I have a 02 WS6 with an off road Y-pipe, by taking the cats off would I gain more up top then I loose down low? also would the car have to be tuned to get the most out of the off road Y-pipe?

 

Most any car will benefit from a tune. If your car was tuned already without it on, the slight increase in airflow (less restriction) might lean you out a hair. But it shouldn't be that drastic of a change IMO. As for what you gain and lose....I had an ORYP on my stock manifolds and I don't think I lost much at all. It may have moved my torque curve up in the RPMs slightly. But, I still managed to put down 329hp and 346ft/lbs with my untuned '99 SS on a local dynojet. That car had a lid, filter, g-maf, bellow, ORYP, and a Borla. Kinda wish I still had that car.