The stock exhaust on the Corrado is quite good. Many believe that changing the exhaust will reap hidden horsepower and most assume the factory exhaust systems are restrictive. There is also something masculine about a healthy exhaust note. Aside from the subjective benefits of the exhaust pipes, there are other considerations.The object of the exhaust system is to evacuate the spent gases as quickly and efficiently as possible. The faster the exhaust gases exit the combustion chamber, the more horsepower the engine can produce. An efficient exhaust system will also increase gas mileage and engine efficiency. Contrary to popular belief, the factory exhaust systems on the corrado were designed very well. I it was made from stainless steel just like the most expensive aftermarket systems. It resisted rust very well and was quite heavy.
I had prior experience with some of the more popular systems that the aftermarket offered for VWs. All of them are well known and respected aftermarket tuners. System #1 was very poorly made which posed a challenge for fitment. VW exhausts are designed to be suspended by rubber rings. Hooks welded into the pipes correspond with hooks underneath the carriage floor. The hooks on system #1 were more than four inches from the carriage floor hooks! A phrase I've used in many posts--"where's the quality control? This system also did not fit tightly. VW did not weld their pipes but are slip fit. If the pipe ends are not tight, they leak which causes turbulence and thus inefficiency. System #1 had leaks galore and I was constantly trying to tighten the joints. After a year, I tore it out and purchased another system from another SoCal Tuner. This system, #2, in contrast was made very well. It fit and functioned properly. However, it's tone had a resonant frequency which was near the human voice making it difficult to speak inside the car! It also did not clear the rear trailing arm on my lowered suspension therefore would bump into the rear suspension when the car was loaded or hit bumps. I lived wit this one for a few years before giving it to a friend.
Critical considerations for me in California also included the fact that this is an emissions regulated state. Limited modifications were permited and had to be acceptable to the California Air Resources Board. In addition, clearance issues on a car with a modified suspension since the VW exhaust routes over the top of the rear trailing arm. That is a tall order.
I finally considered the Techtonics system. Techtonics has a well deserved reputation for quality performance parts, including exhausts. They are one of the few that actually test their pipes on a dynomometer to verify performance increases. The pipes are mandrel bent meaning that the inside diameter is uniform throughout the entire length of the pipes ensuring smooth flowing gases all the way out the back. I also opted to replace the Catalytic converter with a new one. Again I sought out the Techtonics which uses an oversized catalytic converter designed for a 5.0l engine! Surely it was adequate enough for my small supercharged 1.8l motor. The Techtonics system was far better than the previous two systems I tried and was even better than the expensive European Scorpion system my brother used on his car. 
The catalytic converter was roughly 10lbs lighter than the stock catalytic converter. In addition, the pipes, resonator, and muffler reduced the overall weight another 22lbs compared to the stock system! This was accomplished by eliminating the heavy "suitcase" resonator located underneath the rear seat. (See above illustration)
The stock system was still in good condition so I just removed it by loosening the clamps and sliding the different lengths of pipe apart. The catalytic converter required unbolting the unit from the downpipe. It also required I remove the O2 sensor.
I chose the aluminized exhaust rather than the more expensive stainless steel version. Here in California, we rarely see salt treatments due to snow, rain, or any other inclement weather which are hard on metals. The aluminized version is less expensive and weighs less than the steel counterpart. I chose the Borla muffler which has no seams and is polished. Too bad this isnt more visible from the outside.
The system overall fit better than the factory system and the techtonics system clearly has more clearance over the rear trailing arm! All of the hooks were in exactly the right place which puts very little stress on the rubber suspension donuts used to suspend the exhaust. The guys at Techtonics really tested their stuff in real life conditions. The result is a smoother acceleration, deeper exhaust note, and a more responsive pedal. Although I do sometimes activate car alarms in parking garages, the tone is not too intrusive in the passenger cabin. It was a purchase that is well worth every penny and its smog legal here in California.
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