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This is a 3 pc. non-underdrive kit that will help improve acceleration (same
dimensions as OE parts so you use the original belts).
Why no Harmonic Balancer?
A better name for a harmonic balancer would be "torsional dampener" since its
main task is to absorb the rotational pulses inflicted on the crankshaft by the
pistons. Most often it is incorporated into the crank pulley by attaching the
outer belt drive ring to the inner by means of vulcanized rubber. At the right
RPM, it is possible for a resonant frequency to be set up torsionally on the
crankshaft. Resonant frequency occurs when the pulses of the engine correspond
with the natural frequency of the crankshaft and it ancillary components.
However, since factory pulleys are often comparatively heavy (reasons for this
are described later) it is actually the large mass (and therefore inertia) of
the factory harmonic balancer and flywheel that will help to excite this natural
frequency. So by dramatically reducing the weight and inertia of the crank
pulley, the natural frequency of the crankshaft is shifted and its ability to
self-excite is greatly reduced. So in fact it is the harmonic balancer's own
weight that necessitates the dampening, and since the weight of a GFB crank
pulley is typically about 20% of the factory component it cannot supply an
exciting force significant enough to damage the crankshaft.
An opinion often expressed is "if the manufacturer put it there, it must be
there for a reason". However, if you look at it from the car manufacturer's
point of view, casting pulleys from steel is very cheap and easy, because they
can be produced in large numbers and there is no waste (as opposed to machining
them from billet). But because the resulting pulley weighs significantly more
than one made from aluminium alloy, it requires dampening.
Manufacturers will always build cars (even high performance cars) to suit the
widest possible selection of driving scenarios and drivers, which means there
are always compromises. The weight of the flywheel and pulley also affect how
fast the revs drop between gear shifts, and a production car is designed to only
allow the revs to drop fast enough for average shifts. If you hurry the shift
the revs will be too high for the next gear, resulting in a sharp jerk as the
momentum of the engine transmits through the drivetrain. Reducing the engines'
inertia with a lightweight pulley kit allows faster and smoother shifting.
When looking at high performance engines such as those found in Honda VTEC
equipped cars and the S2000, it is obvious that manufacturers do understand the
benefits of reducing engine inertia, and have utilized lightweight pulleys to
help the power output and responsiveness without the use of a harmonic balancer.
However, this is not the case for all engines, many of them do require the use
of the harmonic balancer to prevent failure. Skylines with the RB20, 25 and 26
are a good example of this, which is why GFB does not make a pulley kit for them.
The pulley kits they do make are for engines that do not rely on the balancer to
any significant degree.
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