The 5.0-liter S85 V10 that landed in BMW's E60 M5 in 2005 remains one of the most memorable, charismatic performance engines ever fitted to a road car. But what would happen if one were to punch it out to 5.8 liters and drop it in a far smaller vehicle - say, a two-seater?

One German outfit was crazy enough to try: tuning shop Manhart Performance. The car has actually been around for more than a minute, garnering coverage (and enthusiasm) from a few big-name automotive publications, but a new video from has thrust this monster of a tuner car back into the limelight.

The E60-generation BMW M5's factory V10 was unusual for a road car motor, and a world first in a four-door sedan. It was born out of BMW's participation as an engine builder in F1 racing, featuring a sky-high 8,250-rpm redline and an impressive 500 peak horsepower.

But after some fiddling with from Manhart and a substantial increase in displacement, the engine in this BMW Z4 is making 621 hp, and sounding as good as ever doing it. Not that there's anything wrong with the Z4's original inline-6, mind you, but when you have the opportunity to pick up a few hundred extra horsepower, you take it.

Manhart's M5-powered BMW Z4 certainly looks the business, too, with rear badges that read "V10" and "600," likely a reference to its approximate output rating in PS, along with quad exhaust outlets, and some aggressive-looking matte-black wheels with gold rim stripes to match its slick gold vinyl side and hood graphics.

The Z4 recalls another unique build that's amassed some notoriety in automotive circles: the Hellcat-powered "Hell Kitty" Mazda MX-5 Miata. That car proved to be such a handful that, last we heard, it was crashed back in February. All this is to say: if you're going to put some 600 hp or more in a small, lightweight sports car, be sure to exercise extreme caution.