This is a 440bhp, tri-turbo diesel BMW Z4

Meet the FrankenBeemer. It's a one-off concept car built by BMW tuner AC Schnitzer, which started out in life as a humble, naturally aspirated straight-six engined roadster. It's not that anymore.

But then one look at the orange wheels is enough to tell you that. AC Schnitzer used the old sDrive 23i - which, in the vagaries of BMW's nomenclature means it was actually a 2.5-litre sixer - and binned the engine immediately. It then transplanted the heart from the M50d; that astonishing triple turbo, 3.0-litre diesel.

Some wizardry happened, and a whopping 440bhp emerged from the engine - up from the standard M50d's 381bhp - together with 620lb ft of torque. To better handle this power, the rear axle from the old V8-engined M3 was fitted, together with an eight-speed auto ‘box and race suspension.

There's more. The folding metal roof was replaced with a carbon fibre fixed setup, there's a carbon fibre bootlid, lightweight exhaust, carbon fibre bucket seats, and lightweight, orange alloy wheels. Overall the whole thing weighs in at 1469kg - considerably less than the 1600kg sDrive 35i, and a kilo less than the base sDrive 18i.

The result? This little Z4 with an M3 rear axle and an M50d engine and orange wheels will accelerate from 0-62mph in 4.0 seconds, 0-124mph in 12.9 seconds, and top out at 173mph. Not bad at all for a diesel. In fact, not bad at all for, well, a sportscar.

Of course, AC Schnitzer doesn't plan on making any more of these, building this one purely as a technology showcase. For reference, this one cost over £82k (€114,000). We suspect if you ask them nicely, they'll probably make you one too...