BruceWarne

I've been thinking about getting some of these (from GFB). Seem a nice way of freeing up some extra power without increasing stress on engine. Anyone have any experience?

Looks like the main issue is dampening. Does anyone know of any failures caused by using these parts?

From the GFB web site:

"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"

Scott W

Hi Bruce,

I've just fitted these to my car, and the difference is definitely noticeable. I researched long and hard in to the downsides, and from the findings I came across, there are a few things that could happen, but to date none of these have happened on the cars they've been fitted to.

I know Rich Wild has them fitted, so hopefully he'll post up here, as he certainly put my mind to rest on them!

Sorry I can't help anymore, as I've only had them on a week!

harvey

iTrader: (48)

Bob Rawle (465 bhp) has a set from Roger Clark Motorsport.

RICH WILD

Hi,

I've had them on my cars for over 12 months and can report no problems.

As Scott says, you can definately notice the difference to throttle response and engine braking.

I reckon they are worthwhile.

Cheers

Rich