Can any chime in and answer the question as to why the LR was fitted with the aj41 in n/a forn and the xk,xf were fitted with the aj34

On paper i know there isn't a huge difference in hp/torque however from a marketing point of view it would have been a huge positive as the later model xk100 essentially had the same 4.2 displacement as the xk150

 

Not sure the reasons behind it, apart from 4.4L being the capacity of the BMW M62 that was used in the L322 Range Rover before switching to a Jag engine.

There are a lot of minor differences between the AJ41 and the AJ34, the valve train is very different, the valves are longer in the AJ41 so different tappet arrangement, sump & oil-pickup different because of the front diff, the fuel management is also different (different fuel pump, no fuel pressure sensor used) probably quite a number of things not the same.

Why? Good question...

 

Cambo i just found it strange as to why they just didn't use the aj41 in jaguar

Prehaps the fact that jaguar's capacity would have been larger than Aston's v8 might have been one of those reasons

 

The 4.2L AJ33 existed before the 4.4L AJ41 in the Land Rover, or the 4.3L Aston version. It's not like the Jags were downsized, it was the other way round.