Replacement accessory pulleys for water pump and power steering pumpthat use less engine power. Kit includes new accessory belt.

PLEASE NOTE: This partnumber is suitable ONLY for 1995-1999 E36 M3.

UUC Motorwerks Ultimate Under Drive Pulley Set

When you bought your BMW, you paid for a lot of horses... but are someof them stuck in the corral?Take back that lost horsepower!

A car's engine does many things other than just making the car move.Power is used to run the various accessories... things like the waterpump, power steering pump, and alternator.All of these use horsepower, horsepower that is lost. Power that couldbe making the car faster.Each accessory uses rotary power - each accessory is turned to performit's function, whether it's an electrical component (the alternator) ora fluid displacing component (the water pump and power steering pump).

They all have a pulley which takes power from the crankshaft pulley viaa belt.Some of the engine accessories take more power than they really need,dramatically affecting engine performance.Like an overprotective parent setting a curfew, there is a very bigsafety margin built into many systems of a BMW, especially in theaccessories.Driving these accessories at higher rpm is a waste of energy, runningit at a much higher rate than it needs to for optimum effectiveness.This is energy which could be put toward acceleration instead.What's an underdrive pulley?An underdrive pulley is a replacement accessory pulley that bolts upthe same as stock, but has a different size (ratio) and materialspecifications intended to free up lost horsepower.

By increasing the diameter of each accessory pulley, the speed at whichthe accessories are turning relative to engine RPM decreases.Does this actually make horsepower?Underdriving the accessories does not add power to the engine, it freesup the power that is normally wasted on overdriven accessories. Thetheory is that a larger pulley will drive the accessories slower thusreducing their parasitic horsepower loss. No more power total, but morepower sent to the wheels. As an additional benefit, the reduction inwear (less usage) on the accessories due to the lower duty cycles canextend the life of these parts.However, a look at each pulley-driven system under the hood will tellyou why it isn't as simple as "just a bigger pulley".

Which accessories can I underdrive?

Of the four accessories that can be underdriven with a larger drivepulley, one is electrical (the alternator) and two are fluid pumps (thewater pump and the power steering pump). The fourth is a compressor(the air conditioning unit).UUC Motorwerks Ultimate Underdrive Pulley set provides replacementpulleys for the water pump, power and steering pump. Please see the"Technical Details" page for more information.

What abut the weight?

WARNING:Some companies have been marketing replicas of UUC's original pulleydesign, but advertising them as superior due to "light weight". Thisclearly shows these replica manufacturers do not have an understandingof the underdrive concept... weight reduction is not a factor inproducing power with underdrive pulleys... the gain comes from reducingthe accessory speed, not from less rotating mass.While some pulley advertisers do advertise "lightest weight", we feelthat to be somewhat deceptive... in our extensive testing, we haveproven that the actual weight of the pulleys is not a factor inincreasing power gains whatsoever. Each pulley itself weighs just a fewounces... shaving off a small amount of additional aluminum will notmake one single bit of measurable power. Weight savings in a BMW thatare important are in the much larger rotating components such as alightened flywheel or lighter road wheels.

Why does UUC offer accessories pulleys instead of a replacementcrankshaft pulley?

At UUC Motorwerks, our goal is improvement of the total performanceenvelope. We don't want to provide a product that is only appropriateto some cars and some circumstances.By using an underdrive system based on the accessory pulleys, UUC hasthe ability to fine-tune the specs of each pulley. None of theaccessories on your car have identical operational parameters, whyshould the pulleys that drive them?The practice of removing your engine's crankshaft pulley in order toreplace it with one of a smaller diameter does have a place in theperformance tuning dictionary. However, it is important to note thatthe primary benefits from this modification are due to the decreasedweight of the replacement crankshaft pulley. Regarding the underdriveeffect, all the accessories see the same change in RPM - no fine-tuningavailable.The price for this gain is the loss of the tuned elastomeric harmonicdamper. The crankshaft on your inline six is subject to a wide varietyof vibrations and harmonic phenomenon. Could UUC have designed areplacement crankshaft pulley to our satisfaction? Absolutely. But thenwe'd have no way to recommend one of our favorite performancemodifications, the lightweight flywheel!