The first generation of the MINI Cooper S, built between 2001 and 2006, is powered by a supercharger. The supercharger on early Cooper S’s provides more oxygen to the engine and consequently more fuel. This increased delivery of oxygen and fuel to the Cooper S’s engine produces higher power output. However, more power can still be made thanks to MINI aftermarket parts like the undersized supercharger pulleys.
Aftermarket pulleys typically come in three different styles: 15%, 17%, and 19%. What do these percentages mean? They simply refer to the size difference between the aftermarket and the original pulley. For example, a 15% pulley is 15% smaller than the one that comes standard on the MINI. The smaller the pulley, the smaller the belt; and, the smaller the belt, the faster the supercharger turbines spin. When the turbines spin faster, more oxygen is supplied to the engine and the engine produces a higher power output. What does this amount to? More torque and horsepower.
On the R53 MINI Cooper S, expect to capture a gain of about 15 HP after installing a 15% pulley. (Remember, pulley percentage does not correspond to HP gain, this is just a coincidence.) At 17% expect a 20 HP increase and at 19% expect a 25 HP increase. All HP gains vary depending on the condition of the MINI and previously added performance parts.
When you consider the cost of an aftermarket pulley ($100 to $150) and the amount of extra HP gained, it’s one of the most cost effective aftermarket upgrades to the MINI R53. MINI performance parts like bulky intercoolers and exhausts are around a thousand bucks and don’t offer the HP boosts that performance pulleys do. In essence, you get an additional 15-25 HP with a two-pound pulley, and less HP gain with various high-performance parts that are heavier and more expensive. This is why many enthusiasts rush to do an aftermarket pulley installation as their first MINI upgrade.
But which pulley should you buy? 15%, 17% or 19%?
Looking at the HP gains produced by each pulley, it seems best to choose 19% for the highest HP gain. The 19% pulley, however, is not the most practical. 19% offer the most boost, but also cause the most wear on the internal parts of the vehicle. 19% is good for short circuit races or time trials, while 15% is good for endurance, long runs, and everyday power cravings. Putting this in perspective, 17% is a compromise between the two. Offers an increase in HP over 15%, but causes internal parts to wear out a bit faster. In general, the 15% pulley is most recommended for everyday R53 MINI Cooper S drivers looking for a substantial power gain.