Hartge took the M5 V8 engine and placed it into the E46 3-Series. 

The Hartge H50 is a front-engine, rear-wheel-drive, 5-passenger, 2-door sedan with an M5 engine. Other modifications include a higher rev limit and a reprogrammed ECU.

You start with an E46 sedan and an M5 engine. You take out the E46 engine and you put in the M5 engine. Simple? Well, the M5's V-8 and six-speed manual transmission is no longer than the original six, so the fire wall remains untouched, but it is much wider. It is so much wider that the steering column had to be routed through the left exhaust header spaghetti, and the oil circulation must pass through the left engine mount.

How strong is it? Car and Driver reports that the H50 smokes the rear tires if you drop the clutch with any kind of revs on the dial. Here's what they said:

To hook it up, we had to let in the clutch at little more than idle speed, and even then the car would still smoke the fat 265/30ZR-19 Pirelli P7000s if we went abruptly to full throttle. Then, if we shifted out of first gear too exuberantly, the tires would spin well into second. All this with a fairly decent weight distribution of 53 percent up front and 47 percent in the rear.

Are you getting the picture here? This car is strong—nearly 400 hp strong—and it has tons of torque available across the engine's range. On the Streets course, this translates into telescoped straights, where you find yourself threshold-braking even when you weren't planning to, just to get slowed down for the bends.

On the exit of those bends, any overenthusiasm on the part of your right foot will push this car into power oversteer. Yeahhh, baby! But it's not like the car is way loose or anything. On the contrary, it's set up tautly, with lowered and stiffened springs, firm shocks, and beefy bars, and it will understeer at the limit as its maker intended until you get on the loud pedal. 

HARTGE Official Website has all the info, including options and accessories.

Car and Driver review. They put the Hartge H50 through a series of tests at Willow Springs race track.

Birds from the UK has all the info about the H50, including a pdf file you can download. They have info on exhausts, brakes, wheels, styling, accessories, and a pricelist.

Fast Autos has pictures and some info.

Tuning Project website in French.