BMW M3 coupe stripped down to go club racing

BMW's M division is back in the business of building specialty street-legal race cars with a new lightweight version of the M3 called the GTS.

The lightweight coupe, set to go on sale in early 2010 at a yet-undisclosed price, was conceived as a limited-edition model primarily for club-based racing in much the same way that Porsche builds the 911 GT3 Clubsport.

But in a clear effort to link its track-based activities with the production-car side of its business, BMW's M division is offering the new car with a homologation package that will allow customers to register the M3 GTS for street use.

Helping to distinguish the new track-oriented M3 from the standard versions of the iconic two-door is a body kit based on the one used on BMW's 320si in the World Touring Car Championship. It includes a deeper front air dam with an integral splitter element and a large, adjustable, decklid-mounted rear wing. The traditional kidney grille and air vents in the front fenders get a dark finish.

BMW M division engineers gave the M3 GTS a carbon-fiber roof and removed much of the soundproofing material within the body to cut weight. The new car is claimed to weigh no more than 3,307 pounds--about 342 pounds less than its standard sibling.

Inside, there's a spartan interior. The standard trim is replaced by simple carbon-fiber and alcantara panels, while hard-shell front seats, six-point harnesses, a roll cage and a fire extinguisher are part of the race-grade package. Customers can also order the new BMW with a basic sound system and air conditioning.

At the heart of the M3 GTS is a heavily revised version of the M3's 4.0-liter V8. It has been increased in capacity by 10 percent, with a longer stroke extending the 90-degree unit out to 4.4 liters as part of efforts to provide the GTS with increased low-end performance while retaining the strong top-end attributes for which the standard engine is renowned.

Other changes include a larger carbon-fiber intake manifold, reworked throttle-body butterflies, a stiffer crankcase and revisions to the sump to provide more reliable oil scavenging at high cornering speeds. No specific output was revealed, but peak power is claimed to have increased by about 30 hp over the standard M3, taking it up to 450 hp and providing the M3 GTS with a power-to-weight ratio of 300 hp per ton.

The increased power is channeled through a beefed-up version of the M Division's seven-speed, dual-clutch Drivelogic transmission with remote shift paddles similar to those found on the standard M3. The Getrag-engineered unit is modified with ratios unique to the GTS, more resilient clutch plates and altered software mapping--all aimed at reducing shift times and providing even more aggressive action in manual mode.

The M3's electronic differential has been tweaked for greater lockup on overrun, while the dynamic stability control receives revised software mapping designed specifically for competition use.

Underneath, the M3's aluminum-intensive MacPherson strut (front) and multilink (rear) suspension were heavily revised with altered geometry and a rear sub-frame that bolts directly to the body. The shocks were reworked, with adjustment threads allowing adjustment of the compression and rebound characteristics. Unsprung masses have been reduced through the adoption of new 19-inch cast-aluminum competition wheels shod with 255/35ZR-19 (front) and 285/30ZR-19 (rear) Pirelli P-Zero Corsa tires.

Changes to the brakes see the single-piston floating caliper units used on the standard M3 replaced by new fixed calipers with six pistons up front and four pistons at the rear.

By Greg Kable