Is the only reason for test pipes is to use the oxygen sensors? At first I thought they served the perpose of fooling cops think that you have a cat but I am pretty sure that they will know. Are there any cops that will really get fooled by a test pipe, or a high flow cat like ebay calls them?

 

A test pipe is just a chunk of pipe that bolts up in place of the cat. I doubt anyone would think it is a cat.

 

Test pipes are used for flow......some just look nicer than others.

 

I bought my car with a test pipe already. I guess it's time for a hollowed cat living in california and all.

 

Of course you realize a hollowed out cat will fail smog as quickly as will a test pipe...yes?

 

it's a violation of federal law to disable/remove the cat on a car that was originally equipped with one. you can be fined $25,000 by the EPA. test pipes are used to replace the cat so that everything bolts up right and to give your o2 sensor a place to go.
i would rather have a 3in high flow cat than a test pipe. test pipes stink and carry huge fines.

 

...it's also a violation to rip the tag off your own matress...

If I lived where there was routine smog inspections...I'd always run a stock cat, get a high flow cat(carsound prolly), ...or move to a more sensible state.