Blown Dynamite

'Mundane' is not a word you'd usually use to describe BMW's M Coupe, but that's exactly how a standard "coop" feels after spending time with the 360kW Rob Green Motorsport version. In fact, there's not much this side of megabuck supercars that'll stick with the Meanest Green Machine yet.

For openers, how does a 0 - 100 km/h sprint time of 5.29 seconds sound? Or a 0 - 400 metre dispatched in 13.51 seconds at a terminal speed of 175.1 km/h, with the kilometre dispensed with in a scorching 24.09 seconds at a mind-boggling 225.7 km/h? And, for an encore, the ferocious blue Coupe only stops accelerating at 278.5 km/h - and then due to the intervention of the revlimiter rather than because of a lack of power. Shortly after being tested by the author, the revlimiter was raised to 8200 rpm, enough to see the BMW run to a theoretical 303 km/h VMax.

Ferocious is the only word to describe this car, and the first time you crank the 3.2 litre straight six into life you know it means business. In addition to the rumble from the big six, there's a deep and spine-chilling whistle emanating from under the bonnet . . . it's the sound of a supercharger being turned by a crankshaft drive belt, forcing air into a custom-made plenum chamber via an air to air intercooler.

Over here in South Africa, Rob Green of Rob Green Motorsport has built an enviable reputation as a craftsman when it comes to his supercharger installations, and the BMW's underbonnet aesthetics are a joy to behold. Every pipe, bracket, joint, hose and clamp is of the highest quality, made from the best materials using the latest engineering techniques to ensure maximum reliability and durability. In a number of cases, components are designed on computer to ensure their integrity.

This particular installation uses a Vortech V1 blower, in what is termed "SC" trim. This means that it has an impeller tailored by the USA-based company to meet Rob Green's specific requirements, including South Africa's unique high altitude, high temperature conditions. About half of the country's passenger car sales take place in what is termed the Highveld region, which means much of our motoring is done at altitudes between 1,500 and 1,800 metres above sea level. Which makes you understand why forced induction is so popular in the aftermarket.

But the other factor is summertime temperatures that regularly exceed 30 degrees Celcius, so big intercoolers are called for, while many top tuners believe that a crank-driven blower is the only way to go if decent throttle response is to be maintained. On a hot summer's day, turbo lag can be a real problem.

This car runs maximum 0.9 Bar boost at Reef altitude, and about 1.1 Bar at the coast, with the standard 10.5:1 compression ratio lowered to 8.5:1 to ensure reliability. The drop in CR is achieved by using a 0.5 mm laser-cut steel shim plate, sandwiched by two standard head gaskets.

"It might sound simple, but don't try this at home," grins Rob Green. "As well as lowering the compression there are a number of additional processes we go through, and on all cars I first conduct a cylinder leakage test to ascertain if the motor is fit for this kind of conversion, and then use a top-notch lubricant. We highly recommend using a synthetic oil and in this case we used Castrol RS, to keep temperatures within the manufacturer's specifications."

Intercoolers are locally manufactured to close tolerances, and while the surface area is compact, they provide a reduction in temperature of between 30 and 40 degrees Celsius with minimal pressure drop. All piping is 60mm black powercoated steel with pressure lips at either end, while the actual couplers are made from silicon rubber piping with stainless steel clamps.

As with all Rob Green Motorsport conversions, the watchwords are presentation, quality, and durability.

Greg Morris, an investment banker and owner of the Coupe featured here, has cut no corners in giving his Beemer the wherewithal to run with cars costing two or three times as much. Which means it boasts the optional aluminium plenum chamber (the part of the inlet manifold that dispenses air to individual inlet tracts) which is about a quarter of the volume of the standard item and ensures instant throttle response. The ram tubes to the cylinder head are carefully designed to be of equal volume.

Special 36-pound fuel injectors work in conjunction with a rising rate fuel pressure regulator that increases the delivery pressure as the boost level climbs. The engine electronics have been extensively revised to perform an equally heavy-duty task, and the standard air mass meter is dispensed with and a Manifold Absolute Pressure sensor used in its place. This component works in tandem with the original BMW engine control unit and a Unichip piggyback computer to ensure the perfect mix of air and fuel no matter what the altitude, the temperature, engine load, or any other combinations of factors. To prevent tampering, the Unichip is encrypted once the best settings are found on the dynamometer - a standard Rob Green Motorsport practice.

With so much additional air being pumped into the engine, there's a huge need to get it out in a hurry, and a 63mm diameter stainless steel exhaust system - designed and manufactured at the company's Gauteng province premises - ensures the rapid exit of spent gases. Air into the engine is filtered by a high capacity BMC performance filter, with intake air being collected in the high-pressure area down at bumper level.

The end result of all these modifications is there for your right foot's pleasure, but they are as impressive on paper as they are in the real world. This car makes no less than 360kW at 7500 rpm, and thumps out a staggering 510Nm of torque at 5200 revs. But before you jump to the conclusion that the engine is a tad peaky, consider this: while the standard car's maximum torque of 340 Nm arrives at a user-friendly 3250 rpm, at that juncture the RG version is already making 390Nm, and swelling rapidly. It is a blindingly quick car, yet incredibly docile in day-to-day use.

Rob Green also offers two additional items for his bespoke, supercharged Beemers, both of which were fitted to this full-house machine. They include an uprated clutch/flywheel assembly, and a short-shift gearlever. The former includes a steel flywheel reduced in mass from 12.7 to 7.3 kilograms, and a competition-style copper button friction plate with an upgraded pressure plate. Planning on doing a lot of robot racing? Then this clutch is a must-have.

The short-shift gearlever is one of very few cosmetic changes to this car, and comprises a gearlever, gearlink support, and one of a choice of three gearknobs.

"The supercharger conversion turns the MCoupe into one of the ultimate performance cars, and the figures really say it all," says Green. "These engines are good for 8200 revs, and now that we've moved the revs up to that point and with an additional high pressure fuel pump fitted, we reckon we've got the engine speed and the juice to crack 300 km/h - even at this altitude."

As an option, owners could go for a conversion that replaces the original Mcoupe five-speed hardware with a BMW six-cog unit, or a longer final driver. Whatever the customer opts for, they'd have the kind of top speed once the preserve of Ferraris, Porsches and Lamborghinis . . .

And it'll cost a fraction of the price. The full-house drivetrain conversion, including the aluminium plenum, clutch/flywheel assembly, remapped engine speed limiter and gearlever, comes in at 85 000 South African Rands, or around 14 500 Australian Dollars at current exchange rates.

Standard BMW M-Coupe Versus Rob Green Motorsport Supercharged Version Acceleration Std (seconds) RGM (seconds) 0 - 60 km/h 2.89 2.62 0 - 80 km/h 4.37 4.00 0 - 100 km/h 5.89 5.29 0 - 120 km/h 8.08 7.37 0 - 400 metres 14.10 13.51 Terminal speed 163.7 km/h 175.1 km/h 0 - 1000 metre 25.47 24.06 Terminal speed 212.9 km/h 225.7 km/h Top speed 250 km/h 278.5 on revlimiter Power 228 kW at 7400 rpm 360 kW at 7500 rpm Torque 340 Nm at 3250 rpm 510 Nm at 5200 rpm All performance data compiled by Roadworks CC, using a Datron M3 microwave sensor.