A couple questions, I have an 89 4.0ltr XJ. I have been given an 99 4.0 HO. I know there are things that wont transfer due to electronics, but I was wondering if the Cam would switch over.(99 cam into the 89 4.0) Both engines are stock and in good shape. Also "rebuilding" the 89 4.0 head (lap valves and new seals) was wondering what the specs were for the valve spring height. Mine are at 2.01".

On the 4.0 that you have your really only held back by the Renix fuel injection setup. I don't think that there would be a gainful advantage to swapping a stock cam for a stock cam. I do know that the intake manifold on the 99' will flow much better than the 89 if the throttle body will bolt up. Why not swap in the whole engine?

if you go that route of swapping in the new engine take both heads off the one off of the old engine and the one off of the new engine rebuild the old head and install it on the new(er) engine the reason i say this is because the new power tech 4.0 has a tendency to crack the head and the older one will remedy the problem bolt right on and give you a chace to pull a few more horses you know open the ports or just take a carbide sanding wheel and smooth down the intake ports and knock down all the high spots throttle body spacer will do wonders opt for the helical cut it smooths out airflow and devolps more intake vacuum, more intake vacuum means a more responsive engine and a few more horses another idea is to hook up a second electric cooling fan inplace of the engine driven cooling fan thats good for 8-12 horses on tap