It was a couple of years ago, but whilst studing for my degree, me and a friend had a pissed up idea to put a VR6 in a Mk2 and supercharged it. It was DAMN quick. But didn't handle, even though we spent a fortune on the suspension......... anyway i digress.
We tried using the rather obvious choice of superchips, which were fine for the type of things you are probably after, (Standard engine?). But we found that because of the stupid amounts of power the thing could produce, we went for a complete Lumenition management system with trottle bodies, injectors, the lot funded, rather kindly, by the University. (Nice!).
These are damn expensive, (at the time it was around ?3500) but were brilliant. you could map every thing from a laptop, and spend hours, if not years messing around with every conceiveable aspect of fuelling and ignition timing. Hell we got the thing up to 296BHP on the test bed before we fitted it to the Mk2, It could have taken more, but considering if we blew it, we had to get a new one with our own cash, decided against it. so we down tuned it to a nice round 220 for the road. Happy days.
Anyway sorry about that. yeah, try superchips.