My 850 has a Magnaflow catback exhaust. On another forum I was reading that these engines require backpressure due to the way they're designed, and thus backpressure helps horsepower gain. He says a catback adds 10-12 hp and 5-6 ft lbs torque versus a straightpipe which gains 1-2 hp and loses torque. Is this correct? Because I'll be made if the exhaust I spent money on isn't the best for my car. Thanks for any replies.

 

You should be fine.

If you are NA then you want some back pressure. Turbos like free-flowing exhasuts.