Do a 2.25 inch exhaust, that engine is not making nearly enough power to warrant 2.5. As a general rule, more free flowing exhausts = more horsepower/top end and a more restrictive exhaust = more low end torque. Example, 2.5 in will support 400 horsepower. If you installed a 3 in, you'd get more top end and if you installed a 2.25 you'd get more low end. Obviously there is a lot more too it and it is possible to be too restrictive and too free flowing.