...the Corrado finally satisfied the hard-core gear heads with a mysterious never-before-seen supercharger known as the "G-ladder".
The G-ladder (also known as the G-Charger) is based on a Scroll-type supercharger which was invented in 1905 by L. Creux of France. Later developed for VW by Dr. Klaus-Dieter Emmenthal, the modern G-Charger is quite a technological marvel.
Functionally it has more in common with Felix Wankel's unique rotary engine than it does with any traditional centrifugal or Rootes-type positive-displacement supercharger. From the outside the G-ladder looks almost conventional in design. Peer inside, however, and things look different--very different.
In the scope of this article I'll answer a few questions about the G-Charger: How does it work? How does it break? How do you fix it? How do you upgrade it?...
...Like all superchargers, the G-Charger works like a belt driven air pump, pressurizing the engine's intake manifold. In the Corrado's case, that's with nearly 9 lb of boost. There are five major components in this supercharger: two eccentric shafts, two spiral "G" shaped housings, and one spiral shaped magnesium-alloy displacer unit. One of the two eccentric shafts drives and supports the displacer while the other is used to keep the displacer from rotating within the housing. A toothed belt "times" the movement of the displacer and ensures that the two shafts rotate in phase.
As the shafts rotate, the displacer (shaped like a "G") internally compresses the air as it moves in a circular motion. To truly examine the dynamics behind the G-Charger let's examine a simplified, cross-sectional diagram at each phase of operation.
Phase 1: The inner chamber draws air from the supercharger's inlet while the air in the outer chamber is compressed.
Phase 2: After 90 degrees of movement, the inner chamber is partly collapsed, nearly sealing off the intake air. In the outer chamber, the compressed air is partly collapsed, nearly sealing off the intake air. In the outer chamber, the compressed air is exhausted from the supercharger's outlet and pressurizes the engine's intake tract.
Phase 3: After 180 degrees of movement, the inner chamber is completely sealed, fully compressing the trapped air. The outer chamber, on the other hand, just begins the intake phase of the entire process.
Phase 4: After 270 degrees of movement, the compressed air in the inner chamber is expelled from the supercharger's outlet and into the engine's intake tract. The outer chamber, like the inner chamber in phase 2, is almost sealed and begins to pressurize the intake air. The entire process is repeated.
This brings us to our second question: "What can go wrong?" According to TEC the G-Charger is a relatively reliable device. However, when problems arise, things can quickly become serious. For example the eccentric shaft bearings often become loose over time. Once they loosen, the displacer can suffer serious damage as it collides with the housing's internal spiral-shaped walls. In fact in some cases, the walls themselves have been known to completely crumble. Finally, seal life is an even more important issue. The seals along the edge of the G-scroll can wear with age, reducing boost and thus performance.
Another catastrophic failure can occur if the toothed belt, which connects the two shafts, snaps. In this unfortunate situation, the displacer would spin out of control and could cause serious damage to the blower's internal chambers.
Tim Hildarbrand (owner of New Dimensions) says "Having the G-Charger rebuilt at the 60-80,000 mi. mark can usually prevent a catastrophic failure down the road. Replacing the belt, and other parts is quite a bit cheaper than replacing a housing that's been thrashed by a failed belt."
U.S. driving conditions are pretty low key compared to Germany, and our cars don't often see flat-out, high rpm time. Even a pulley to increase G-charger speed and boost doesn't seem to hasten the failure of the supercharger. Still, all of the failure modes tend to occur with time, after the car has accumulated a good many miles. In fact you can rest assured that any G-charger will eventually suffer one of these failure modes. They are after all, only mechanical devices, subject to wear.
So how do you repair a damaged G-ladder? Before TEC began rebuilding G-chargers, the only alternative was to replace it with a brand new unit directly from Volkswagen. At $2,200 a pop, this approach was anything but cost effective.
Once Volkswagen granted TEC the official (and legal) rights to stockpile spare parts, a new window of opportunities opened for G-charger owners. Instead of sacrificing large wads of cash and waiting weeks for a new, factory fresh supercharger, one could now have their aged and weathered G-charger completely rebuilt, in a timely fashion, for a fraction of the cost. New Dimensions charges between $700 and $900 for a standard stock rebuild, a real bargain compared to that $2,200 bill from Volkswagen.
The first stage of reconstruction involves a complete dismantling of the entire G-charger. Once disassembled, all components are carefully examined for defects and signs of premature wear. All damaged parts are removed and replaced. Then the blower is reassembled with new seals and an upgraded full metal bearing assembly (replacing the inexpensive and unreliable plastic bearings that came on earlier models). Once assembled the G-charger is thoroughly tested before it is deemed ready for installation.
Finally, for those of us looking to safely squeeze more output from their blowers, New Dimensions offers a comprehensive line of TEC G-charger upgrades. The first upgrade stage, referred to as Mod1, involves coating the spiral shaped displacer with a proprietary creamy "goop". This unique coating improves the G-charger's effeciency and spool-up response by providing a tight seal between the displacer and the housing's internal chambers.
Offering additional performance, Mod 2 shaves and smoothens the G-ladder's outlet ports for increased airflow and further improved spool-up time. The next stage Mod 2RS, involves additional porting to the G-charger's inlet passages. The final modification Mod GT-1, increases the diameter of the inlet passage and includes an air filter housing adapter. The free-flowing intake increases boost pressures an additional 2 psi, all with no changes in pulley diameter or rotational speeds. The mods just make the G-charger work more effeciently. TEC also offers a twin belt option to protect against belt fractures.
New Demensions No longer does G-Ladder rebuilds. Current choices are listed below in no particular order. Some will sell parts for Do it Yourselfers.