I am in a debate with another enthusiast about the theories of exhaust flow. The specific instance is a 95-97 dual cat Y pipe that has had the cats gutted and rewelded to resemble stock. He claims that there is an increase in performance and I contend that a performance increase is doubtful. My opinion is that simply gutting the cats can eliminate some backpressure, but due to the rough and varied dimensions, the flow would actually be disturbed by the turbulence created by the now gutted cats. The drivers side cat appears to be the worst culprit. If it were gutted, the exhaust would exit the manifold, down the headpipe, into the cat with a rapidly expanding internal dimension that then rapidly necks down again. The passenger side cat under the floor is a different design but still would creat the same effect. Just as every bend in the exhaust pipe causes the air to change direction and have different velocities at each axis of the pipe bend, the gutted cats would produce small eddies in the flow that would disturb flow at higher velocities. The correct solution for a stealth off road pipe would be to make a solid pipe running through the cats and the shell of the cat rewelded around the pipe. This would, form the outside look totally stock, yet a smooth and consistantly flowing pipe would produce the best flow at WOT.
Before someone says that dual cats started in 96, California cars used dual cats in 95 even though still OBD1.
Am I just exhausting hot air?
Before someone says that dual cats started in 96, California cars used dual cats in 95 even though still OBD1.
Am I just exhausting hot air?
The block was painted factory black, stock valve covers, stock headers, stock intake, larger turbo under a stock turbo shield, No gauge pods or 5" tachs on the dash... I mean it looked like Grandpa's car. Gramp's car that ran low 11s 
that is.
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