As many of you know, I bought my E39 540i from Bimmerwerkz.com user Eric S. back about seven months ago. It had 130,000 miles on it and had been very well-maintained, with many very tasteful upgrades, all of which I would have done myself anyway. Since then, the car has become a Dinan 5 with further suspension work, a Dinan free-flowing cat-back exhaust, and software. I previously drove an E36 M3, and while I was very impressed with the 540's greater torque and horsepower numbers, I knew somewhere down deep that I would eventually want to go F/I--and sooner rather than later.
After a lot of thought and budget-calculating, I settled on the VF Engineering supercharger kit. The numbers for the kit from the VF dynos are 415 horsepower and 400 ft-lbs of torque at 6psi. That is running on 91 octane California gas and with the stock exhaust system. Given that I always run on 93 octane and have a free-flowing exhaust, I would imagine that my numbers are now a tad higher than that. For comparison's sake, the numbers for a stock E39 M5 are 394 hp and 369 ft-lbs of torque.
Before, I drove a highway beast. Drop it into 3rd gear at 55 mph, and I practically ruled the road.
Now, I drive a highway monster. Huge gobs of power are available in every gear. Changing gears when I'm really going for it means that the car takes a HUGE lunge forward when the clutch engages. The exhaust sounded great before. Now it sounds deeper, bassier, meaner at low RPM, and at high RPM, it practically sings. I haven't taken it to a track or dynoed it yet, but I have every confidence that I'll be quite satisfied with the results when I do.
What is most impressive to me is the smoothness of the results. The E39 540, despite its huge amounts of stock torque, accelerates more smoothly than any other car I'd owned due to the rail-flat torque curve. The supercharged version has a much steeper torque curve...but it is equally flat. It presses me firmly back into my seat when I give it the beans, no question. If it was the ultimate driving machine before, I can't even think of adjectives to describe it now.
Kit cost from VF: I paid $6,000, but I hear there's a group buy going on now over at bimmerforums so you can get it for less.
VF recommends 10-11 hours of labour.
I have an obsessive-compulsive mechanic who makes everything look OEM and act flawlessly, so I got charged 25 hours of labour. (And given the quality of Ron's work, I don't begrudge him a minute of it.)
Needless to say, I'm on cloud nine right now.