When you drive fast cars for a living, it's difficult not to be blasé when a tuner claims that his latest car is the best thing since sliced bread. But when a car sets your pulse racing just like it did when you were a newbie, you know you're on to something special.That happened when I drove Nowack's 5.7-liter M5. The claimed 628 hp and 457 lb-ft of torque are impressive enough, but this engine really can set the hair on the back of your neck tingling.

The enlarged V10 starts with a deeper, angrier bark. Blip the throttle and you can feel the engine rock on its mounts, the distinctive offbeat V10 howling before it settles into a steady, grumbling idle that threatens imminent thunder and lightning.

At town speeds it's as docile as you could wish for. In fact, it's better than standard since the beefier torque curve confers a "waftability" to its low-speed behavior. While on the one hand it responds more crisply, and revs even higher than stock at the top end, the more under-square dimensions help its newfound torque-rich character deliver a creamy smoothness of delivery that catches you unawares.

Top-end performance is awesome. It punches hard through the gears, and that uncorked V10 wail gives it the keen soundtrack of a Lamborghini Gallardo. It's this, and the way it pulls with renewed vigor between 7000 and 8200 rpm in fourth and fifth gears, that makes it feel so special.

Nail the throttle in sixth gear and copious torque available at 4500 rpm makes the motor as keen as ever. Where the standard engine is fast running out of answers, you now feel real acceleration. Drop a gear and your efforts are answered by a solid push in the back as the rev counter needle rushes into the red.

The much greater torque in the first half of the rev band changes the engine's character completely. Rather than the standard V10's aggressive high-rev behavior standing out in comparison to its relatively lethargic bottom end, you feel significant thrust all the way from idle to cutout. The smooth and progressive delivery disguises the car's true pace, until you look at the speedometer and the rate at which autobahn traffic is so easily caught and passed.

If you really want to sample the animal side of this engine, you just have to gun hard it in second gear with DSC disabled. The wave of torque breaks the big tires free in an instant, and the clever M differential coupled to a deft bit of steering and throttle craft will ensure a long and satisfying drift through third gear-and into fourth if you so wish.

The counterpoint to all this is the fact that in normal driving less revs are required to keep pace with the traffic flow, so the potential for better fuel economy is also there. With the bottom end now filled in nicely, the V10 becomes the consummate all-rounder.

At the root of this behavior is the old adage that there is no substitute for cubic inches, except more cubic inches.

"BMW's V10 is very powerful in standard form, but it lacks low-end torque," Oliver Nowack explains. "It needs high revs to really get cooking with gas, and because the M5 and M6 are heavy cars, the perceived time it takes for the engine to get on cam is quite long."

Where the standard engine has 4,999cc from a bore and stroke of 92.0x75.2mm, the 5.7 has 5,679cc from 94.2x84.0mm. "This is the only way to get 5.7 liters," Nowack says. "There is no space for larger diameter pistons or a longer-stroke crank in the crankcase. It is absolutely at the limit."

The new steel billet crank is another Cosworth masterpiece; the forged alloy pistons are from the renowned Austrian race piston maker, Pankl, and save 35 grams each. The valve pockets in their crowns are the same shape as stock, but enlarged to match the bigger valves. The race-grade, H-section connecting rods come from Auto Verdi in Sweden, save a quarter pound per rod, or 2.5 pounds for the set of 10. They cost €450 each-$660.

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