It's been a tough couple of years for BMW M fans. First we saw the M badge applied to a pair of SUVs, followed by the demise of the fabled high-revving normally aspirated M engines - only the M3's V8 remains, and that'll soon be replaced by a production-based blown straight-six.
Naturally, purists mourn the passing of these fantastic engines, but times change. With the demand for greater efficiency and cleanliness, there's no place for the E60 M5's wonderful V10. So the F10 M5 followed the trend for downsizing and turbochargers, borrowing the X5M's V8 motor and ushering in a new age of M-Power that's less manic, more refined.
The switch to forced induction brings one obvious benefit: ease of tuning. Where the high-strung V10 had approached the limit for a normally aspirated 5-liter engine, the V8's turbos offer an easier route to dialling in more horses. And while the 560hp M5 4.4-liter V8 could never be described as anything other than highly tuned, the development work for tuners generally involves software rather than extensive hardware upgrades.
This isn't to suggest that Manhart Racing (MHR) hasn't been typically thorough with the engineering of its F10 M5-based MH5S Biturbo. Engine output is tweaked with a carefully reprogrammed ECU and improved breathing thanks to great looking carbon airboxes plus a complete stainless steel exhaust system.
The result is 646hp, representing a 16% increase over stock, and 570 lb-ft, elevating the M5's performance to an even higher plane.
In truth, opportunities to use all the performance are few and far between - even on Germany's de-restricted autobahns. The MH5S gathers speed with such ferocity, that you quickly find yourself travelling massively faster than any of the surrounding traffic.
Our first foray onto the 'bahn saw us spear past 175mph with ease, the DCT transmission serving up a wave of unrelenting thrust that suggested plenty more to come.
Manhart Racing claims the MH5S will hit 196mph (316km/h) flat-out after the new software removes the 155mph factory speed limiter. And from our experience, we'd certainly believe every last km/h of it.
The transition from mooching around town to pinning the speedo on the autobahn demonstrates a Jekyll and Hyde character. The low speed refinement and silky transmission provide sharp contrast and added shock value when the MH5S responds to full throttle.
Of course, much the same could be said of the standard M5 but in the process of extracting more performance, MHR added some personality to the M5 recipe.
While a great deal of its new personality comes from the firm shove in the back, it's the carbon airbox (GruppeM on this car, but MHR is developing its own setup) and custom exhaust that contribute most.
It's amazing how more noise can define the character of a car; in the MH5S it's the defining trait as the engine snorts, snarls and growls up and down the rev range.
Crack the throttle open at low revs and you hear an underhood tornado as boost pressure grows and pressurized air is forced into the engine - an aural warning of the impending onslaught of forward motion. Back off the throttle and there's a huge 'choooof' as excess boost is dumped into the atmosphere; the childish among us will provoke this intentionally (me included). Stay with the throttle though and, as boost rises, the engine gets into its stride. The exhaust note hardens, the V8 rumble giving way to an aggressive blare as rich, powerful sounds flood the cabin from the MHR stainless steel exhaust system. It's an impressive aural performance that's sheer entertainment and sets the MH5S apart.
On top of this is a selection of aesthetic alterations that give the subdued M5 a more imposing look that cleared the overtaking lane rather well. The trump card, the piece that grabbed our attention but would damage your wallet most, was the custom carbon hood with integrated vents, evoking the M3 GTR and aiding engine cooling.
A stroll round the MH5S also revealed a new front spoiler, rear diffuser and trunk spoiler also finished in bare carbon fiber. This particular car was even treated to a matte grey wrap providing greater contrast to those carbon fiber parts that tied everything together.
The cosmetic pieces don't detract from the business of getting from A-to-B as quickly as possible. Aiding the MH5S in its role as a supreme mile-muncher was an adjustable KW Clubsport suspension system unique to MHR, which dropped the MH5S closer to the ground (possibly too close for daily use).
The car sits on a set of 21" three-piece MHR08 wheels supplied by American company ADV.1. They're wrapped in 265/30 front, 305/25 rear Michelin Pilot Super Sport tires; seemingly the rubber of choice for many top tuners these days...
They do a fine job of sticking the BMW to the black stuff, while the firmer damping all but eradicates body roll when pressing on.
The ride quality remains surprisingly compliant despite the skimpy sidewalls, but you're always aware of the 4400 lb curb weight. The nose wants to push in tight turns, and the huge wave of torque easily lights up the huge rear tires if you're running in one of the more relaxed modes.
The MH5S is better suited to fast, sweeping country roads and freeways than tight turns, where it's high-speed stability, immense grip and precise steering come to the fore.
All tuners are in the business of pushing the performance envelope beyond the point where the manufacturers leave off and by tweaking the M5, Manhart Racing has infused the car with a healthy dose of character in the process.
From the snorting histrionics of the carbon induction system and custom exhaust, to the added aesthetic attitude, and the fact the MH5S Biturbo can turn harder than the stock M5, it lays down a marker of what's possible with the F10 M5. And with other companies developing their own conversions, we're sure this sports sedan has even more to offer.
2012 BMW M5
Engine 4.4-liter V8 32v S63TU twin-turbo with Manhart Racing ECU software, cat-less downpipes and stainless steel exhaust system with 90mm tailpipes and valve control, GruppeM carbon fiber intake system
Drivetrain stock seven-speed DCT transmission
Brakes stock, painted calipers
Suspension MHR/KW Clubsport coilovers
Wheels & Tires 21x9.5" f, 21x10.5" r MHR08 Deep Concave wheels by ADV.1, 265/30 R21 f, 305/25 R21 r Michelin Pilot Super Sport tires
Exterior Manhart Racing carbon fiber vented hood, front spoiler, rear diffuser and trunk spoiler, matte grey vinyl wrap, MH5S Biturbo stripes and MHR badges
Interior Manhart Racing badge and floor mats