While wasting time on the internet I read an article about dry sump oil systems. I have always thought this was used exclusively for eliminating oil starvation and enabling the engine to be mounted closer to the ground.
It turns out it also acts like a vacuum pump for the sump and lowers windage losses by not having the crank slosh trough the oil in the sump. The vacuum creates a bigger pressure differential from over/under the piston lowering pumping losses. Due to lower pressure in the sump piston rings can have less tension and reduce friction which can be as much as 20% of total engine friction according to this MIT study http://dspace.mit.edu/handle/1721.1/27129
This thread on a custom dry sump installation on a Honda pretty much sums up why this never has appealed to me: http://www.k20a.org/forum/showthread.php?t=98710
Lots of custom parts, fabrication, cutting, AN lines everywhere, custom pulleys and toothed belt. -------->vvvvv
But the MZR/Duratec engine has been designed to have a separate oil pump driven by a chain in the sump. This makes it possible to produce a dry sump system that have all components inside the sump like both Cosworth and Raceline have done:
Cosworth dry sump for MZR/Duratec:
This utilizes the stock oil pump but have an integrated scavenge pump in the pan driven by the same chain. Sprocket for the scavenge pump is smaller probably to make it spin faster than the oil pump to create the vacuum.
Raceline is even more compact but uses only one pump for both oiling and scavenging: