With a track to play on, the H50 V10 could have neatly toasted its rear tyres in the space of minutes in a full orgy of opposite lock, obscene speeds and ear-splitting noise.

The BMW 3 Series has become the workhorse of the masses and this machine looks only slightly different to the hordes of homogeneous class that pound the outside lane of our highways and byways each and every day. But this one is different; this one has V10 M5 power.

Hartge is a firm we visit regularly to sample their own individual brand of madness: oversized engines shoehorned into small BMW chassis. And here they have freed up 550bhp from the five-litre that propels the almighty new M5 and then slammed it defiantly into the body of a 3 Series Coupe.

And the result is a 1670kg rocket. With all five litres working hard this car scoots to 60mph in 4.4s and on to the supercar benchmark speed, this is a 200mph 3 Series.

None of the driver-centric crowd at Hartge’s Beckingen headquarters are fans of the SMG set-up, but they’ve made the best of a bad job to create the ultimate sleeper marked out only by the badging and subtle bodykit.

That and a speedo that ends beyond 330kph (205mph), as well as the homemade vinyl dashboard add-on that contains a gear indicator and all the vital information about gearbox set-up. As for the primeval noise and guttural vibration when the V10 clatters into life, well that’s when things start to get interesting.

Hartge didn’t just transplant the living, breathing V10 and seven-speed transmission from the M5. While it was on the operating table they fitted reworked cylinder heads, sports camshafts, a new engine map to reconcile the differing weight and a near straight-cut exhaust system to coax 550bhp and 390lb/ft of torque from BMW’s masterpiece.

We knew what to expect, then, a rev hungry driving experience that perhaps lacked the low down torque of a turbo. But it’s hard to evaluate such failings when the rev counter just keeps climbing towards 8000rpm and the H50 V10 tears up time and space between the corners. This Hartge is scary quick and leaves the M5 in its wake time and again on the de-restricted local roads. And it’s not hard to see why.

Powering to 60mph even the Pirelli PZero Nero rubber wrapped round Hartge’s own 9x20” fronts and 10x20” rears can’t contain the increased torque heading through the modified M5 axle. That’s the defining factor in the 0-60 time and this car could be even quicker.

With a clear road the triple digits come in no time as a click of the finger unleashes a new wave of acceleration, of blood lust, that can take this machine to outrageous levels in moments. It’s an unadulterated license loser as that rorty, detuned F1 exhaust note feels like it could bully Ferraris into pure submission.

The only downside is the thuggish engine note through the bends, as a near as dammit straight-cut exhaust, for export only, cut like a buzzsaw through the forests. The car blips the throttle to match the revs on downchanges and with a near race exhaust

It’s supercar fast and takes just a click of the finger on the wheel-mounted shift to keep pace with the constant surge of acceleration as Hartge brought all the electronic assistance over from the M5 and the car will pretty much drive for you.

And thanks to the road-tuned suspension this car will nudge into understeer before sliding round ever so progressively at the rear on a hard charge and only with serious provocation. They’ve taken every spare millimeter in the engine bay, but Hartge claims the famous BMW equal weight balance has barely shifted and now sits at a more then respectable 52:48 front:rear.

The Coupe comes with Hartge’s own suspension system, too, which is full adjustable and drops the car up to 30mm. That makes it a near racing car for the road, the works M3 is now upon us and can be had for far less money, but that won’t come close to this car.

Only the high-pitched scream of the engine through that lightweight exhaust gives away the rate of knots and belies the serene sense of calm exuded by the chassis at speeds that should have preceded a major incident. And even then that’s insulated inside the car and it was photographer Fraser that explained just how evil this car sounds as it heads past.

On the brakes into a bend the car blips the throttle with a near predator-style snarl to produce the perfect downchange and in all that’s left to do is hurl the car in with ever more ambition. That low-slung stance and acres of electronic controls going on through the M5’s three Playstation’s worth of computer chips mean the car simply never fails to stick, even when asked for the impossible.

With a track to play on, the H50 V10 could have neatly toasted its rear tyres in the space of minutes in a full orgy of opposite lock, obscene speeds and ear-splitting noise. It’s just too good, too fast, for the public road and this unofficial M5 CSL is every bit as controlled at sane speeds as a modern day hypercar.

True entertainment takes truly insane speeds, which will land you in jail even in Germany, so this is a weekend and track warrior at best and the sound insulation, dressy carbon-fibre pack and relative comfort inside the car might just as well make way for a rollcage and track harness.

From the outside the H50 keeps things subtle but is sleeker than the saloon, with its ground-hugging profile more suited to a high-power conversion and accented here by a cutting front lip spoiler that provides some much needed impact, side skirts, rear lip spoiler and a new rear apron. That houses the four exhaust pipes that signify an M car in the making and the 20” Hartge wheels may be more than you’d want.

Hartge has accentuated the wedge shape of the base 3 Series and given it the thrusting forward motion that Munich couldn’t. Of course the Beckingen firm is on a tough wicket there, as building a supercar from something so ugly and then asking €160,000 for the privilege of ownership is pushing things. It’s the ultimate sleeper car, though, and the ultimate expression of the SMG at work.

Hartge H50 V10 Coupe Test Drive