I did this back when I was in the mid 90's. My car was running low 10's at the time. I cut a hole in my inner fender to dump the exh in my front wheel well. I didn't go as far as drilling a hole in my fender, but the concept is the same. It made my car sound as though it was on steroids. With back to back tests at the track, I netted zero gains when it was capped up and ran through the exhaust.
This was my fender dump
This was the exit hole in my inner fender..... As you can see, heat isn't friendly on plastic, thankfully my coolant bottle covered most of the exit wounds. The inner fender is now out of my car and another clean factory original has taken it's place. If you are interested, I can sell you my inner fender for you to dump your exhaust there as opposed to cutting a hole in your metal qtr panel.