Our specially designed and engineered S65 underdrive pulley kit is a great addition to the M3. This is done by improving power through reducing parasitic drag on the engine from slowing the speed of the alternator, water pump and AC compressor components. Hp Gains are approx 10-20hp depending on condition of car, climate, and other performance products. Unlike most other S65 underdrive pulley setups we supply the ESS version with a correct, custom made double sided drive belt where required.
For maximum performance we also suggest pairing our full exhaust system with our specially designed performance software
-CNC hard anodized S65 crank pulley. Precise and measured belt groves and bolt holes.
-Single/ double-sided power steering & AC belt
NOTE: BMW changed the Accessory belt configuration from a single-sided (power steering & AC) belt to a double-sided belt for the E9X M3 that were produced after May 2008.
2007-5/08 production date has single-sided power steering & AC belt.
6/08-2013 production date has double-sided power steering & AC belt.
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I think this upgrade is the best bang for your buck! Easy install with 2 people and I can definitely feel the difference with the power now. 1st gear torque pulls hard, gears 3,4 and 5 will suck me back into the seat! This should be the first engine mod anyone does!