Popping the hood on the 2014 F80 M3 reveals a cramped engine bay sporting a 450+ horsepower turbocharged inline-6 cylinder
Here is a peak into the engine bay of the upcoming 2014 F80 M3. And yes, that engine bay definitely looks to be tight so working on it is not going to be a ton of fun. With the cramped bay and turbo (or multiple turbos) heat management will be an issue. That is why you see an aluminum water to air intercooler sitting on top of the motor. As far as power, with the new M5 sporting around 520-530 wheel horsepower stock
, the new M3 should be within 100 wheel of that based on precedent.
The E39 M5 put out about 340 wheel horsepower stock. The E46 M3 did about 275 so the E46 M3 had about 80% the horsepower of the E39 M5. The E92 M3 puts out about 350 wheel stock compared to the roughly 420 wheel horsepower of the E60 M5 which means it had 83% of the E60 M5's horsepower. If this is to follow with the new model, which it likely will to maintain the hierarchy, we can expect the new M3 to put out in the ~430 wheel horsepower range on a dynojet.
Time will tell and as soon as more specs are revealed BimmerBoost will bring them to you.