There are a few cheap and easy ways (along with some very expensive ones — I can discuss other stuff on this car if this sort of stuff interests you) to get more HP out of a M5. There are charcoal filters in the air induction that restrict airflow. Good for ~5HP if you’re not so picky about what goes into your engine. I guess. You can put in a RPI or Dinan pulley; cheap and easy. You can also put in RPI scoops. Cheapest extra 10-15HP on earth.
By default air comes in, around the radiator, and into the air intake where some is vented back out to cool the front rotors and the rest is sent to the engine. Problems being no forced air induction, and the air going into the engine hot which means the engine has to lean the mixture and you lose HP. Cool, forced air - much bettah.
This is the front before:
Here is what it looks like with the scoops added:
They look a little mismatched but it’s because of where the scoop needs to reach is different on each side and so it goes. The design has since changed to make it symmetrical (the maker is active online and very responsive — good guy). With the kidney grills back in and hood closed they’re hardly noticeable but it does give a good “what the fu..” to anyone who does happen to notice out of place red parts.
The reason that I think it works is because the ECU seems to have readjusted a number of settings from the previous 4,000 miles without it. However all of those miles were highway and those since the scoops haven’t been proper highway — choppy traffic, not 85 mph. So who knows. My butt dyno isn’t that sensitive.
I watched a youtube video earlier of a guy drilling holes in his muffler to make his car go faster, on a budget. It made me think I should offset the defecit that guy left on the internet by pointing out there are better ways.