Cain bought this car in 2000, a few years after first seeing it at the Monterey Historics. At that point, the car had been restored by Art Simonds, known in BMW circles for his work on CSLs and TISAs. Cain said he bought this US-spec 2002 originally for the bodywork. Simmons had done a masterful job and Cain was well aware of how much time and effort it would take to bring another car up to this level.
The plan was relatively straightforward: use all BMW parts, minimize weight and maximize power while building a car with 50/50 weight distribution. Sounds easy enough. Apparently, Cain isn't happy unless he has a challenge. Perfectly balanced weight distribution moved from being a guideline to an obsession. He was thinking rear-mounted transmission. A transaxle was never considered, Cain wanted to stick with an OE Getrag gearbox. It was moved to the rear, roughly six inches in front of the E39 differential housing that contains a Quaife limited-slip diff. It sits in a stock subframe modified with E28 and E3 components. Obviously, the rear floor was seriously reworked. There's even a viewing port for people who don't believe the transmission is in back.
To maximize power, it was decided nothing short of six cylinders would suffice. An eBay search turned up a 1000-mile 3.0-liter M54 engine from a totaled X5. With the new powerplant being significantly longer and heavier than the outgoing unit, it would have to be repositioned in accordance with weight distribution philosophy. The firewall was cut and the engine sits with roughly a full two cylinders of length protruding into the cabin. A pseudo torque tube set-up was custom fabricated to connect the clutch to the transmission in its new rearward position. Again, the firewall and floor were reworked and anyone unfamiliar with 2002s would never know it didn't leave the factory this way.
While a stock M54 engine is decent enough, it doesn't put out the kind of power Cain was looking for. Forced induction was the only answer. Wanting to run stock compression, a low-boost system was the way to go. He wanted fast spool-up, so twin turbos were chosen over a larger single unit. Factory exhaust manifolds were modified to bolt up to two KKK hybrid K14/K16 turbos. Once past the turbos, exhaust gases exit through two separate rear-mounted titanium mufflers. A single Tial wastegate sits on top, servicing both turbos.
Intake air first passes through a low-mounted BMW airbox that breathes cool air from the front of the car. After getting squeezed into action through the turbos, air is directed through the front-mounted intercooler, regulated by a cable-operated throttle body (sourced from a 3.0-liter V8), then treated to a custom-fabricated carbon fiber plenum that looks like it came straight from BMW Motorsports. Cain (and brother, Joe) first shaped the plenum out of surfboard foam, then used tooling grade carbon fiber in a wet lay-up around the male mold. The result is amazing and is even finished with a mocked-up BMW component ID sticker.
Cain soon realized he was not going to get the desired results with factory injection. After looking at several aftermarket set-ups, Autronic was considered the best option. It can control every aspect of the engine, including VANOS. It also utilizes all factory sensors and controls the factory ignition coils.
Dyno tuning was handled by Ben Strader at EFI University in Temecula, California. The car currently runs on pump gas and so is limited to 7psi, which is still considerable given the factory 10.5:1 compression ratio. It puts down 335 wheel-hp, but further tuning will surely net more power.