It's no secret that naturally aspirated engines tend not to tune as well as cars with forced induction (in most cases). The E46 M3 is typically one of these cars with low performance gains on a standard car. Yes you can improve drivability, but to get a decent power increase, you need to install a CSL (or CSL style) airbox, which is exactly what the owner of this car did.
You may remember this car from when we dyno tested it initially completely standard and it produced really good figures, but that was on our old dyno.Since we last tested the car we have replaced our dyno so went ahead with another standard test before we began tuning the car.
The owner was hoping for a conservative 340 bhp which is still a brilliant gain over standard. With the CSL airbox installed, we were able to surpass that, by quite a lot! The graph below shows the difference. We raised the rpm limiter because the car was producing power all the way to redline. In cases like this it's beneficial to raise the rpm limit to allow the car to make more power.
Power gained: 26 bhp
Torque gained: 28 nm @ 7,500 rpm