UUC Motorwerks E46 330/328/325/323 Ultimate Under Drive Pulley Set - Parts in Detail

It takes more to create an underdrive pulley system than just oversize pulleys and a longer belt. The engineering process begins with an in-depth examination of:

1) Each of the pulley-driven components under the hood.

2) Why or even if that component should be underdriven.

Let's take a look:



Alternator There is a lot of speculation about the operation of the charging system in your BMW. Let's skip straight to the facts: an alternator does not constantly produce current. Like the A/C compressor, it cycles on and off as demand goes up and down. The battery buffers it from the electrical demands of the car, and it only works enough to maintain system voltage. Underdriving the alternator would have ramifications ranging from dim lights at idle, to insufficient charging ability, and potentially as far as damage to your BMW's voltage-sensitive components. It may also cause inconveniences in the operation of your aftermarket electronic devices and ICE. For this reason, UUC has deemed that any gains made with a replacement alternator pulley will not be due to reducing its RPM.  Alternator output is not affected.
Power Steering The hydraulic power for the steering is provided by a rotary-vane pump, which is a type of positive-displacement pump. By definition, positive-displacement pumps displace a known quantity of liquid with each revolution of the pumping elements. For this application, the pump has been designed to provide adequate flow when the engine is idling. As a result, the pump moves much more fluid than necessary when the engine is running at faster speeds. Underdriving it by a reasonable percentage will yield no perceptible change in power steering assist, but will free up power that is lost to shaft vibration and fluid cavitation.
Water pump The fluid drag of a centrifugal pump, such as the water pump, does not increase linearly with RPM. Rather, the load will increase by the square of the pump's rotational speed. This means that the pump's power consumption will rise at a more rapid rate than engine speed. The more you decrease the pump's RPM, the gains also decrease. UUC has struck the balance of power gain and pump efficiency with our underdrive pulley for the water pump.
Air conditioning The operation of the A/C compressor is cyclic. Depending on various RPM and temperature conditions, it will cycle on and off with varying frequency. Either way, the same amount of work is done to cool the car's interior. Underdriving the A/C compressor would not yield any gains, or any discomforts. UUC has chosen not to supply an underdrive pulley for the compressor, but we do include a new OEM belt to make your installation as smooth as possible.
Crank pulley Also called the "main pulley", this drives all the other pulleys.  By changing the size of just this pulley, all the other pulleys would effectively be underdriven.  While this would seem like a simpler method, there are two significant problems: As explained above, not every accessory reacts well to being underdriven.  Additionally, the crankshaft pulley is also the the tuned harmonic damper. The crankshaft on your inline six is subject to a wide variety of vibrations and harmonic phenomenon, and the damper incorporates an elastomeric component to protect the crankshaft from harmful effects of these forces.  The risk of removing the harmonic damper is catastrophic failure of the crankshaft.


Clear anodized or optional "stealth black"

From Concept to Reality...

For the construction of the Ultimate Underdrive Pulleys, 6061-T6 heat-treated aluminum was the best choice for several reasons. Due to its density and strength characteristics, mass differences between the OE accessory pulleys and the UUDP are optimized while retaining factory-like longevity. The precision fit of the Ultimate Underdrive Pulleys begins on a CNC lathe, and continues in a multi-axis mill where the  power swirls are added. 

Are there pulleys available that underdrive more than UUC's?

Probably. Why would you want them? Is your BMW a race car, with an unlimited budget, dedicated to the sole purpose of shaving lap times? 

Most of you are probably like us - you have a BMW that wasn't cheap to buy, isn't cheap to fix, and is more to you than "just a car". There is a limit to how much you can underdrive your accessories before cooling capacity, alternator output, and power steering pump life are adversely affected.

The question you probably meant to ask was are there kits that can free up more power than the UUC?  Maybe.  But at what price? To repeat, there is a limit to how much you can underdrive your accessories before cooling capacity, alternator output, and power steering pump life are adversely affected. Do you want to push that limit? For an extra 1 or 2 or 3 hp in your daily driver or weekend fun car? 

From UUC's point of view for street cars, there's no stopwatch worth ruining your engine for.

One of the other reasons for choosing 6061-T6 aluminum for the construction of the Ultimate Underdrive Pulleys is the ease with which this material can be anodized. UUC's hard anodized finish is not only cool to look at, it helps eliminate belt slippage and boasts improved wear characteristics over the life of the pulleys. And with our optional black anodizing* for a stealthy appearance, no one needs to know about this upgrade but you.

For the smoothest installation possible UUC includes a new, high quality, correct-length accessory belt.

The Finished Product is a set of pulleys that fits like factory, accepts a commonly available belt for easy long-term ownership, and boasts impressive gains for not a lot of money! Now that's what we call Ultimate!

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