What is a 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 we don't make a pulley kit for them. The pulley kits we do make are for engines that do not rely on the balancer to any significant degree.

Isn't there a loss of torque associated with fitting lightweight pulleys, since the flywheel effect is lost?

No. In early days it was common to fit large heavy flywheels to increase torque, which to a certain extent does work, but it is important to look at the context of the application. A heavy weight acting as a flywheel on the crankshaft has a greater resistance to a change in rotational velocity, which is termed inertia. The term "resistance to change in rotational velocity" applies to both acceleration and deceleration, so a heavy flywheel or pulley does oppose deceleration in situations such as towing caravans up a hill, but it will also oppose fast acceleration.

It is easiest to think of inertia as an energy reservoir, and the laws of physics state that you can only get out the same amount of energy as you put in (actually in the real world it is often less due to irreversible losses). So an engine needs to put in a significant amount of energy to accelerate a heavy pulley before any useful torque can be extracted from it. Don't forget that when the engine is at low RPM before the turbo spools up, it is only making about 20% of its maximum power, and in this situation the amount of energy required to accelerate the pulley becomes a much larger percentage of the available power. 
If you were to measure an engine's torque whilst applying a load high enough to cause the revs to drop, then a heavy pulley will show a higher figure. But if you measure the torque whilst the revs are increasing, the lighter pulley will come out on top. If you can think of a case when your 200SX or WRX is at full throttle and the revs are DROPPING, then it means your engine is probably running on 1 cylinder. In a high performance engine the emphasis is on acceleration, not momentum.

How much lower is a GFB shifter than the factory one?

The GFB Short Shifter is the same height as the factory shifter, it is the actual distance that the gear stick moves between gears that is reduced.

Are there any problems associated with under driving the alternator and power steering pump when using a Power-up Pulley Kit?

No, the ratios are only reduced by about 15% on the alternator, and 20% on the others. This means that you get full charge at 1000 RPM instead of 850 RPM which will only cause problems if you plan to drive your car at idle for long periods of time with the fan, high beams, air conditioning, rear demister and stereo full blast.

The reason for under-driving is that from the factory the accessories (alternator, A/C, power steering) are designed to run at almost 100% at or near idle, so at high RPM they are causing excessive and unnecessary drag. Reducing the drive ratio by 15% doesn't have a large impact at idle, but at say 6000 RPM, 15% becomes a much larger proportion and the reduction in drag is much more noticeable.

I've heard bad stories of gearbox damage from using a short shifter - is this true?

Absolutely not!

We've heard this concern many times, often from 'internet experts', and surprisingly even from so-called 'performance mechanics'. Read on, and you can smile to yourself knowing that when someone claims to have damaged their gearbox because of a short shifter, it's more likely they are in fact a sloppy driver. 

Here's the hard truth - a gearstick is simply a lever, connecting the driver's hand to the gearbox. Any wear or damage is proportional only to the way in which it is used (or abused!), no if's, but's or maybe's about it. If you shift hard and fast (or time the clutch poorly), the synchros will wear out faster regardless of what type of shifter you have.

The GFB Short Shifter reduces the travel of the gearstick - if you reduce the throw by 20%, there is a 20% increase in the effort required to shift gears - this is the very basic principle of levers. Whilst this increase in shift effort may give the feeling that you are stressing the ‘box more by having to push the stick harder, you are in fact exerting the same shifting force to the gearbox. Additionally, the reduced throw may falsely lead the unsympathetic driver to believe faster shifts can be performed - you can only shift as fast as the synchros will allow.