I figure he should be at least 400whp....since a couple different stock M3's have tested in the 370's....
Another factor is when BMW designs the ECU's they do it for the worst possible combo of poor fuel and extreme weather....so the engine won't grenade under high load in hot weather with crappy gas.... Yes the ECU can compensate for enviromental and fuel conditions, but it only senses "bad" gas once a knock or ping is registered....... So there should be a subsantial safety margin in the stock ECU...
SO a tuner that is tuning the engine for higher octane gas...say 100 should be able to get some good gains....add an exhaust and intake and the gains keep going up....since the race M3 is rated at 485hp (I'm sure thats way low) that should be attainable with race gas and exhaust work.....
2008 E92 M3, MR, DCT, extended BB leather, loaded!
1988 Porsche 928S4, Guards red/Champagne leather
1989 Porsche 928S4 track beast!!!