Well known that a 4 valve per cylinder head has rpm to rpm variances in air flow due to non homogenous nature of fuels, air, and shock waves.

http://in3.dem.ist.utl.pt/down...4.pdf

Pretty impossible to make each intake valve flow the same amount at differing rpms.

Makes using a flow bench to optimize heads 10 times harder [more expensive] than a single intake valve engine.

Also comples is the cycle to cycle variation of the injector spray pattern:http://www.delphi.com/pdf/tech...2.pdf

very interesting.

do you think as DI makes its way into more gasoline engines, injector spray pattern differences will make less of a difference?

If the US can ever get its gasoline quality up to the standards required for direct injection. Pretty difficult when we buy the worst crude available from Mexico and Venezulea because Citgo refineries were designed to work with this garbage.........ultra high Sulfur........tarish crude.

Until something is done to replace the current EGR and filters/catch cans are added to PCV systems we will always see gunk in intake track........which will distrupt air flow.

yeah these sulfer problems are only going to get worse and worse. there is a exxon-mobil refinery up here in joliet, il, that is the only one in the country that can process this super-sulfer enriched crude from some part of canada at a profit...and with the kind of fuel ive been getting around here(not kind to the injectors) i am skeptical as to how well this plant is actually running.

i wouldnt think it would be all that hard to implement a catch can, and servicing wouldnt be much of a concern...

but it seems motives in the industry arent always where one would hope.