The step in size on mine is factory, all I have done was install a new better flowing muffler, mines a 78 though and is a factory super six car.

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"if it aint broke, fix it till it is"
78 Plymouth Volare Super Six wagon
89 Volkswagen Golf GTI 16v
92 Chevrolet K1500 5.7
98 Ford Escort ZX2 zetech

If you are looking for a quiet but also free flowing muffler with a 2 1/4 inch inlet and 2 inch outlet, try this one:

http://www.summitracing.com/parts/WLK-21110/

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Casually looking for a Clifford hyperpak intake for cheap.

Thank everybody for your help.

I decided to give it a try, but the increase is very conservative. The front pipe will be 2" and the rear 1 3/4" both 1/4" bigger than factory (according to exhaust manufacturer). This was the size the manufacturer felt confortable with and I guess the risk of running into problems should be smaller too.