DC piping question

[socrates]

Ok, I know the general concencus is to use 2 45deg bends together to make a 90 so that the transition is more smooth and open, but I would like to quiz you guys on the following...

I'm not to sure what kind of storm water pipes you guys have over there, but here in Australia, the 100mm (4") pipe bends have a smooth transition along the inner and outer radius for the 90deg but the 45deg only has a smooth radius on the outside, the inside is not a radius, but rather the 2 45deg planes meeting at a point.

So, with this in mind, would it still be better for airflow to use the 2 45deg units to make a 90deg turn, or just use the single 90deg piece yeilding a tighter radius but a smoother path?

[socrates]

PS excuse my dodgy paint drawings, I've recently formatted and am yet to install my graphics software!

[socrates]

Or we could just forget about the entire question! I just a bit of a play around in the shed and figured out that due to space constraints in certain areas of my intended piping layout, I will have to use 90's as to not cut holes in anything! One of these days I might get around to testing the theory of how the 2 elbows perform, maybe.