i put a new exhaust on my convertible 9-3 the other day and i took it for a ride i stepped on the gas and herd a loud bang in the front left of the car now the turbo seams to cut out about half way and there is no whistle sound after the turbo gage hits about half way. before i put the new exhaust on it was running really strong turbo would kick in and pull you back in the seat

please help