This one-off ‘858 CSL’ is a stunning 630bhp, V10-powered BMW 8 Series

A company in Southern California has treated BMW’s classic 8 Series to a light, gentle refresh. And by light, gentle refresh, we of course mean completely changing its personality and looks from a relaxed Nineties GT into a snarling, V10-powered lightweight.

Welcome then, to Reyn Speed Shop’s 858 CSL. And unlike modern BMW nomenclature, that badge actually signifies exactly what this car is. So yes, there is a 5.8-litre engine lurking underneath that long, modified bonnet. And yes, it is Very CSL.

Engine first. Out went the original 8er’s engine, and in came a modified, embiggened version of the E60 BMW M5’s 5.0-litre V10. Why a screaming V10? “To keep with an exotic and technically advanced drivetrain, the E60 S85 was the ticket for us,” Reyn Speed Shop’s Rey Rivera told TopGear.com.

Rey enlisted the services of Carbahn - which keen BMW enthusiasts will immediately recognise is Steve Dinan’s tuning company - to build the M5’s V10 out to the 5.8-litre ‘street’ spec. Rey hasn’t yet dyno-tested his 858, but reckons it’ll punch out at least 630bhp and 489lb ft of torque. Considerably more than a tired old 850i’s V12.

Your arms might get tired, mind. Keen BMW enthusiasts will also remember US-spec E60 M5s got the option of a six-speed manual, and that’s the gearbox slotted into this 858, attempting to harness 630 horsepowers to the tune of… some speed. Rey hasn’t tested its performance yet, but let’s just assume it’ll be ‘Much’.

Ditto the noise. “You can’t beat the sound as well as the flexible power band that motor has to offer,” Rey said.

Suspension? “The car sits on stock EDC front and rear shocks and struts,” Rey said. “We are working with Moton to create a four-way system for the 858 CSL as the car is 689lbs lighter than a stock E31 850i, and we think we can better dial it in with that system.”

Six hundred and what now? Ah, right, that’ll be the Very CSL bit. Rey – working with Jon Sibal – designed a modified bodyshape for the 858 that somehow strips 313kg of bulk from the 8er. That means the car weighs in the region of 1,500kg. You’ll of course be very familiar with Jon Sibal’s fine back catalogue, who together with Rey decided to work in some very familiar elements into the 858.

“When Jon and I met the criteria was to stay within the BMW classic M design elements,” Rey said. “I think you can spot those when you look at the car.” He notes the E30 M3 for its flared arches; the E39 M5’s front valance; whispers of E46 M3 CSL in the integrated rear spoiler, and even the lovely Vader seats from an E36 M3.

“I’m only a small cog in a team of professionals putting in much effort to make Rey’s V10 vision a reality,” Jon added.

Naturally all the body panels are crafted out of carbon fibre – explaining the drastic weight loss – while the classic 8er’s pop-up lights have been swapped out for vents instead, likely to help further cool down that very angry V10 inside. Gives the ol’ lug a cool modern twist.

“The E31 styling carries its age so well we obviously kept the E31 interior, and just integrated some E60 controls where needed,” he added. The fact there’s so much E60 M5 plugged and very much playing inside the 858 CSL means maintenance and getting parts would be a breeze.

Indeed, that formed part of the philosophy behind this build. So why, TG asked, did Rey pick the E31 and fill it with M5? “We wanted to create something special and more modern to stretch our abilities,” he said. He did a tonne of research and discovered the E31 and E60 could be melded together using creativity and witchcraft, thanks to a lot of similarities between the platforms.

“One big aspect of what we wanted to achieve was to build a restomod that had full integration of OEM-level diagnostic as well as service and parts replacement capabilities. We were able to achieve that by fully integrating all of the components from the E60 into the E31 chassis.

“Here we are with the end result,” he added. And it’s some result; the work of four years’ worth of labour and countless hours hunkered down in the garage.

And the train doesn’t stop here, either. What’s next, we asked? Well, Rey only mentioned that he has ‘some ideas’, involving a 5.4-litre V12 running individual throttle bodies, a six-speed manual gearbox, and an old E9. Another light, gentle refresh incoming…

Photography: @precisionsport/@klapped.media
Renders: @jonsibal