I got a flowmaster dual outlet exhaust system. The stock system comes with a single outlet 3 and a half inch piping all round. However when I got mine installed (the flowmaster Dual) I got the two 3 1/2's going from the headers to a y pipe 2 1/2 inch and through the flowmaster muffler and out to 2 2 1/2 inch outlets. Is this size difference going to slow me down. Please advise me.

I got a flowmaster dual outlet exhaust system. The stock system comes with a single outlet 3 and a half inch piping all round. However when I got mine installed (the flowmaster Dual) I got the two 3 1/2's going from the headers to a y pipe 2 1/2 inch and through the flowmaster muffler and out to 2 2 1/2 inch outlets. Is this size difference going to slow me down. Please advise me.

I doubt it, or not anything you'd feel anyway. In general you don't need full diameter all the way to the outlet since the exhaust gasses have cooled and contracted some by then.

Full diameter to the outlet makes a better sound though, which may trick you into thinking you've got more power.