When BMW NA boss fires up the BMW 3.0CSL for the Monterey historic-car races at Laguna Seca, he’ll be lighting off a new era for the car, which ran Sebring in 1975. The engine has just been rebuilt by Steve Dinan, whose V8 engines for the Team Ganassi prototypes have been winning long-distance events for the last few years.
That rebuilt was anything but simple. There are no parts for a 1975 factory M49 racing engine lying around, so other BMW engine parts had to be used instead of the original parts—and some parts had to made from scratch. “Pistons, connecting rods, and piston rings all had to be made by the suppliers who manufacture our usual racing-engine components,” says Dinan. “Rather than updating the design to modern technology, we tried to stay close to the original engine concept as possible.”
Such items as cam timing and fuel mixture had to be “guesstimated,” using Dinan’s experience at racing technology. The result? “The original engine was rated at 420 DIN horsepower at 8,250 rpm,” says Dinan. “On our dyno, we saw 443 SAE horsepower at 8,500. The difference between DIN and SAE is around 4%, or eighteen horsepower—so the actual difference was about five horsepower from its original build!”
In these days of turbocharged engines making lurid power, Dinan still admires the technology and challenge of getting power from normally aspirated engines. Of the legendary 3.0CSL six, he says, “It’s an impressive number for a 3.5-liter engine built in 1975!”—Satch Carlson
