I have a Jet chip. All I can say about it is that it gives me better throttle response. As Doc says - no noticeable difference in HP or torque. If you are looking for cheapest $/HP then you need to look at forced injection. Case in point - the supercharger I installed in my other car gave me 57% increase in HP and a 43%increase in torque. In terms of $/HP it was $48 / HP - now that is real value that you can feel in the seat of your pants. I have looked and looked for either a turbo kit or supercharger kit for the XK - lots of Mopar stuff but no one that has tuned one of these to our ECU's. You can be adventurous and try it yourself OR you can try and get a tuner to do it for you. If I had to guess - and this is just a guess - I would say after the Jet chip, CAI and cat back I might have eeked out 15-20 hp - pretty expensive ponies....