500hp on stock B58 turbos with E85 is possible but youre at the absolute limit. Most people see 470-490hp. 500+ usually needs upgraded turbos.
500hp on stock turbos is achievable on the B58 but youre right at the limit. You need catless downpipe, FMIC, intake, and a very aggressive map on E30+ ethanol blend. On 98 octane, 460-470hp is more realistic for stock turbos. Going beyond 500hp reliably requires upgraded turbos. The stock B58 turbos start running out of efficiency above 22-23 psi.
I made 495hp on my M340i with stock turbos on E40 blend. Mods: VRSF catless DP, VRSF 7.5 FMIC, BM3 stage 2 map, upgraded charge pipe, and a port injection kit for the ethanol. The car is incredibly fast but I can feel the turbos are maxed out - boost tapers off hard above 6000rpm. Next step is Pure Stage 2 turbos for 600hp+.
