Nick Hall drives the 400bhp, M5-engined BMW Z4 inspired by the Cobra’s venom…
The centrepiece of a thousand mythical motoring yarns, the AC Cobra is a legendary beast born by accident, much like Champagne and VX poison nerve gas – at opposite ends of the celebration of the life/horrible blistered death spectrum.
AC’s Ace was nothing to write home about and would have been a mere footnote in the history of roadsters had Caroll Shelby not persuaded them to ditch the Ford Zephyr unit and opt for a big V8. Thus a legacy was born, and four decades on it has proved the inspiration for another madcap conversion.
The Hartge Z50 is different, of course, and is based on wholely German engineering, but Herbert Hartge maintains that the Cobra was in his mind the whole time when he conceived his Z4 conversion.
It’s not that BMW’s initial engine range was puny, with the 3-litre managing a solid 231bhp. But this car has 400bhp at 6900rpm and continues well past 7000rpm, thanks to a heart and lung transplant from the Autobahn-stomping M5. It has the same engine as in the all-powerful Z8, with 200kg less to carry around, which makes for a mouthwatering recipe.
The engine note is not brutal, although it’s obviously loud, thanks to some common sense from the Hartge fabrication unit. Knowing this car could be expected to run for hours at a time at high speeds on the motorway system, they limited themselves to replacing the middle silencer with a connecting pipe.
This allows the five-litre unit to let everyone know it has arrived, but would not send the driver steadily insane at 160mph on the long schlep from Munich to Berlin.
Fitting the V8 required modifications to the subframe, engine mounts and wiring looms, and a few other oddments including a larger radiator. It was an easier job than many might think though. Hartge has been forcing big BMW engines into small spaces for two decades, starting with a 3.5-litre 7-series engine and a 3-series chassis in the ‘80s.
The engine and gearbox - also a six-speed carried over from the M5 - weigh just 80kg more than the disposed of items. They bring an extra 170bhp making it a good trade.
The performance figures are astonishing. Not only does this firebrand career to 60mph in 4.5 seconds, it keeps going past 100mph in 9.6 seconds and 124mph (200km/h) falls in 12.4s. This Z4 silhouette keeps going all the way to 184mph, a V-max that has been thoroughly tested on derestricted German roads.
We didn’t find the gap in traffic to unleash the machine’s full fury, but hitting 140mph with the top down in seconds, and losing valuable paperwork from the car in the process, was enough to back up all the claims on straightline performance!
It’s low down where the power really tells and the Z50 spins its wheels enough in the first three gears. It has enough grunt to leave the road with emotional scars, and short shifting with the help of the muscular Hartge sport shifter becomes a prerequisite after reeling in the horizon at an alarming rate of knots.
Straight lines are one thing, cornering is quite another. While the Z50 seems happy to scrabble for traction in a straight line it has an array of devices for keeping the tyres driving forward in the corners.
The standard Z4’s suspension is something of a letdown, that is the general feeling in the British press. Some say its too crashy and others, like me, don’t believe it has the road holding ability to mix it with Porsche’s Boxter – its logical opposition.
It is perhaps not surprising then that Hartge ripped out the original system and started from scratch. The Z50 has been fitted with an entirely new adjustable coilover suspension created in house and sitting much lower than the original, which is obviously set on the firm side but came into its own round Beckingen’s sweeping roads.
The original BMW Z4 2.2-litre boasted a 50%/50% front/rear weight distribution, and the installation of the V8 has tipped that forward just 2%. Shorter than the inline six, the M5 engine adds just 30kg to the front axle and that is accommodated by a myriad of other tweaks in the chassis and suspension department.
The Z50 doesn’t soak up major bumps, preferring to lift a wheel and rev freely under serious provocation, but it doesn’t roll either and this means the power can go on way before the exit and the car can be induced to break traction.
It won’t stray far, thanks to the tricky Limited Slip Diff that has been imported from the M3 and BMW’s Dynamic Stability Control. After a few attempts it felt perfectly natural to enter the corner in a slide. Even on maximum attack the Z50 drifted uniformly round the corner (with the traction control turned off).
My signature on a €2500 insurance excess guarantee prevented further exploration of the car’s limits, but suffice to say the diff provides a safety net big enough for a tightrope walking Rik Waller (we can only dream) and will catch all but the most foolhardy driver while providing bags of entertainment.
Few cars walk this tightrope of composure and fun so comfortably and it was this that stood out. Normally a V8 like this needs to be treated with kid gloves in the acclimatisation stage at least, but the Z50 didn’t need this.
Racing giant Brembo provides the 380mm vented front discs and eight-piston callipers, while the 328mm rear discs and four-pot callipers are taken from the M3 along with the entire rear axle, modified of course, and the slip diff. These are certainly sharp, as you’d expect, but were no more frightening than the stoppers on the TVR Tuscan S, which is a similarly powered manufacturer-produced road car.
It’s a solid comparison, with the Z50 having similarly testosterone-fuelled blood coursing through its veins. The Hartge felt if anything a little more stable than Blackpool’s rocket – certainly on the bends. That said it costs €98,675 + Tax (£66,000 as well as the German treasury’s cut), so it should prove the master of more or less anything on the open market.
That money certainly hasn’t gone on window dressing, as the Hartge Z50 is a subdued supercar and not much different from BMW’s base car at first glance. Yes it’s lower and yes it has different wheels and 5.0-litre V8 badges on the side, but they’re small and hard to spot at 150mph.
Inside the standard trim has been embellished with logos, but certainly it hasn’t been overdone. Hartge’s reasoning is that this is a sportscar and if it goes fast and is great to drive then it doesn’t need to look like Liberace’s coffin. It does sit on 8x19 and 9.5x19-inch alloys wearing 235/35ZR19 and 265/30ZR19 on the front and rear respectively, clothed in Pirelli P Zero Rosso tyres, but Hartge will argue the lightweight wheels are all part of the performance package.
What the super wealthy owner will get is one of the few certificates in the world to say that this is a genuine Hartge Engineering car. It is not a BMW, anymore, and has been registered as a one-off creation. It’s difficult to say whether this unique concept is worth the money, but this is certainly a barnstorming leisure car.
Sadly the price alone will prevent the Hartge Z50 ever truly becoming the AC Cobra for the Pepsi generation. But as a glimpse of what could happen if the BMW board suddenly went quite insane, perhaps after a heavy session on the Champagne and VX, it’s an inspiring sight indeed.
Photography Copyright © Thomas Angus 2004