The SSGTi.com Underdrive pulley replaces the stock crankshaft pulley with a lighter weight and smaller diameter pulley, which allows the engine to rev faster and make more power. An average of 1.8 HP is gained from every pound lost off the crank shaft. Our pulley is almost 3 lbs lighter than Suzuki’s. By making the pulley lighter and stronger this places less stress on the engine and lets your Gti make more power. Furthermore since the underdrive pulley has a 20% smaller diameter there is a lower "tangential" velocity than the original pulley given at a constant engine RPM. This means that with the aftermarket pulley, less energy is used to drive the accessories, and hence more power is available at the front wheels. After installation the result is a noticeable increase in horsepower (about 5-7 hp) and unlike most modifications this power is not peak power, but rather power from 1500 rpm through 7500+ rpm. In other words across the entire power band. In this article we will give you a overview on how to install the pulley on a GTi. You can buy this pulley for your GTi/GT from our online Webstore

First off you will have to remove the air hose from the MAF to the throttle body to gain access to the alternator.

  

You will require a 12mm wrench to loosen off the top alternator adjustment bolt. Loosen that bolt off just enough for the alternator to be able to move freely. Some alternators tend to almost seize up in their normal position. You may need a pry bar to move the alternator enough to remove the tension on the alternator belt. With the belt loose remove it and pitch it in the garbage. If your car is equipped with A/C you will have to loosen off the A/C belt and remove it first. Doing this involves usually getting underneath the car but not always.

With the belts removed you will have to raise the car slightly to gain better access underneath the car to remove the splash guard in front of the crank pulley. There are about 6 clips that hold it in place.

With it removed you will need to start removing the bolts that hold the pulley in place. You will need the 5mm Allen socket and a ratchet handle and you will probably have to hold the crank pulley as you loosen the bolts off. You can either block the flywheel with a screw driver from below or have a helper apply the brakes while keeping the car in 5th gear. The bolts will come loose, but just make sure the Allen socket is seated in completely. You will have to do one at a time and use a 17mm open end wrench to turn the engine CLOCKWISE to gain access to the next bolt. Just use the ratchet to get them loose and then remove the bit and use just it to turn them all the way out. There isn't a lot of clearance for a ratchet in there so just take your time.

With all the bolts out it is time to remove the pulley. There are 2 ways of doing this. The first option is to lower the engine a bit. This can be done quite easily but care should be taken. It is a must that the engine is properly supported after it has been lowered. The easiest way to do it, is loosen off the 2 bolts that hold the round engine mount to the bracket that is bolted to the engine itself (Passenger side mount for LHD drive cars). The trick is to loosen them off almost all the way but not quite. You only need to drop the engine maybe 1" but we recommend if you go this route to place a jack under block to support the engine incase you've backed the bolts out a little too far. You might have to play with it a bit to try and get it just low enough. You'll have to pull on it a bit but it will come out. The second way to take out the pulley is remove the 17mm bolt attached to the crank with a low profile socket and wrench. This is the method suggested by Suzuki, but it is also the hardest method out of the 2 techniques, since there is quite a bit of torque on that 17mm bolt. Out of the 2 methods, we suggest going with method #1.

The original heavy pulley has been removed in this picture

Reinstallation is the basically the opposite of the removal except that the new pulley being smaller will slip right in there. If you picked method one above on removing the original pulley it is alot easier to replace the 5 Allen bolts since the engine is a bit lower. Also a good tip is to Coat the inside bore of the new pulley with anti-seize compound and then slide it onto the engine and secure.

1st Picture : New underdrive pulley and stock pulley shown | 2nd Picture : Pulley on the car.
  

When you are tightening down the bolts take care not to really crank them down. They are very small and can snap quite easily. There is tight and then there is too tight. You will also need to get shorter belts for the new pulley. You can get the belts from our web store or from your local parts place. The ALT requires a belt that is 1" shorter than stock (32"). If your car has A/C then you'll need a 29" belt for the A/C compressor.

The intention of this article is to give the reader an idea of what is involved in installing an underdrive crank pulley. It is by no means a complete set of instructions on how to complete a pulley change. The author/SSGTI.com takes no responsibility for damage or loss whatsoever as a result of someone attempting a project like this. Things of this nature are best left to experienced people with the equipment and knowledge to do the job.
Author: B. Faherty