"Drive it like you stole it." Those may have been the five nicest words anyone's ever said to me. Whether they're the wisest words to say to someone who has just gotten behind the wheel of a twin-turbocharged, 3.9-liter, E34 M5 for the first time is debatable. Even so, I felt inclined.

Stepping onto the stiff clutch, comprised of a SPEC E46 M3 pressure plate and an M5 disc, and pushing and pulling through the heavy gearbox, the throws shortened with a Rogue shifter, the immediate impression is this is a man's car. As it's been stroked from 3.5 to 3.9 liters, there's plenty of torque down low to keep it drivable around town. The turbos are so seamlessly integrated to the powerband that it's impossible to tell when they start spooling. That is, until you really nail it.

But all hell doesn't necessarily break loose like with many turbocharged cars; instead, there's a relentless, linear surge of power all the way to its 7000-rpm redline. Huge swaths of terra firma are consumed through each gear while the rear tries to counter the weight transfer.

There seems to be no amount of wind resistance or weight liabilities that can stop it, even as the car begins to climb through the triple digits. And this is with the boost turned down to 9.5 psi during the break-in period.

The E34 is the forgotten M5. It didn't make quite the splash of its predecessor, the E28, or its successor, the E39. For a while, people didn't even know if BMW was going to bring it into the United States. And when they eventually did, only small numbers arrived. Spotting one on the road was about as likely as seeing Sasquatch riding a unicorn. Then came the 540i and its big V8, relegating the E34 M5 to near obsolescence.

The current owner, a die-hard BMW fan, has always admired the E34 for its understated design, and after he was tipped off that there was one for sale he jumped on it immediately. What makes this particular car unique is that the VIN number doesn't show up on BMW's database, leading to speculation that this may be one of a small batch of early, hand-built M5s never intended for sale to the public.

It's a Euro-spec model built in December 1991 that was imported and federalized by a German Air Force pilot stationed in New Mexico, but any history before that is still unknown. Shortly after buying the car, the owner blew a head gasket. He then took the car over to Jon Firpach at GoodSpeed Performance Lab in Scottsdale, Ariz., for repairs. He also wanted to put in a new chip and when they opened up the ECU, which was unlike the stock ECU, they found a few notes, written in German, wrapped in plastic and taped to the inside of the ECU box.

Firpach also noticed that the idle was particularly lopey, as if it had a hotter cam. This led to more speculation on the BMW forums that this car may also be one of the rumored 400-hp E34s that M Motorsport built strictly for in-house research. It is believed that those cars were painted the same diamond metallic color as this car here.

While looking over the engine, Firpach took some measurements for his own curiosity and realized that there was enough room for a turbo or two. He says he suggested a twin-turbo in jest, while the owner says Firpach tried to sell him on the idea of forced induction. Either way, a call to BMW engine guru Jim Row at Metric Mechanic was all it took for the owner to decide to go all-in. His only requirement was that engine not have any turbo lag.

Metric Mechanic already offered a 3.9-liter stroker program for the engine, which the owner originally intended to buy. Turbocharging it only required a redesign of the skirt on the forged pistons.

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