VAC Race underdrive pulleys on E46 M3 CSL

I am trying to get a bit of extra speed from the CSL without causing any issues and the underdrive pulley mod always seemed to make sense.

The idea is simple.
Underdrive the water pump and the power steering pump.
Less rpms on both water pump and power steering pump.
Engine cooling should not be affected as the water will have more time to cool down in the radiator and the tuners claim there is temperature decrease in the power steering circuit.


I ordered a set of VAC Ultralight pulleys from MS Motorsport.
VAC (as other tuners) claim 8hp gain throughout the powerband.
They come with the longer belt.


Here are the photos

The new VAC pulleys. Excellent build quality.



The OEM pulleys. Also made from aluminium.


VAC water pump pulley. 137mm diameter. Weight 214g


OEM water pump pulley. 116mm diameter. Weight 211g


VAC power steering pulley. 147mm diameter. Weight 304g.


OEM power steering pulley. 121mm diameter. Weight 153g.


The steering wheel now feels a bit stiffer, nothing too dramatic. I like it.


Now the performance results part.
I made the tests with the exact same conditions (temperature / wind), in the same performance track using my RaceChrono laptiming software (and 10Hz GPS).
Weight of the car was exactly the same and I used only 3rd gear to eliminate differences from gear changes.


Speed from-to (km/h) -> Before (secs) / After (secs)

60-130 -> 5.7 / 5.6
60-150 -> 7.5 / 7.3
100-150 -> 4.3 / 4.1
130-150 -> 1.8 / 1.7


The car is up to 200ms faster in acceleration.
This is a significant improvement (same effect as reducing 32kgs from the CSL).
The pulleys definitely improve the performance and in my opinion they cost very little considering the gains !