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the Roundel Feature Article ISR -- Dinan's M Roadster Two years ago we got word of an interesting project, hush-hush, top secret, a casual comment dropped by an unsuspecting BMW NA minion in an unguarded moment: supercharged M roadster. This was while the world was still impressed with the ordinary M roadster -- an interesting concept, that "ordinary M roadster" -- although one or two had been fitted with blowers by private shops. But this one was different. For one thing, it was being set up by Dinan Engineering on the California coast. For another, it was the personal project of Vic Doolan -- then president of BMW NA.
Tides and fortunes change, interest wanes. Doolan went to Ford, the BMW public started for the new M3, the new M3, and the unobtainable Z8. The M roadster -- even a hotrod version -- was old news. Nobody even seems to know what happened to Doolan's steroid toy. But what if you could get your hands on such a car? Not as a one-off special, not as a design exercise by a demented speed merchant, not as a shade-tree hack job by your cousin Zeke who put the Corvette engine in the Jeep and forgot about the brakes -- what if you could just plunk down the cash to buy everything puts into a car -- coupled with everything Steve Dinan knows about building a car? Dinan's been building fast cars for years, of course -- when he opened his BMW tuning shop back in 1979, on of his goals was to manufacture hi own special BMW -- and the Doolan roadster was simply another interesting engineering challenge to the team that was routinely getting over 600 horsepower our of twin-turbo 850 coupes. The company made big news a few years ago when BMW allowed their dealers to sell and service Dinan-modified BMW's, an agreement made possible because Dinan was willing to match the factory warranty on certain modifications and provide their own extensive coverage on more complicated upgrades such as superchargers. The venture has been satisfactory: there are now 81 BMW/Dinan dealers in the U.S., with a new one added every month. But the increased demand for Dinan equipment -- along with an underlying desire for more
power-brought additional complications.
By late 998 a Dinan supercharger kit for the
M roadster pumped the little rocket up to 340
horsepower-but that wasn't completely satisfactory.
"People think of me as a horsepower
guy," Dinan has said, "but I'm really more interested
in handling." It's easy enough to make
horsepower these days, but where do you put it?
Suspension design and modification, brakes,
computer remapping-all the minute details that
go into building factory prototypes are usually
beyond the reach of the individual enthusiast.
Even the authorized Dinan dealers, BMW
franchises licensed to carry and install Dinan
performance parts, have their limits. "It's
complicated," says Dinan, "because of the level
of modification. Every system is affected.
"The factory works program came about from our desire to build more cars with intercooled, blown power," he adds. "The increased power puts enough additional stress on the car that many systems needed to be re-engineered. We felt that it wasn't possible for the independent technician to install the product and have it come out right; in order to have control over the outcome of the total vehicle, we need to build it ourselves." It was time to bring the car inside. "Everybody has his own ideas about what a car should be," says Dinan. "This time I wanted to build car the way I want to build a car." But that meant he had to step into the complex role of Factory Works Builder-a manufacturer-the only BMW tuner with that status in the U.S. and one of only a few in the world. While there have been other noted U.S. tuners like T.C. Kline, Ray Korman, and Turner Motorsport, Dinan's volume and manufacturer status puts his company on the same plane with Alpina, Hartge, and AC Schnitzer in Gemany -- companies that have virtually no presence in the States. That role-a whole new level of commitment and responsibility-was debated within the Mountain View company for months. The concept was intriguing; for years, certain fast BMWs have had chrome "Dinan" badges on their flanks; what if, for a few certain customers, for a few certain cars, this meant that the cars came to Mountain View to be hand-built as signature Dinan-edition rides? Modified, rebuilt, and hand-crafted as individual examples of the ultimate tuner's art? "Well," laughs Dinan, "We still don't know if we can sell any." The aim is to sell exactly fifty: fifty M roadsters. Fifty M5s. And fifty new M3s. "Actually," laughs Dinan, "the number plates have space for two digits-so I guess we could sell up to 99!" In addition to the space for the numbers, there's room on that plate for two signatures: Steve Dinan's and that of the individual responsible for building that particular car. The prototype -- dubbed the ISR3 for "Intercooled Super- charged Roadster, 3 Series" -- is signed by Matt Taylor. (These new works cars will not be sold on the showroom floor, of course; to get one, you special-order the car from a Dinan dealer, who then ships it to Dinan's shop for production.) So what has Taylor the Builder wrought? That's where the fun begins; instead of selling a kit limited to this or a few parts to a6hieve that, now the plan was to simply build the ultimate Dinan. The ISR3 is a case in point; the original Dinan Stage 2 Supercharger System cranked out 340 ponies to boot a roadster to 60 mph in 4.8 seconds. You can't add another 50 or 60 without proper modification of brakes, suspension, and drivetrain. There's no such thing as too much power in Steve Dinan's philosophy, but everything else has to match it -- and if it's your name on the trunk, you have to have some control over the construction.
Making more power was likely the easiest task: A huge intercooler found its way into the intake, and supercharger boost pressure was bumped up to produce nearly 400 horsepower. An engine-oil cooler keeps the innards cool. A lightweight clutch assembly with a 20% higher clamp load sits on an aluminum flywheel for improved throttle response. The electric radiator fan is coupled to the intercooler. Describing the drivetrain modifications, Dinan's PR guys border on irony: "The combination of a short wheelbase," they write, "roadster chassis flex, and the rapid camber and toe-angle changes associated with the stock trail ing-arm suspension system, produce handling that some have described as `twitchy'....Ha! Many automotive journalists--some who can actually drive--have commented on the tail end of the M and its roadster sibs, and they use "twitchy" when they're being kind. "Bunny hop" is one commonly-heard term for the Z3, and "scary" is heard from those who do not understand that the M roadster must be taken firmly in hand--and foot. Since Dinan was upping the ante by over 150 horses, serious thought had to be given to handling. Special springs were bent, Koni/Dinan shocks were specially valved, and 22mm anti-roll bars were fastened fore and aft. Camber, caster, and toe are tweaked to create suspension geometry with no surprises. The car has also been fitted with larger wheels and tires, 17x8.5" (255/40-17) in front and 17x9.5" (285/40-17) in back. Those rear boots straddle a lower-ratio differential to reinstate the acceleration stolen by the taller tires; when everything's tight and the paint is dry, the acceleration is moderately stunning-that 60 mph time is now down to 4.6, and the car cranks through a quarter in a tick over thirteen seconds at over 105--but the real test will be what the car does when you carry that speed through the twisties, or how long you can depend on its reliability, or how civilized the whole package is over the long haul. Fifty people will have a chance to find out. Engine: intercooled supercharged straight six; Vortech helical-cut-gear-driven supercharger for quiet reliability; 10 pounds boost into 10.5:1 compression; 50-state emissions legal. Two different sized compressor bypass valves, one before and one after the intercooler to eliminate low-speed stumble and surging typical with "high boost" aftermarket supercharger systems. Thermostatically controlled engine oil cooler, enhanced fuel delivery system with larger high-flow fuel injectors. Air filter located outside engine compartment to insure exposure to cool, dense air. Integrated bumper ducting provides ram air effect as road speed increases. High Flow Throttle Body: Internal diameter of throttle body has been increased for improved intake airflow. Throttle response is also faster as a result of the modified shape. High-Flow Air Flow Meter: A larger-diameter air-flow meter is included in order to improve Intake airflow efficiency. The design incorporates a unique "labyrinth" for improved air-flow-meter-voltage stability as well as shielding it from cylinder pulses for a smooth idle and improved peak horsepower. High Flow Intake Manifold: Polished and ported with larger-diameter intake runners for maximum intake efficiency and resulting power gains. Engine Management System: The Siemens engine-manage ment system has been programmed for maximum power gains, driveability, and emissions compliance. System maintains all "On Board Diagnostic" (OBD II) functions and ignition timing and air/fuel mixtures are optimal throughout the engine's operating range. VANOS (variable cam timing system) has been reprogrammed for maximum power gains throughout the engine's operating range. Free Flow Exhaust: Stainless steel, free-flow mufflers insure that backpressure is kept to a minimum, without creating an unacceptable exhaust note. Clutch: Stock "dual mass" flywheel and clutch assembly replaced with Dinan Stage 2 Clutch Assembly. Lightweight aluminum flywheel reduces clutch weight by nearly 15 Ibs. or 39%. Clutch clamp pressure increased by 20%. 3.38:1 Limited-Slip Differential: Final-drive gearing has been lowered from stock 3.23:1 ratio to compensate for the increased outer diameter of 285/40-17 tires in the rear. Performance Springs: Increased spring rates and a modestly lower ride height provide greater control and traction in turns. Koni/Dinan Externally Adjustable Struts and Shocks: Matched with Dinan springs for maximum control. Features custom digressive compression valving for more low-speed shock shaft velocity control, providing greater restriction of camber and toe-angle changes. Front struts are externally adjustable for personalized control of ride quality and handling characteristics Anti-roll Bars: 22mm front and rear adjustable anti roll bars Front Camber Plates: Relocate strut pick-up points for two degrees negative camber in the front, greatly improving turn-in, Camber Adjustable Rear Subframe: Provides adjustment of camber angles at the rear of the car. Front Strut Tower Brace: Reduces flex at the shock towers for sharper handling. Wheels and Tires: Front: 1 7x8.5" Dinan Three-piece modular wheels, 255/40-17 Michelin Pilot Sport tires. Rear: 1 7x9.5" Dinan Three-piece modular wheels, 285/40-17 Michelin Pilot Sport tires. Brakes: Brake pads replaced with carbon/metallic pads. Warranty: The lSR3 is guaranteed for the period matching the remainder of the original vehicle manufacturer's warranty up to four years or 50,000 miles, whichever comes first. Dinan's warranty covers the entire lSR3 conversion, as well as any affected factory drivetrain components, through the term of the original vehicle manufacturer's new-car warranty period. If the vehicle is no longer covered by the original vehicle manufac- turer's warranty, the conversion is guaranteed fora period of two years with no limit on mileage. Emissions Tests and Status: The lSR3 has passed all applicable laboratory emissions testing for 50 state emissions legal status.
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