Project E36 323is: Building the Poor Man’s M3, Part 4 – Exhaust



E36 323is dyno
Okay, so there's one thing that everyone reading this is starting to ask, which is, “What about power?”  While many people go with an aftermarket cat-back exhaust thinking that they're going to gain 20+ horsepower at the wheels, I'm here to tell you that's not going to happen.  If you're doing headers, removing cats and doing a straight-through system all the way back, maybe, but even that's a stretch. What you're really getting with an exhaust is weight reduction, looks and sound, with a side effect of a slight power gain.  We were curious, though, so on the dyno we went… 
E36 323is dyno chart
As we said, there simply isn't a lot of power to be gained with a cat-back exhaust alone, but there are gains nonetheless.  Based on the dyno graph, you can see that we had pretty much the same gains across most of the rev range, so there's not huge peak gain, but it's a decent gain across the board.  Our baseline numbers maxed out at 141.1 whp and 142.9 wtq.  Post exhaust work we managed 146.8 whp and 149.5 wtq, so nothing out of this world, but considering it's our first and only power upgrade so far, it's not that bad at all.  It's definitely got us looking forward to seeing how much more our little M52 has to offer.



  1. This is really dope, but I have a question regarding the O2 sensors and wire harness.
    I know for the 323is exhaust there are only two O2 sensors. One before the cat and one after. but on the 328 exhaust theres a total of 4 because of the dual cat setup. Did you have to use the s52 wire harness for this setup? I did this exact same engine build on my 323is and im wondering if the s52 tune I have on my ecu will run properly with my standard 323is exhaust

    1. Curious to find out too about the o2 sensors. I am looking to do the same with m3/328 downpipe all the way to the muffler. Also wonder how much power gain in real world (0-60 time).

    2. I did this exhaust swap on my 323ic and now have an engine code P0133 after relocating the single pre cat sensor to one of the headers. I’m at my wits end and don’t know how to fix this issue without getting a whole new wiring harness for my car. Anyone else who’s got an idea of what to do please reply.

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