It is essential that you measure the boost pressure of your supercharger at the manifold with an accurate boost gauge. Stock G-60's hit 9 lb of boost (at sea level) just before the rev limiter cuts in. If you can't get 9 lb, you may have a boost leak. I found one at the intercooler. A hose clamp is great for round hoses, but not too good for oval ones. I changed and sealed the oval hose on the intercooler (with silicone seal) before reinstalling the hose clamp. Be careful with silicone in the intake, though, as just a little bit ingested by the engine will contaminate and destroy the oxygen sensor.
There is a special device VW uses to find boost leaks. Chances are that you are no more likely to have this than I was. Without this, you'll have to investigate all connections between the supercharger and the intake manifold (which, without the tool, is what I had to do). Don't forget all vacuum lines coming out of the intake and going to places like the power brake booster and the charcoal canister. Check each hose, one-way check valve, and vacuum diaphragm with your vacuum pump.
I found that sudden pulses of pressure can damage these vacuum diaphragms. Popping back (backfiring) while under boost ruined several of ours, including the fuel pressure regulator, and vacuum modulator inside the computer (available as a separate part for $90 from Bosch).
A common Corrado G-60 problem is low boost, and one surprisingly common reason is damaged intercooler plumbing. We all think of plastic being more or less impervious to acid, but in fact the plastic intercooler plumbing of the Corrado often falls victim to acid damage from the battery. Since the intercooler is in the driver's side front beneath the battery, battery acid frequently damages the plastic plumbing. This common source of a boost leak isn't that easy to find, hidden away under the battery as it is, but there is a relatively simple fix. Eurosport has some "replica" high-flow pulled-mandrel-bent steel intercooler pipes for the Corrado that accurately replace damaged stock units. Just to make sure, I recommend a battery which won't cause acid damage, like the Optima, to make sure the problem doesn't return.
If your oxygen sensor fails and the system goes full rich, chances are you'll experience some popping back as you struggle to keep the engine running. If you can't find any boost leaks, yet you're way short on boost, chances are the seal inside your G-Lader is gone.
This is not an uncommon problem and is as likely to occur on a well maintained stock G60 as one with an aftermarket pulley and chip. Since new G-Laders cost over $2,000, you'd be wise to ship yours off for repair. New Dimensions, here in the US, has a relationship with TEK, the only factory authorized G-Lader rebuilder. It has the parts (seals, bearings, and so on) and the expertise to rebuild your G-charger. As icing on the cake, New Dimensions also offers several stages of performance mods for the G-Laders, designed to make more boost, and sooner. Essentially porting and polishing, these performance mods make a significant difference in performance and are the real secret to G-Lader performance.
Another likely suspect (and extremely common source) for a small to moderate boost leak is the idle stabilizer. To some extent, the leakage of this unit can be at least minimized by turning the tiny Allen screw located in one end. By blowing on the unit, it is possible to adjust the Allen screw for minimum leakage. With age, these valves just wear out.
The best solution, however, is proposed by Neuspeed with it's latest HP kit or the check valve called the Jiro Valve offered by Eurosport. Essentially, the idle stabilizer is vented back into the intake, so the pressure on each side of it is equal when under boost. Leakage doesn't matter then. I fabricated such a part and found it to be an essential mod.
Concerning the G-Lader itself: There are specific rules you must follow to make yours last. First, never let it over rev. The Firehawk race guys blew six superchargers in one season, including one hand-made VW Motorsports model. Just one incident of overreving (generally a missed shift or an early downshift) virtually guaranteed a blown G-Charger. They were often operating with the rev limiter defeated, but even blew a few with the rev limiter operational. Since aftermarket chips can up the rev limit to 7000 rpm, and aftermarket pulleys substantially increase supercharger to engine gear ratio, it's no secret that, at maximum rpm, the design limit of the G-Lader is often dangerously close to being reached.
Fortunately the G-60 engine revs slow at high rpm (from the huge drag imposed by the supercharger). This, along with the rev limiter, pretty much protect you in the event of a missed shift, but offers no protection should you downshift prematurely or into a much lower gear. Even if you don't over rev your G-60, you must take further precautions to make the G-charger last.
First is oil. the G-Lader bearings are under great stress at 15,000 rpm and demand good, fresh oil. I think synthetic is the only way to go in this car. Mobil One, Amsoil, and Redline are my favorites. Owners who don't change their oil regularly have reported losing the bearings (and of course the rest of the G-Lader as well).
One of our project cars lost two superchargers. The other is still on the original at 70,000 miles. The first car probably lost it's first G-Lader due to running it without an air filter (but it sure runs fast like that!) Dust and dirt are simply not tolerated. The second car uses a good filter, like a K&N. Amsoil claimed to have a foam filter that flows about as well as the K&N, but filters small particles much better. I tried it, but the foam material restricted air flow, the Amsoil filter robbed as much horsepower as the Autothority chip added! Eurosport sells the ITG Pro-Filters, which seem to offer the best of both worlds when it comes to filtration and flow. More importantly, Eurosport has a mandrel-bent inlet from the filter to the G-Lader inlet and a fabricated heat shield to keep hot air out of the air inlet. It's an elegant solution to at least part of the "more air flow" problem.