I have a 99 xj8 4.0....I want to do more upgrades but dont know what my options are on this motor...I have a new intake setup with a custom exhaust but want more than that....please help!

 

Depends on your budget. Pouring money into a normally aspirated AJ26 really isn't economically prudent for the HP gains you may realize. After everything is said and done, you will find it would have been cheaper to buy a XJR for the amount of HP you get per dollar spent. To gain another 80 HP from a XJ8 you would have spend massive amounts of money, to stroke the motor, re-program the ECU and run headers and freer flowing cats. It's possible but not practical.

To make HP, there is not substitue for cubic inches or forced induction. You can always run the bottle for a short term gain but why??