the welding on my resonator pipe in the exhaust broke, and air pressure leaks out, air still reaches the muffler but it leaks allot before reaching it cause when i used seafoam the smoke leaked from undernieth the car and the muffler, and its easy to see, anyway will this cause any form of lost in performance?

 

You will see a noticible loss in power b/c there is air coming into the pipes making some exhaust back up and not all flowing smoothly out the end. Depending on the size will determine how much loss

 

I noticed a drastic decrease in performance when my exhaust broke just before the resonator. All fixed now ($450 later) and it feels like a new car.