[wohi]

Hier, was Mini-Tuning Haudegen Randy Webb zum Thema Leistungssteigerung schreibt - passt ganz gut zu dem Thema:

The biggest bang for buck is the supercharger reduction pulley. What does this actually do though? By using a smaller pulley, the supercharger rotors are spinning faster. This creates more boost (pressure), but it also creates more heat - that bothersome physics thing again. All superchargers are designed to operate in a certain window, a "sweet spot" where boost can be created as thermally efficient as possible. With our Eaton M45 based Roots type supercharger, a 15% smaller than stock supercharger pulley is the most efficient at all RPMs. Since the car will see track time, where the full rev range will be exploited, this is the size pulley I recommend. We have also seen drive belt issues on cars that visit the track with pulleys smaller than the "15%" pulleys, which reinforces my selection for this application. The pulley we use is a stainless steel unit which has a similar thermal expansion rate to the shaft of the supercharger. Considering how small the radius of the pulley is (less than 1.25"), the additional weight of this rotational mass is more than worth it for the piece of mind afforded by not only the thermal expansion properties, but by the anti-corrosion properties as well. There are no measurable power differences in 15% pulleys of different materials. Typical gains from the 15% pulley are in the 15-20 horsepower range. Our pulley is $120-129.

The next step in our quest for more power is the cold air intake (CAI). To gain power, we want as much potential energy in the combustion chamber as possible. One of the main ways to achieve that goal is by maximizing density. Density is directly proportional to pressure, and indirectly proportional to temperature - in other words, as pressure goes up, so does density, but as temperature goes up, density goes down. We have increased pressure with our supercharger pulley, and now we can do two things with a CAI: decrease temperature, and increase flow. This generates the second biggest bang for buck. We do this by increasing the surface area of the filter, isolating the filter from the heat of the engine, and gaining access to more colder cowl area intake air - the duct just below the windshield wiper. Webb Motorsports uses an intake with a high flow foam filter element, which has proven itself the most durable and highest flowing after four years of track testing, and by removing the cowl partition and creating a new firewall with the airbox itself. Gains are in the 7-10 horsepower range. Our intake is $200-260.

These two upgrades will get you to 90% of the factory John Cooper Works power level, at a fraction of the cost. It is also reliable - we have over 1,000 customers running this set up, a few with over 100,000 miles. Of course, there are a couple more modifications you can make to go beyond the Works package - an ECU, cat-back exhaust, etc., but we want to upgrade other areas of the car to go with our new found power and remain within a reasonable budget. There will always be birthdays and holidays down the road!

You may notice I mention the ECU as a performance upgrade, but do not initially recommend it as a necessary safety upgrade in conjunction with the supercharger pulley. The MINI uses a Siemens EMS 2000 ECU to monitor and meter air/fuel ratios, ignition timing and a host of other functions. This is a very advanced system. Instead of using a mass air flow sensor (MAF) for metering fuel, which is upstream of most density and flow changes, the EMS 2000 uses a temperature and manifold air pressure sensor (T/MAP) downstream of the entire air intake path. This is true density and because of the location after the CAI, throttle body, supercharger and intercooler, the ECU is able to meter fuel accurately and safely even after our upgrades. Bottom line to this important sidebar: an ECU upgrade is nice to have, not need to have.