I don't know where you live but in the US it is illegal to remove the catalytic convertor unless there was something wrong with the prior one. In California, the only way you will get an honest repair shop to put in a free flow catalytic convertor is if the one on malfunctions. Aside form the fact you can be fined heavily, the volvo, like others have noted, will put out errors in the codes because of the change. If you want to get more horsepower, there are other things to do, such as the free flowing exhaust and the chip mods. I highly recommend leaving the convertor alone. It's there for a reason.

Delgado
San Diego, CA