One of the little projects I'm working on right now is sketching something up for an upper intake. I've been in the 'toss spaghetti at the wall and see what sticks' stage, and there's a couple things I have questions on;
For starters, is there much more science behind selecting a throttle body other than not making it excessively large and making sure it's not the smallest diameter restriction on the intake system? In my case, the smallest diameter is the 2" outlet from the turbo and I'll have 2.5" in the intercooler, so it stands to reason I'd be looking around the 60-65 mm range for a throttle body. But I could be off base.
Secondly is more along the lines of intake design theory - My initial idea came from a turbo intake I saw on a 2JZ that wasn't much more than a welded up tube with plates on the ends and runners to the intake flange (first photo below). I started sketching something up that was a similar idea, but instead of having tube runners down, I just have it going straight onto the lower intake. This is based on using a 62mm throttle body, though as I sit here I would probably want 65mm since 62 is smaller than the intercooler piping... but I digress
I was trying to think of something that would be easy to fabricate out of simply produced parts, so the manifold flange and TB mount/end cap are just laser cut and welded up to the 4.5" diameter tube.
But back to the more theory question, does TB placement relative to the runners have much of an impact in a turbo build? I.E, is having the air coming in one end of a 28" long manifold going to cause issues with air distribution to the rear cylinders compared to the front? Would there be more benefit to having the throttle body more centrally located on the intake tube?