The first generation MINI Cooper S, built between 2001 and 2006, is powered by a supercharger. The supercharger in the early Cooper S provides more oxygen to the motor and, consequently, more fuel. This increase in distribution of oxygen and fuel to the Cooper S’s motor yields higher power output. However, there is still more power attaintable due to MINI aftermarket parts like the reduced-sized supercharger pulleys.
Typically, aftermarket pulleys 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 stock pulley. For instance, a 15% pulley is 15% smaller than the one that comes stock in the MINI. The smaller the pulley, the smaller the belt; and, the smaller the belt, the faster the turbines in the supercharger spin. When the turbines spin faster, more oxygen is supplied to the motor and the motor yields a higher power output. What does this amount to? More torque and horsepower.
In the R53 MINI Cooper S, expect to capture a gain of about 15 HP after installing a 15% pulley. (Remember, the percentage of the pulley does not correspond to the gain in HP – this is just a coincidence.) With the 17% expect a 20 HP boost and, with the 19%, a 25 HP boost. All HP gains vary based on the condition of the MINI and previously-added performance parts.
When considering the cost of an aftermarket pulley – $100 to $150 – and the amount of extra HP gained, it’s one of the most cost-effective upgrades in the R53 MINI aftermarket. MINI performance parts like bulky intercoolers and exhausts cost around a grand 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 a lesser HP gain with various performance parts that are heavier and more expensive. This is why many enthusiasts are quick to make an aftermarket pulley installation their first MINI upgrade.
But which pulley should you buy? The 15%, 17% or 19%?
By looking at the HP gains produced by each pulley, it seems best to go with the 19% for the highest HP gain. The 19% pulley, however, isn’t the most practical. The 19% delivers the most boost, but also delivers the most wear to the vehicle’s internals. The 19% is good for short circuit races or time trials while the 15% is good for endurance, long races and everyday power cravings. Putting this into perspective, the 17% is a compromise between the two. It delivers an increase in HP over the 15%, but causes internals to wear slightly faster. Overall, the 15% is the most recommended pulley for everyday drivers of the R53 MINI Cooper S looking for a substantial power gain.