Originally Posted by Shmoo

Yes, they do. If you read the EO article from CARB on the Greddy kit for the GSR, it clearly shows that a new Greddy equipped GSR puts out less "smog" than a new GSR in every possible area of the test.

I don't know if it really has anything to do with heating the cat up better, but rather something the turbo does to the efficiency of fuel combustion to make it cleaner all the way around.