sport V8 S/C 4.4 can be used allegedly, with the same stuff off the 4.0 - same deal with supercharger on these blocks they need drilling but not a big job. Can you tell I'm thinking of doing one at some point.

 

How does the VVT on the AJ27 differ from the later engines? And I'm not sure I understand what the differences are in the oil sumps, that require switching over those parts. Would the later style bottom oil pan hit the X308 subframe or mounting areas?

 

My reference was from an AJ26 to the 4.2. The VVT changed from a two position control scheme to a proportional one. As to the oil pan, I suspect that is an issue of which car as much as any. I suspect the sump and pickup are a fairly minor issue, even if you had to fabricate or modify something. The reference to front cover has to do with the ouil pump. Andre Vos simply made the observation that since the later engine used proportional oil contol for the VVT, he believed the original oil pump should stay with the original VVT, I don't think it is necessarily a real concern.
If you have an AJ27, you are probably OK on most if not all of these issues.