Hartge and Soul

It's nice to imagine emotion in car design, that when the first few graceful strokes of a roadster go down on paper, those responsible are inspired by the thought of sheer unbridled power blasting through the back wheels and leaving the world behind in a sheen of blurred scenery and flared pencil strokes.

Of course, the safety men have to stick their oar in, and the comfort man then waddles through the door. Last, but hardly least, the accountants get involved, and the fun really starts.

The result is a compromised and sanitized car. Did you imagine the first stylists on BMW's Z4 installed cup holders and Sat Nav on their sketchboards? Or left that much space vacant in the engine bay...?

Herbert Hartge, on the other hand, doesn't have a big team, and the accountant knows not to mess with him. What he says goes, so when he decided to shoehorn the M5's 400-bhp 5.0-liter V8 into the Z4 to create the Z50, a bizarre BMW-based homage to the AC Cobra, nobody stopped him.

Hartge has forced bigger engines into less space before, so mating the V8 M5 engine to the Z4 chassis proved a relative breeze--a matter of changing the subframe and mounts, marrying the electronics, fitting a new oil pan and tweaking the complete engine compartment and fuel system.

Just 110 lb heavier, the new engine bought another 170 bhp, a worthy trade. Hartge had to get more cold air into the engine bay to deal with the extra cylinders, achieved with a pair of gaping intakes in the new front spoiler and a larger radiator. The rear spoiler was modified for the dual chromed central exhaust outlets, a Hartge connecting pipe replacing the middle silencer.

On firing up, it doesn't bellow quite as belligerantly as some might want from a monster V8 at idle, but this car spends much of its time leaving modified M3s behind on unrestricted autobahnen and is, therefore, bearable if still aggressive at speed.

Besides, it's hard not to fall in love with a car that spits petrol from its exhaust at idle.

"Don't worry about the rev counter; it reads 6500 rpm as the redline, but ignore that this one goes past 7000 rpm," said Hartge's ever accommodating representative Joerg Wey as he talked me round his company's prize. "And the speedo is a little short, too. This car can do 184 mph--we're sure--maybe a little more!"

We never made it to the car's V-max, but 140 mph on a short stretch of autobahn convinced us it could back up all the power and speed claims and hype.

It's 25mm lower than the 3-liter Z4. Hartge fitted its own coilover shocks and 8x19- and 9.5x19-in. alloys, wearing Pirelli P Zero Rosso tires, 235/35ZRs up front and 265/30ZRs at the rear. The Z50 still soaks up bumps, as the company wanted a showcase that was not only fast but usable as well, but it felt rock solid through corners.

The power could be applied before the car was even at the apex, and the car swept through--gently breaking traction and pulling at the reins, providing the adrenaline while the tricky LSD provided a safety net wide enough to ensnare Enron.

The Z50 is skittish on chopped-up tarmac, causing lifted wheels and seductively soaring revs, but the sophisticated electronics kept the tail in line on landing. Such rigidity and agility breeds confidence, and it encourages hefty application of right boot from the off. Even under the most severe provocation around the winding country roads and hairpins surrounding the company's headquarters, the Z50 would only reward me with a steady and progressive slide.

This EUR98,000+ ($125,000) machine certainly marked itself out with its balance and chuckability by the end of our very short time together. It felt like a kinetic ball of motion, and had we not been in Germany, we would have been in serious trouble for the speeds we achieved. Driving anywhere else would be a frustrating experience in a car itching to climb the rev range.

The car breaks traction right through the first three gears, the 60-mph point comes in 4.5 sec., and the car keeps going, blasting past 100 mph in 9.6 sec. It will also do the quarter-mile in 12.7 sec., but even that can't come close to describing the sheer violence of visceral power battling for supremacy with the traction-taming technology.

The gearchanges feel sweet, if a little muscular, thanks to the Hartge short-shift kit and more purposeful aluminium gearstick that requires a real shove into the gate. The rest of the interior has benefited from the Hartge treatment, with aluminium pedals and other touches, but nothing too ostentatious.

To match its improved performance, Racing giant Brembo provided the 380mm cross-drilled floating-rotor vented front discs and eight-piston calipers, while the 328mm rear discs and floating calipers were taken from the M3 along with the slip diff. These respond with vigor when pushed hard, but are not knife-edge sensitive and require a hefty shove to push the car's limits of adhesion.

It's not the lightest sports car in the world at 3,234 lb, which is 297 lb heavier than the 3-liter Z4 but more than 530 lb lighter than the awesome Z8 with the same engine. It's also faster and cheaper.

And a clear example of a designer daring to dream, in the kind of company where accountants keep their mouths shut.

To read all about Hartge's program for the BMW X3 and 645Ci, and Nick's drive of a new Z4 from England to Germany, click here.