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 about 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.
Independent review:
Fundamental
physics hasn’t changed much since the days of my high school physics
class. When you attach two pulleys together, changing the ratio of one
pulley changes the amount of work you must put in to “lift” a certain
object a specified distance. Most modern engines employ various
pulleys, driven by belts connected to the crankshaft by a main pulley,
to supply power and drive various accessories on a vehicle. BMW has
designed specific pulleys in the engine compartment to drive the
alternator, water pump, power steering pump, and A/C compressor.
These accessories present a parasitic drag on the engine’s horsepower.
One way to reclaim that hidden horsepower is to replace some of the
pulleys with an “under-drive” pulley. I’m sure we’re all familiar with
the term “over-drive”, a ratio smaller than 1:1 in the gearbox to
achieve higher speed at a given RPM. Under-driving a pulley is the
exact opposite. A larger diameter pulley is used so that the accessory
will make fewer turns for every engine revolution, thus requiring less
work from the engine, but also resulting in less work done by the
accessory.
Installation
UUC’s Ultimate Underdrive Pulley kit comes with a replacement pulley
for the water pump and the power steering pump. It comes with two
aircraft quality machined pulleys anodized in silver or black, along
with a replacement belt. The built quality of the kit is excellent,
with flawless machining on the pulleys and a beautiful design. I
optioned for the black anodized pulley set to blend into the engine
surround. Installation of the kit is about as simple as turning a few
wrenches, especially on cars that does not come with a mechanical
cooling fan. On models that come with the mechanical fan, you will need
the fan clutch removal tool (a long, 32mm/36mm wrench). Other than that
there isn’t really any special tools required to do this job. The bolts
that hold down the water pump pulley are 10mm bolt, and the bolts that
hold down the power steering pump pulley are 13mm. There are some
simple rivets and screws you will need to remove if you intend to
remove the electrical fan, to allow you additional access to the
pulleys, and you will need a 16mm socket/wrench to turn the AC belt
tensioner and a T50 Torx bit to turn the accessory belt tensioner.
Installation is as simple as remove belt, remove pulley, install new
pulley, and install new belt. Entire procedure takes about 1 hour for a
shady tree mechanic, including jacking up the car and all the prep
work. UUC includes a detailed instruction set with pictures and easy to
follow steps, which takes all the guesswork out of a DIY project.
Performance
Well, they say it’s almost impossible to feel any performance
improvement under 10% by the seat of the pants. UUC proclaims a
4hp-11hp increase measured at the drive wheel, which for most modern
BMWs is a less than 10% increase.
Despite the moderate claims, there are tangible benefits to the pulley
kit that you CAN feel. One of the most immediate results of installing
the pulley kit is better engine response to throttle input. As best as
I can describe it, it feels like the engine is “lighter”, or that it’s
got less drag on it. The most obvious evidence of this is when you are
engine-braking. There’s less drag on the engine and it takes longer for
the car to slow-down. I’ve noticed a small increase of about 0.5 miles
to a gallon since my last fill-up. Another benefit seems to be when I’m
executing heel-toe downshifts. Since the engine seems more willing to
rev up, I find it easier to control my blips to match the revs.
Value
This is one of the more affordable and safe modifications you can make
to your engine. Since the UUC kit does not under-drive the main
crankshaft pulley, which acts as the harmonic dampener for the inline 6
engines, and it does not under-drive the alternator, it eliminates two
of the sources for possible problems down the road. Some kits that
under-drives the alternator may result in dropped voltage to drive
in-car electronics, or alternator interference that decreases the
performance of your FM and AM reception. And since the kit is so easy
to install, if you’re familiar with changing the oil in your car and
have the proper tools you should be able to perform this modification
yourself. Best of all, it is certainly one of the most affordable
modifications you can make to your car at this price point.
Conclusion
I’ve now recommended and installed 3 sets of UUC’s Ultimate Underdrive
Pulleys on a few friends’ BMWs, and I have to say this is an excellent
bang for the buck product. Especially for those with 2.5 liter engines,
which suffer from the drag on these various accessories more than the
2.8, 3.0 liter or 3.2 liter engines due to the smaller displacement. If
you have a couple of hundred dollars allocated to modify your car, this
is one of the product you should put very high up on the list of things
to get.
