When we last visited Dinan to test its supercharged M5, we noticed a black M3 sitting in one of the workshop bays with an experimental supercharger installation attached to its motor. It was not until nearly a year later that Dinan declared the S3-M3 engine project officially 49-state emissions legal and ready to roll, with California emissions certification just around the corner. The complete car with engine, chassis, and wheel and tire modifications is known as the Dinan S3-R M3.

From past experience, we can attest to the fact that Steve Dinan does not do things by half. He has built up his company slowly and steadily over the years, and today this organization has visibly more research, development, and testing resources than just about any other American tuner of European cars. Dinan makes a lot of its components in-house, where it can keep a very close eye on quality control. In fact, Dinan fabricates everything on this car on-site, apart from the springs, anti-roll bars, and brake components.

The basis of the Dinan conversion is a Vortech gear-driven supercharger, attached to the motor by CNC aluminum and steel mounting brackets for rigidity and precise drive-belt alignment. An automatic belt tensioner ensures consistent drive. A high-efficiency intercooler, high-flow cold-air intake system, 1.5mm larger-diameter throttle bodies, larger fuel-injectors, and free-flow exhaust are added.More power means more heat, and Dinan replaced the factory radiator with its plastic top and bottom tanks with a 35 percent larger capacity race-spec aluminum unit, as well as adding a larger oil cooler.

ECU recalibration for forced aspiration is not easy, since the program has to control not only fueling and ignition but also the drive-by-wire throttle, double VANOS, and a host of other functions. The software adjustments have been carried out to perfection, including losing the top speed limiter. The OBD II functions also work correctly with the new parameters, so no check lights come on and the factory diagnostic systems remain intact.

At 5.5 psi, boost pressure is relatively low and indeed has to be considering the high 11.5:1 compression ratio. Nonetheless, the gains are impressive. Power moves up from 333 bhp at 7900 rpm to 462 bhp at 8000 rpm and peak torque climbs from 262 lb-ft at 4900 rpm to 328 lb-ft at 5500 rpm.

The zero-to-60-mph time of 4.3 seconds and zero-to-100-mph in 10 flat are matched by a claimed 189 mph top speed, but as top speed is an autobahn thing, one component not normally changed by European tuners is the final drive. With relatively low speed limits in the United States, it is more important to go from zero to 100 mph very rapidly, and Dinan does a roaring trade in lower final drives. The only real downside is a fuel consumption of 17 mpg, since it is hard not to constantly dip into the rich powerband.

Replacing the stock 3.64:1 diff with Dinan's 3.91:1 limited-slip unit effectively delivers 7.4 percent more torque to the rear wheels, further enhancing acceleration both from a standing start and on the fly. Part of the ECU software reprogramming raises the rev limit slightly in the first two gears so that the car can reach 60 mph in second gear.

Exhaust notes are a subjective thing, and while some like the high frequency rasp and tizz of the factory M3 silencer, we prefer a deeper, more baritone straight-six soundtrack. In full battle cry, the Dinan sport exhaust has just such a deep voice. Overlaid by a slight whistle from the supercharger and the roaring fan attached to the intercooler core up front, this totally changes the aural character of the car to something more seriously weapons grade.

"We had many requests from customers for a new rear box to get rid of the tinny rasp the stock one makes under acceleration," Dinan tells us. "In flow testing, we quickly learned that the factory cross-flow design was a power loser. Our replacement unit sends the gases straight through two of the outlets, but since you could never sell an M3 exhaust without four big outlets, the second pair are dummies."

Dinan found that increasing the size of the front tires to 275/30-19, matched to the 285/30-19 tires at the rear, significantly reduces understeer. Consider this: The standard front rubber is 225/45-19, so there is now 50mm more rubber on the road at each front corner. In parenthesis, the rears go up by just 30mm per corner over stock, so the influence of the wider front rubber is significant, noticeably improving front-end bite and reducing the car's inherent understeer most evident in slow and medium speed bends when you are pushing hard.

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!