i found the cat in my car to be hollow when i had the exhaust done, the shop just reinstalled it for me. is this a performance gain or loss? 1990 90 20vquattro.
thanks
dave

may free up some HP, but you are prolly loosing a bit of low end torque. a decrease in backpressure causes that to happen. on a turbo, its great (low BP). on a NA engine, especially a smaller one, its not so great. theres a fine balance of too much or too little BP. you'd have to get the car hooked up to a dynapack setup to tell anything. your butt wont notice either way. to take advantage of a high flow-capacity exhaust tract (valves, cam, header, cat, muffler), you have to have a high flow-capacity intake tract (filter, MAFS, TB, IM, valves, cam). you would also have to tune the fueling if the ECU didnt do it for you (injectors, rail, fuel pressure reg, and possibly pump on the 7A cars).