From the BMW's the I've seen that people try to do forced induction it never turns out well unless you are willing to deal with problems and complications. If you are willing to put down around 10k to get this done and you really want more power you may want to consider selling the X5 and getting a earlier model Cayenne twin turbo. You will get similar power output with a stock engine. Then again, the Cayenne TT is not known to be reliable either. At least it will be easier to trouble shoot since you are dealing with a stock motor and you won't get killed by the resale of a SC X5.

If you're comfortable with the knowledge of how little resale value these things add, and are willing to go the extra mile for a quality tune, GO FOR IT. That twin screw is going to do so much more than the centrifugal that I'm locked into. Your six-speed auto will handle the torque gained on a pump gas setup. Man I wish I had a twin-screw for some real grunt off the line.

A well engineered long-term turbo or twin-turbo setup is all about packaging & underhood heat management. Long-term heating, interfering plumbing, greater number of parts & points for leaks, all should be considered. In this instance, it's an overly complex and arguably more expensive way of reaching the goal.

For what it's worth, I'm at 130k miles. 128k of them have been supercharged, and without a single failure where the supercharger was directly or the root cause of the fault. I blame it on system design and maintenance. If you pull the trigger on this, send me a PM regarding what engine/trans tune changes were made and how that was done.

Thank you everyone for your input and advice. Belknap as much as I'd like to go with your advice this is the family car so what I have decided to do is to buy an old model M3 (E46) and make it a project car, then I can do what I like to it and not have to worry about the family car blowing up on the freeway.

The overall feeling I get is that I am going to create a monster therefore might keep the X5 stock.

Thanks again
Andrew

Andrew, backup vehicle is always a good call. Good luck with your E46.

Here's some 6hp26 info, for what it's worth.