so i just bought a 04 xj8 for 1100 bucks in vegas with the 4.2l, 161k miles, I have ran compression test after a worsening number 7 cyl misfire and it was 80 psi, the number 5 is 145, rest are 160 so i would say thats a blown head gasket in between cylinders, i have a 4.0 from a 01 thats been in my garage for a year now with 97 k miles that i bought as a backup for my 07 rr hse, i would like to just dump that 4.0 into this 04 and be done with it, it looks like most people swap from 4.0 to 4.2, im worried about a warped cracked head, there is a reason why this motor blew the gasket id imagine, must have been low coolant overheated etc etc.

so my question is it appears many people have swapped from 4.0 to 4.2 but what about 4.2 to 4.0, i would guess it should be straight foward, i have read about the intake ports do not line up and something with vvt having to be swapped over and oil pump.

could i get away with just swapping the intake and porting to fit instead of tearing into the motor replacing cams etc etc.

 

Short answer is no.

 

yea i just got done trying to fit the 4.2 intake on the 4.0, not a chance, holes dont line up ports are way off, looks like its not going to work, i may have to try to salvage this 4.2.