Pretty old thread! You can replace the cats with test pipes, but you WILL throw a SES light unless the test pipes have non-fouler connections. It will also be louder and prone to rasp. As long as your purchase test pipes specifically made to fit, then they should bolt right up to your Stillen system.

Good Luck!

 

 

Some test pipes have a small tube welded onto the main pipe to relocate the O2 sensor further from the exhaust stream, ones that don't typically require "non-foulers" which thread onto the pipes and have a small hole for exhaust gasses to pass through. The G usually requires 2 sets of non-foulers, drill out the first set so the hole doesn't reduce (basically makes the non-fouler just an extension bushing" then screw on ANOTHER non-fouler and leave it alone.

The whole point is to move the O2 sensor further from the fast-moving exhaust stream and reduce the flow across the sensor. test pipes like the Motordyne ART pipes and Fast Intentions test pipes don't usually require non-foulers because of the extension tube they weld on.

 

^what he said, but they do make extra long non-foulers that you only need one set of. SES is what our cars have instead of a CEL, it means "Service Engine Soon".