Dinan S2-M3

Dinan S2-M3 Dinan S2-M3
Specialty File

Why would anyone acquire a car that already had been thoroughly modified by one of the best performance-car companies in the world and then modify it again? That's the question we asked Steve Dinan, the well-known American tuner, when he came by our sweatshop and dropped off his latest car, a modified BMW M3 he's dubbed the S2-M3.

Simple, says he: "Folks who want to go fast start with the fastest car they can get and then come to me to make it go even faster." For BMW fans, the quickest model is the $48,195 333-hp M3, a legendary car that's always on our 10Best list. It's so good that in 1997 we named it the Best-Handling Car, period—money no object.

It's hard to imagine anyone even trying to improve on the M3, but Dinan says his $17,798 package of engine and suspension mods does indeed do just that. This is not a new experience for us. We had the same doubts last year when he dropped off a reworked M5, but sure enough, we did like it better than the stock car.

Dinan acknowledges the inherent dangers of such ventures and is well aware that in stock trim the M3's 333-hp, 3.2-liter six-cylinder engine, for example, is already highly tuned, and there aren't a lot of inexpensive things he can do to significantly increase horsepower. That's why the list of new power parts has just three items on it: an airbox, an airflow meter, and a muffler.

The airbox is larger than the stock unit and also has a snorkel that inhales cold air from the area between the top of the front grille and the hood. In addition to the less restrictive airflow meter, the package includes the relocation of the intake-air-temperature sensor so it's closer to the six throttle bodies, a move Dinan says provides the engine computer with more accurate intake-air-temperature readings. The throttle bodies are also bored out for further airflow increases.

The only change to the exhaust system is the muffler. The standard M3 uses a muffler that has two outlets, so from the rear of the car there are two pairs of exhaust pipes sticking out. Dinan's muffler uses only one larger, smoother outlet because he says more air is able to flow out. A dummy pair of exhaust tips retains the stock look.

Finally, Dinan reprograms the M3's engine computer, which controls a great many engine functions, including the intake- and exhaust-valve timing, spark timing, fuel flow, and throttles. In addition to adapting those engine parameters to the new parts, Dinan increased the rev limit by 200 rpm to 8200 and also removed the top-speed governor. We don't top-speed-test modified cars, but Dinan says the S2-M3 is good for 189 mph.

All the modifications added a claimed 28 horses to the power bank, an 8.4-percent improvement. That's not enough for a customer to sense a thrilling boost in power, so as part of the package, Dinan also puts in a shorter final-drive ratio (3.91:1 versus 3.62:1) to make for sprightlier sprints. It is also interesting to note that thanks to the higher rev limit Dinan's car clears 60 mph in second gear, the same as the stock car.

Dinan feels the greatest improvement he's made over the stock M3 is in the suspension department. As we do, he thinks the M3 is too stiff, but he goes even further, contending that the handling benefits don't justify that hard ride. So the S2-M3 package includes new 12-position adjustable shocks and anti-roll bars, stiffer springs, front camber plates, front and rear strut-tower braces, and larger wheels and tires. Dinan claims his car rides about as well—or not—as the stocker but has a lot more grip. Its 0.96-g skidpad figure is a bunch more than a stock M3's. We've tested three stockers, and the numbers have ranged from 0.84 to 0.87.

We did not see that much of an improvement during the acceleration tests. The S2-M3 zips to 60 mph in only 4.6 seconds, but we've tested a stocker that hit 60 in 4.5. Similarly, the S2-M3 cleared the quarter in 13.2 seconds at 107 mph, and that quick stocker did it in 13.1 at 107. It's worth noting that we've also tested an M3 that needed 4.8 seconds to reach 60 mph and 13.6 seconds to hit the quarter at 105 mph.

Dinan did, however, improve the handling. There's a crispness in the S2-M3 that adds a wonderful liveliness to the driving experience. It's sort of a strange thing, because if you drive an M3, you think it handles pretty well and there aren't really any faults. But then you drive the Dinan car, and it's as if someone had turned on the lights.

Especially noticeable was the turn-in response. The S2-M3 rips through turns with an easy controllability and seemingly limitless grip. We didn't tinker with the adjustable shocks (ours were set with the front slightly stiffer than the rear), but Dinan says there's a large range of adjustability that allows owners to fine-tune the handling for precisely the balance desired. The Dinan car isn't necessarily faster at the drag strip, but on a racetrack, where the extra grip and handling would come into play, it would leave the stocker for dead.

If you don't have the cash for the entire S2-M3 package, all the parts—which are covered by a warranty that matches BMW's new-car one—are available à la carte at one of the 120 BMW dealers that carry and install Dinan parts.

Dinan, 865 Jarvis Drive, Morgan Hill, California 95037; 408-779-8584; www.dinanbmw.com.