When someone says "sports car," I generally think small, lightweight, sparsely equipped and slightly juvenile. Likewise, when I hear "GT," I think: quick but not fast, comfort over maximum performance-and dare I say-slightly boring. Steve Dinan has never been one for convention. Equal parts mad scientist and hot rodder in his DNA have led him to build cars that aren't defined by general rules. Sometimes it seems as though they aren't even encumbered by the basic laws of Newtonian physics.

A BMW M6 is at the sportier end of the GT category, but with world-class luxury and handling more appropriate for back road touring than carving up the race track, there aren't many enthusiasts that would call it a true sports car.

To get world-class acceleration numbers out of a 3,900-pound car requires some serious grunt. From the M assembly line the M6 is equipped with a high-strung, 5.0-liter, 500hp V10. Pretty impressive, but with this thing's considerable mass the relatively diminutive 383 lb-ft of torque-peaking at a lofty 6100 rpm-just isn't that much. The stock M6 is quick, but not world-class sports-car fast. Which brings us back to Steve Dinan.

Dinan wasn't interested in forced-induction solutions to this particular problem. He wanted to retain all the feel of the naturally aspirated engine, with its individual throttle bodies for each cylinder, and celebrate the looming end of the second era of big-displacement power the right way. Using his years of experience gained building and racing Daytona prototypes, a plan for stroking and boring the V10 was put in motion.

The crankshaft is a one-piece billet work of metallurgical art. It's possible that a welded crank may have sufficed, but the thought of a welded crank spinning over 8000 rpm gives us all a cold shiver. Pistons are sourced from the O.E. supplier, Mahle. Measuring 93mm, these forged units combine with the 83mm stroker crank to bring the engine to 5.7 liters of displacement. That's 350 cubic inches to you hot-rodders. The block is bored in-house at Dinan's Morgan Hill, Calif., facility, and special care has to be taken to ensure the aluminum-silicon alloy is properly finished for maximum effect. A final honing technique must be used that removes a very specific amount of the aluminum and leaves the dispersed silicon still in place to create a silicon cylinder lining. Connecting the spinning and reciprocating mass are Dinan's proprietary lightweight connecting rods. The whole assembly is blueprinted, balanced, and assigned a Dinan serial number before being installed in a car.

From behind the wheel, the bigger V10 is incredible. The engine sings with a mechanical smoothness akin to a 628hp sewing machine. The power is smooth and gains steadily, there are no dead spots in the curve and it doesn't punish you for coming out of a turn in too low a gear like the factory V10. It revs with the eagerness of a sportbike and even sounds like one as it goes flying by. There's no harshness-even bouncing it off the rev-limiter in first gear it feels like it could probably spin to ten grand if it had the cam to breathe that high.

My first experience driving it involved laying down two smoking black strips using launch control and flashing through first gear faster than I could comprehend. As fast as the car is, it doesn't have the violent feeling usually associated with a powerplant of this magnitude. Power is smooth and delivered completely from normal aspiration. With their enlarged individual throttle bodies, each piston is doing equal work all the time. The current fuel market the way it is, big engines like this may seem politically incorrect. They are inefficient, loud, brutish even, but the experience makes you wonder... if we could turn the moon into gasoline, would we really miss the tides that much?

As you may expect, as much, if not more, attention went into chassis development. The factory-spec M6 is a decent handling car, but never feels as though it really wants to attack corners. It pulls an impressive g and will change direction quickly enough, but understeer and a lack of that knife-edge precision expected from a real sports car seems to elude the bigger BMWs. Springs, a rear sway bar, and various other bits combine to give Dinan's S3 M6 a lowered ride and fight roll with more success. There are a few more interesting things going on here, however. First, geometry changes in front add the steering feel normally missing. Notable among the improvements is slightly more caster. Not only does it add a more precise on-center feel, it adds just enough resistance from trail and weight jacking to make turn-in feel racecar precise.

The second point of interest in the Dinan car is how the problem of severely limited stock suspension travel was dealt with. BMW had to keep its shock towers extremely low to maximize trunk space. The result is limited travel in back and a rather rough ride. Dinan re-engineered the rear spring perches to maximize travel and designed custom bump stops that work in conjunction with the extra stroke. The result is a car with an inch lower ride height, more suspension travel, and the factory's electronically adjustable shocks still fully functional.

The S3's dynamics are aggressive yet still at least as comfortable as stock, maybe more so. Driving it isn't a battle with the front wheels as with the stock car. It's very neutral and easy to rotate. It also puts power down surprisingly well, thanks in part to bigger contact patches at the rear, but also due to the chassis not immediately squatting down onto the bump stops. In the first three gears, there's plenty of torque to swing the back end around at will. In faster corners, the car remains thankfully well behaved and doesn't feel like it wants to swap ends, even hard on the throttle. Again, it's the smooth power delivery of a big displacement engine coupled with a well-sorted chassis. Dial in steering and throttle inputs smoothly and the car rewards with fast, clean cornering. Flick-and-stomp results in some seriously fun drifting. You could go through a pair of rear tires in one afternoon of hoonage, but it might just be worth it.

So what does something like a Dinan S3 cost? The final price on the entire conversion hasn't been announced yet. The engine package alone is roughly 40 grand, but this is for essentially a race engine with a full four-year/ 50,000-mile warranty. Simply chipping your stock BMW will have the dealership tearing up your warranty papers and showing you the door. Dinan's warranty has to justify at least a quarter of the asking price.

Options on the car we tested included a free-flow intake system that uses two high-capacity cone filters encased in two separate airboxes with beautiful and functional carbon-fiber lids. They also include larger air-mass sensors with relocated air temperature sensors for accurate metering. On the other end was a Dinan exhaust system composed of a middle section designed for higher flow rates and rear mufflers with Dinan-designed "cool-tips" that pull in a small amount of outside air just at the tips to keep temperatures down and avoid discoloration. Inside the car, the new exhaust note is hardly perceptible. At wide-open throttle, the exhaust sounds like the world's meanest sport bike. It wails with a deep undertone that lets you know you aren't dealing with some 3.0-liter screamer.

Exterior modifications are left to a minimum. Dinan lightweight 19-inch wheels look the part, but more importantly shave a total of 32 pounds off the rotating and unsprung weight. Combine that with a few more pounds off each corner from the Brembo-built brakes and you have a drop in mass that really makes a big difference in performance.

A conversion like this is as high-dollar as it is high-performance. It isn't for everyone, but for people with the means, nothing else is going to feel or sound like the Dinan S3 M6. You aren't just buying an upgrade kit. You're building a monument to displacement. Fire it up, smoke the tires and give big engines the send-off they deserve.

Dinan S3 M6
Longitudinal front engine, rear-wheel drive

5.7-liter V10, dohc, 40-valve.Dinan forged one-piece crankshaft, forged pistons, connecting rods, high-flow intakes and air mass meters, 13-percent underdrive pulley, center- and rear-section free-flow exhaust, enlarged individual throttle bodies, Dinan software

Seven-speed SMG

Factory EDC supplemented with Dinan springs, rear anti-roll bar, bump stops, rear spring perches, front adjustable mono-balls (both caster and camber), front lower A-arm spherical bearings, carbon-fiber chassis braces

Brembo-built assemblies, six-piston monoblock calipers with 15-inch two-piece rotors (f), four-piston aluminum calipers with 15-inch two-piece rotors

*Wheels and Tires
Dinan, 9x19 (f), 10x19 (r)Michelin Pilot Sport 2, 275/35 (f), 305/30 (r)

Peak Power: 628 hp @ 7500 rpmPeak Torque: 480 lb-ft @6000rpm0-60 mph: 4.1 secTop Speed: 203 mph*Dinan data


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