Replacement accessory
pulleys for water pump and power steering pump that use less engine
power. Kit includes new accessory belt.
AVAILABLE
APPLICATIONS:
UUC Motorwerks
Ultimate Under Drive Pulley Set
When you bought your BMW,
you paid for a lot of horses... but are some
of them stuck in the corral?
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 water
pump, power steering pump, and alternator.
All
of these use horsepower, horsepower that is lost. Power that could
be making the car faster.
Real-world
gains measured at the wheels, 11hp in this example.
Each accessory uses rotary
power - each accessory is turned to perform
it's function, whether it's an electrical component (the alternator) or
a fluid displacing component (the water pump and power steering pump).
They all have a pulley which takes power from the crankshaft pulley via
a 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 big
safety margin built into many systems of a BMW, especially in the
accessories.
Driving
these accessories at higher rpm is a waste of energy, running
it at a much higher rate than it needs to for optimum effectiveness.
This is energy which could be put toward acceleration instead. For a
specific example, the BMW water pump loses efficiency at high rpm
as the water just cavitates (makes bubbles) instead of flowing
faster. Slowing down the water pump actually makes it more
effective, especially for sustained high-rpm use.
What's an
underdrive pulley?
An underdrive pulley is a
replacement accessory pulley that bolts up
the same as stock, but has a different size (ratio) and material
specifications intended to free up lost horsepower. By increasing the
diameter of each accessory pulley, the speed at which the accessories
are turning relative to engine RPM decreases.
Does this
actually make horsepower?
Underdriving the
accessories does not add power to the engine, it frees
up the power that is normally wasted on overdriven accessories. The
theory is that a larger pulley will drive the accessories slower thus
reducing their parasitic horsepower loss. No more power total, but more
power sent to the wheels. As an additional benefit, the reduction in
wear (less usage) on the accessories due to the lower duty cycles can
extend the life of these parts.
However,
a look at each pulley-driven system under the hood will tell
you 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 drive
pulley, one is electrical (the alternator) and two are fluid pumps (the
water pump and the power steering pump). The fourth is a compressor
(the air conditioning unit).
UUC
Motorwerks Ultimate Underdrive Pulley set provides replacement
pulleys for the water pump, power and steering pump. We do not provide
an alternator pulley because, due to the alternator's voltage
regulator, an underdriven alternator has no power gains.
What abut the
weight?
WARNING: Some companies
have been marketing replicas of UUC's original
pulley design, but advertising them as superior due to "light weight".
This clearly shows these replica manufacturers do not have an
understanding of the underdrive concept... weight reduction is not a
factor in producing power with underdrive pulleys. The gain comes from
reducing the accessory speed, not from less rotating mass.
While
some pulley advertisers do advertise "lightest weight", we feel
that to be somewhat deceptive... in our extensive testing, we have
proven that the actual weight of the pulleys is not a factor in
increasing power gains whatsoever. Each pulley itself weighs just a few
ounces. Shaving off a small amount of additional aluminum will
not make one single bit of measurable power. Weight savings in a BMW
that are important are in the much larger rotating components such as a
lightened flywheel or lighter road wheels.
Why does UUC
offer accessories pulleys instead of a replacement crankshaft pulley?
At UUC Motorwerks, our goal
is improvement of the total performance
envelope. We don't want to provide a product that is only appropriate
to some cars and some circumstances.
By
using an underdrive system based on the accessory pulleys, UUC has
the ability to fine-tune the specs of each pulley. None of the
accessories on your car have identical operational parameters, why
should the pulleys that drive them?
The
practice of removing your engine's crankshaft pulley in order to
replace it with one of a smaller diameter does have a place in the
performance tuning dictionary. However, it is important to note that
the primary benefits from this modification are due to the decreased
weight of the replacement crankshaft pulley. Regarding the underdrive
effect, all the accessories see the same change in RPM - no fine-tuning
available.
The
price for this gain is the loss of the tuned elastomeric harmonic
damper. The crankshaft on your inline six is subject to a wide variety
of vibrations and harmonic phenomenon. Could UUC have designed a
replacement crankshaft pulley to our satisfaction? Absolutely. But then
we'd have no way to recommend one of our favorite performance
modifications, the lightweight flywheelylish and functional, our
solid stainless steel shift knobs improve shifting feel and positive
gear engagement.