Designing an engine from the ground up is a very very very difficult task. Designing aero parts is relatively less difficult because the manufacturing is a commonly-known process that most of the engineers would know. Not to say that designing aero is easy, but it’s usually a single guy’s vision pulling the rest of the aero staff in his direction.
Designing something that can make 800 horsepower without exploding/disintegrating and going through 2-3 races while having atleast 50-100 moving parts is not something that can be developed over a period of a year.
There is a reason why Ferrari or Mercedes engines make the amount of power that they do while having the reliability. They’ve been at it for dogs years and their current designs are always a refinement of the designs used in the making of the previous engines which includes decades of experience. There is hardly a revolution in engine-building unless you throw a completely new set of rules at the engine manufacturers. Consider how long Mercedes engines have been the most powerful and you’ll understand what I’m saying.
Secondly, building a bulletproof engine requires more engineers from more faculties than the rest of the car’s staff put together. You need metallurgical engineers, electrical engineers, chemical engineers and who knows how many more.
Sorry for the wall of text, but I build engines and cannot stand people who think that a new engine can be developed over a weekend while sitting on your couch in the living room.
This is not to say that they won’t ever get to it. McLaren have already got their hands into the bucket by building the 12C engine, but compared to the engineering required to build an F1 engine, the 12C’s engine is nothing. They’ll get to it for sure, but don’t expect them to be reliable or powerful if they’re running a McLaren engine inside during the first race in 2013.