Test drive of MTM’s Amazing Supercharged B7 Audi RS4 Clubsport!
The MTM RS4 Clubsport. What praise can we possibly give to the regular RS4 that hasn’t already been said? It’s simply a phenomenal and highly-capable 4-door unlike anything else available. In stock form it’s good enough to lap the Nürburgring Nordschleife quicker than any other 4-door sports sedan on the market. It’s exceptionally luxurious and well equipped. It also comes with the tried and proven all weather conquering quattro driveline now with a rearward torque bias. It’s not perfect to all people though. And so where there’s room for improvement MTM steps to the proverbial plate.
The centerpiece of the MTM RS4 Clubsport package is the liquid-to-air intercooled, Lysolm-type, belt driven supercharger that resides directly underneath the carbon fiber bulge on the hood and feeds the car with 0.45 bar (6.5 psi) of fresh air. This cleverly designed package sits smack dab between the cylinder heads within the “V” of Audi’s 4.2 liter V8 and boosts power levels to a very impressive 535 horsepower and 428 ft-lbs of torque. The engine internals and compression ratio remains 100% stock. A special carbon fiber vent on the hood gives extra clearance to the supercharger and helps keep underhood temperatures checked. The blower assembly completely replaces the stock variable length intake manifold.
It’s important to note that the RS4 Clubsport is still a prototype, meaning it is quite clearly a work in progress. The final version will certainly be finely finished and up to OEM standards and aesthetics, as with all MTM vehicles. The particular supercharger on this press car has actually been adapted from a standard S4 application, which is evident by the holes in the intake runner where an IDI fuel injector would normally reside. This same system is available on the normal S4 and can produce up to 503 horsepower.
Roland has set the development durability goal of 50,000 km for this Clubsport RS4. This means he is not going to release the kit into production until the test car reaches 50,000 trouble free kilometers on the stock engine internals. Currently, the press car has seen roughly 15,000 km, so there is a ways to go. However, press cars tend to see slightly more, ummm, “wear and tear” than the average car so one can rest assured that it has been thoroughly tested and developed under all conditions. We drove this car hard, and it ran well without a hiccup.
Development of MTM’s supercharger system was far from easy. Three important factors contributed to the overall difficulty of the project; size (component packaging), heat, and ease of installation.
Audi has already used up nearly all available space by just fitting a V8 into the A4 chassis. They’ve shortened the engine length as much as possible by using smaller than usual bore-to-bore spacing and fitting the accessory/cam drive to the back of the engine. This didn’t leave Roland much real estate to work with on the front side.
A supercharger setup works by turning an air compressor (blower) mechanically with a belt and pulley system. The extreme revving capability of the RS4 engine means the entire belt drive system must be able to withstand high speed and high torque operation. At full boost, the supercharger can require 50 or more horsepower from the engine to spin itself, which must be transmitted through this belt. Considerable effort went into designing the belt/drive assembly to fit into the small space and function without slippage under all conditions.
The additional heat generated by this setup necessitated the carbon fiber scoop which peeks menacingly from the hood area. MTM also concluded intercooling was vital for safe and consistent power delivery. Trials without intercooling showed that intake air temperatures would climb too high, which in turn would decrease power output as the ECU pulls back ignition timing to compensate. Higher temperatures also increase the likelihood of engine knock, not something welcome to an owner when a $30,000 RS4 engine is in stake. The water-to-air intercooling system taps cleanly into the factory cooling system adding an additional heat exchanger before passing through the supercharger.
“Power is nothing without control”. This cliché statement holds especially true with MTM’s RS4. Simply adding more power to a stock RS4 would result in a less rounded vehicle, perhaps not as effective overall as what originally rolled off the line at quattro GmbH. The remainder of the modifications were therefore designed to make maximum use of the additional power produced by the supercharger. Weight saving measures bring the curb weight of the Clubsport down to a claimed 1660 kg (3650 lbs). This is about 350 lbs less than a US-spec RS4 even while counting larger brakes and additional safety features.