[HiPSI]

here's another way to look at it... turbos spin because exhaust gases go through the fins of the turbine wheel. they move that direction because anything that's in a pressurized system will always try to take the path of least resistance. 2" exhaust = a good bit more resistance than 3" exhaust, and decreased resistance on the exhaust side of the turbo means you would gain in spool time (thus beginning to make power earlier increasing your overall power curve). you'd also see some gains on the top end when your car really needs to get rid of the exhaust gases as quickly as possible.