[dcaron9999]

In your early 135i, you have the N54 engine, secondary cats on you Mid-Pipe. I have the N55 engine in 2011 135i, which has no secondary cats and a single resonator /y-pipe.

I just installed a catless downpipe on a stock exhaust two weeks ago, and loaded a custom PTF/Cobb tune. The noise at cold start (lasts 40 secs) is embarrassingly loud. I did a YouTube video and will post a link here.

After the cold start, it sounds pretty good. Only noticeable when you step on it. No drone in the car. I was about to install Vibrant Performance resonators to muffle the sound and make it more deep sounding, but decided to wait...

Moral of the story. If you plan in installing a Downpipe, don't get an exhaust or modify anything else until you hear the DP on its own.

Welcome to the forum. Im from Mirabel, if you ever want to meet up, or come to a track event ...