How much extra boost can I run when using a GFB boost controller?

It is very important to be sensible when raising the boost limit on turbocharged cars. Power is directly related to the amount of air and fuel that makes it to the engine cylinders, but lifting the boost level is only one way of doing this. While in most cases it is quite safe to increase the boost by about 10-20%, keep in mind that every component in an engine comes from the factory designed to operate most efficiently at the level it leaves the factory at. If you intend to raise the boost to any more than 20% above factory, you will need to check things like fuel delivery, the intercooler, ignition timing, etc to ensure that they are capable of supporting the increase in power. It is also important to realise the mechanical limits of components, a good example being the ceramic turbine wheels in the turbos found in Skylines, which will take no more than about 14psi without losing blades.

A GFB boost controller will give you the added benefit of not only being able to adjust the peak boost level, but in most cases will bring the boost on earlier, resulting in more power throughout the rev range.

To get the most out of the extra boost it is best to ensure that the engine can breathe properly. A good exhaust is the first place to start. Then follow the inlet tract all the way to the engine, looking for restrictions in the form of resonators, sharp bends or reductions in diameter. Manufacturers will often purposely build in such restrictions to muffle intake noise or prevent overboosting. Removing airflow restrictions means the turbo doesn't have to work as hard to get the boost to the engine.

Why does the boost in my car tend to taper off with increased boost at high RPM?

This is a sign that your turbo system is nearing the limit of its efficiency. Most factory turbos have small turbine housings to reduce lag, but the problem is at high RPM it can cause a large enough restriction to push the wastegate open as the revs increase, often referred to as wastegate creep.

This can also be caused by restrictions in the factory turbo compressor inlet and outlet pipes that also contribute to tapering boost levels, such as convoluted hose sections. The boost controller usually gets its boost signal from directly after the turbo, so the boost at this point is often likely to hold steady. However, restrictions further downstream (corrugated pipes, small intercooler, sharp bends or reductions in diameter) will cause a pressure drop at elevated RPM, particularly if the car is modified and making more power than factory.

It is also important to realise that in stock or mildly modified engines it is probably much safer to drop the boost level a little towards redline. The inertial loads on the reciprocating components increase exponentially with RPM, which is why you will often see the factory ECU drop a few psi near redline. Generally this will occur on cars with small factory turbos, and it is probably in the best interests of the health of the turbo for this to happen unless your engine is built to handle it.

Do I need different belts for the pulley kit?

Yes, however the required belts for the WRX kits are included. All other kits list the correct sizes required.

Is there a dyno graph of the Pulley Kit on the WRX?

Yes, we tested an MY97 WRX on the dyno with and without the kit, and you can see that the chart shows significant gains at the bottom and the top of the rev range. The reduction in rotating inertia (we've removed about 2kg by using 6061 T6 aluminium billet) means that the engine can accelerate much quicker during the times it is making very little power before the turbo spools up. The result is better driveability off-boost and better acceleration, which is especially useful for those with large turbos that only make power in the upper rev range. The smaller size of the crank pulley under-drives the power robbing accessories so that the upper end of the rev range is less burdened, while still allowing them to operate properly.

It is difficult to show the true benefit of the kit on the dyno, since the pulleys reduce INERTIA, which by definition is an object's resistance to acceleration. This means that the benefit only comes when the engine is accelerating, much like removing weight from your car. On a dyno the revs are brought up relatively slowly, and the difference is still noticeable. So on the road, a bigger gain is noticed when you accelerate quickly.

When using a GFB Power Up Pulley Kit, is there any problem with the removal of the harmonic balancer?

Since the crank pulley in our Power-Up Pulley Kit replaces the factory harmonic balancer, people often express concern for the effect that this will have. It is important to understand the task of a harmonic balancer and why they are fitted to explain the effects of fitting a lightweight pulley.