One-off BMW '858 CSL' boasts a 630hp atmo V10

You'll often see fancified badges tacked onto the back of BMWs, many of which are a vein attempt at pretending the owner bought an M model, but the '858 CSL' badge on the back of this E31 8 Series actually signifies what's hiding underneath.

Built by Reyn Speed Shop in Southern California, this custom build has exactly what it says on the tin. The big GT car has been turned into a comparative lightweight, explaining the CSL badge, while there's a 5.8-litre V10 stuffed under the bonnet to justify the numbers.

Using the 5.0-litre S58 engine from an E60 M5, the naturally aspirated 10-cylinder has been enlarged to 5.8-litres by Carbahn. While untested on the dyno, it's now estimated to produce around 630hp (470kW).

Curiously, it's backed by a six-speed manual which was available on the E60 M5 exclusively in the United States.

Beyond its underpinnings, the 8 Series' body has been completely reworked. Although it's considerably wider, particularly at the rear, an astonishing 313kg has been carved out of the original bodywork.

Now tipping the scales at around 1500kg, it still looks the part thanks to its tweaked design elements coming from other BMW models. For instance, the flared arches draw upon the E30 M3, while the front valance is a nod to the E39 M5.

The interior is largely the same as the E31's original, although plenty of features from the E60 M5 have been slotted inside it along with a set of E36 M3 'Vader' seats.

As unique builds go, this one is right up there. The original 8 Series might be a less widely beloved model from BMW's back catalogue, but this one shows just what potential the model still holds.