Greetings!

I have recently acquired a 1976 XJS. I originally was talking to the previous owner since he was selling the motor (I was thinking about putting it in my xj6 project) and wanted to put a pontiac in it, but after some back and forth, I picked up the entire vehicle.

I haven't had a chance to go through the car as thoroughly as I would like but I do know that it isn't currently running (previous owner states it needs fuel pump and ballast resistor), has fairly minimal rust, and an interior that needs help, but is by no means dire.

I would like to build it into a decent performing GT car (mostly road going, occasional track use), reducing weight where I can without full on gutting it. Since this is a pre-HE engine, what are the best bang for the buck type modifications to breathe more life into the cat? I have read many theoretical possibilities with the motor, but I feel that 350-400hp would be decent start. Any advice would be greatly appreciated!

 

there is no "bang for the buck" KN CAI and headers options for an XJS. Opening the exhaust and letting it breath in helps some, but otherwise the engine itself needs to be changed in some way.

The VERY BEST thing you can do is get a manual transmission behind it. Let it breath and get it running like a top. to get 400hp you need to do something with the engine internals.

Your money will be best spend on a manual trans, changing the rear end gears and shedding weight. This engine ****ing loves to rev and has good low down torque. You are better off utilizing the engines power curve and getting rid of the mpg/mpg gears made for highway cruising. You will still get better mpg with a 5-6 speed anyway so its irrevlevant. Dropping weight to keep 300hp and have the same power to weight ratio as a 400hp 4000lb XJS is cheaper

 

Thanks for the info. I've been trying to hunt down some info on transmission swaps that don't cost a fortune, but beyond some references to putting together a more DIY transmission swap, but everything has been super light on details (and spending 5k+ isn't exactly what I had in mind). As for 400hp, sounds nice and all, but I think opening up the exhaust and intake are probably all I'll want for now. I'm not against tearing into the motor, but I'd rather prolong that if I can.

Otherwise, I've been going through the car, seeing what works, what doesn't, what I can remove, and budgeting accordingly.

First step is to get it mobile again.