Bimmer

The objective: Take an already-potent BMW M-roadster--a machine designed for top-down driving fun and frolic with an attitude--and add even more power to its taught, hunkered chassis. Of course, tuners and engineers can achieve this several ways.  They can add displacement. They can increase airflow. Or, they can spin the engine faster to process more air with the appropriate additional amount of fuel. They might also reconfigure the engine to burn more volatile fuel. The final method, and in any ways the most efficient one, is to go with forced induction by hanging a blower on the front of the engine. In the case of this Southern California BMW Specialist, he took to the air.

More power is the last thing a car that can already sprint to 60mph in 5.2 seconds actually needs. But power corrupts, and we live in a deliciously corrupt society. So, if you're going to sneak a blower under a BMW M roadster's  hood,  you may as well have someone like Osh Minelian at Race Marque Systems strap on a pocket protector and fire up the PC to engineer the job.

What started life as a 3.2 liter, 240 horsepower car can now blast forward like a 350-plus-hp supercharged wind machine, while swiftly exiting Van Nuys in Southern California's densely-populated San Fernando Valley, Race Marque System's home.

The addition of a mechanically driven supercharger does provide a telltale whine, most noticeable when the car is lugging along near 1,000 rpm . The excellent around-town driving characteristics of the M roadster remain. This is a great relief--a majority of everyone's commute these days seems to trudge along congested highways, and not just in Southern California's sprawl.

Once revs increase, the gear noise becomes less noticeable as the throaty exhaust note takes over. The efficient S-Trim Vortech works very well with RMS' engine tuning, as the inline-6 begins to build boost at 2,500 rpm. By 3,200, the curve grows stronger, until  the engine starts pulling like an atomic particle in a linear accelerator above 3,900. The progressive power curve, coupled with the remarkable M roadster chassis, makes the care relatively easy to drive, especially when negotiating a series of tight mountain curves. In fact, the car's seemingly docile nature might lull a driver into a mistaken sense of security. One swift jab of the throttle can fairly easily send the rear end sideways. In the wrong place at the wrong time, this will definitely get your attention.

Another example of this cars fierce energy is its incredible 0-60 mph performance. BMW states their US-specification M roadster will reach 60 mph in only 5.2 seconds. With no modifications beyond those described so far, the RMS M roadster blasts to 60 mph in only 4.1 seconds.

Good driving sense is paramount when piloting such a high-horsepower, short wheelbase car. According to Minelian, the 7.5-psi-boosted engine produces 356 horsepower at 6,500 rpm, an increase of 116 over stock. This surpasses the 321-hp European M roasdster, and doest require screaming revs to do so. It also spits out far more torque than the either the US-specification or Euro car--307 lb-ft. Though you'd have to be geeky as Barney Fife to do it, you could lug the RMS car around in one or two gears too high for conditions, and it wouldn't complain.

The heart of the RMS system is Vortech Engineering's S-Trim centrifugal supercharger which tucks neatly under the hood. Vortech's internal gear-driven unit was selected for reliability and naturally, performance. While it's externally driven by a belt off the crankshaft, as are all centrifugal superchargers, internal belt failure will never occur. The compressor map for the S-Trim is broad and efficient, demonstrating that a carefully configured engine will benefit throughout the rpm range.

Proper  air/fuel mixture and ignition timing is always critical with forced induction systems. The RMS kit uses larger Bosch fuel injectors controlled by RMS software to optimize this application without the use of additional fuel enrichment Band-Aids. (For more on computer programming, see sidebar.)

Proper mounting of the blower is important, so RMS machines a 3/8 inch think aluminum bracket on a CNC (Computer Numerically Controlled) machine. The bracket uses several attachment points. The black anodizing of the mounting plate adds a fine touch to the already darkly accented BMW engine bay. Its also finished with a CNC-machined RMS logo facing forward. All bolts are grade A and black oxide finished. Also allen head screws site in the machined recesses on the mounting plate. A specially-fabricated black compressor discharge pipe neatly connects the supercharger to the intake plenum of this U.S.-specification M engine.

RMS also uses a set of larger-diamter billet aluminum crankshaft and supercharger pulleys, providin more belt wrap, This practice helps prevent the 6-rib supercharger belt from slipping, a condition which can be annoying on unites with smaller pulleys. Slipping belts create an irritating squeal and diminish horsepower due to reduced impeller speed, akin to a torque converter slipping when you don't want slippage. A belt which slips also overheats, inviting premature failure, which is more a pain in the ass than a pain in the parts.

That masterfully hip crank pulley is  machined for both a supercharger belt as well as the power steering pump drive. This makes for a much cleaner design by preventing a stacking of pulleys.

Good internal supercharger gear drive lubrication is also important. The RMS setup extracts oil from the stick oil pressure switch mount, located on the oil filter housing. This allows the installation of additional oil sensors for an optional gauge cluster which reads oil temperature, oil pressure and boost pressure.

Once a small percentage of engine oil is circulated through the supercharger's gear drive housing, gravity drains the oil back to the engine through a specially fabricated dipstick tube. Minelian expresses a concern with the conventional method of drilling a h ole in the aluminum oil pan, then installing a brass fitting for the drain hose. "Particles of aluminum may enter the oil pan during the drilling and tapping process, " he warns.  "The modified oil dipstick tube adds costs to the kit, but it prevents harmful contamination in an expensive engine."

RMS also backs their setup with a 24-month, unlimited mileage guarantee; something not all companies offer. For individuals looking for even more oomph, RMS is developing a Stage 2 version using a larger mass air sensor and an intercooler. For the sun and fun worshippers of this country RMS Supercharged M roadster is seriously rapid transit with the top down.