I have a STOCK 2013 Honda accord exl 4 banger 2.4l, I want to keep it stock very reliable was not meant for a turbo/electric turbo/supercharger. This is my only car. But I wanted to modify 1 thing.
I wanted to modify my exhaust but I didn’t like how other 2.4 sounded with the custom exhaust… it sounds like a brass instrument, and all the other options for a nice sounding exhaust are like $300+. So I was drunk one day with my buddy’s and they’re making fun of how slow I am. So I get the drill and do 8 nice ones in the bottom of the muffler. It’s been about 6 months and 15k miles later all good. And it sounds amazing. Here’s a YouTube link

https://youtube.com/shorts/2-gHfD2e5s0?si=ZQixmFQjj9dMnxac

it’s not tuned nothing. I’m just wondering if this is making me run lean? or does the car need more back pressure from the exhaust ? Does it make me slower? No clue oh yea and 145k miles on it. No light’s perfect condition. Will drilling holes in my exhaust make my car crap out earlier than it’s supposed to? Etc. thanks!

 

I suspect you'll only see a difference in sound with drilling holes in the muffler. Look for any wire harness where the exhaust exiting the holes in the muffler could cause damage to be thorough. I'm guessing the holes are drilled on the bottom of the muffler and shouldn't cause an issue.

The modification is far enough downstream that it shouldn't affect the O2 sensor in the catalytic converter for air/fuel ratio. If you want to be 100% sure, get an obd2 scanner and monitor the short and long term fuel trims at idle and 2000 rpm. 0% fuel trim is "perfect", where anything within +/- 10% is normal. If the fuel trims stay pegged at 20-25%, then you'll have to investigate. You can get an inexpensive bluetooth obd2 plug on amazon and the torque pro app (<$10 for the app the last time I checked) that can help you monitor. My TSX has a similar engine as your car and the short term + long term fuel trim sum is +/- 7%.

 

With exhaust exiting the muffler under the car you could literally kill yourself from carbon monoxide poisoning due to exhaust in the passenger compartment of your car. Long story short, drilling the muffler was a very bad idea.