https://www.m3post.com/forums/showthread.php?t=1635216
Self-plug but you could consider a cutout setup if noise is a concern. I get straight pipe when I want it and quiet when I don't. Perfect for driving the gf around, or if I have guests.
Test pipes are good for 20whp, tune is good for 10-12 at the wheels, intake is good for another 10, and pulleys are good for 8. That's full bolt on. It'll bring most M3s to about 390 as there are diminishing returns to stacking everything. Full carbon plenum, long tube headers, and cams will bring you to 410. Those are all about $2000 each.
Rogue TPs and Alex@Alpine for a tune
Stock dynos at about 350 if the compression is healthy and on the newest software.