Thanks!

 I would do 62mm for a single throttle body on a 3.1 with 7000rpm peak power (stock is 54mm I believe). Dividing that by 6 asks for 25mm individual throttles but thats not how ITB sizing works apparently:

"When sizing ITBs, you need to consider that each individual throttle needs to be large enough to not overly restrict air flow into its cylinder at high RPMs.  This required size is usually close to that of the intake port.  If you add the total cross-section area of each TB in an ITB setup, it will add up to an area noticeably larger that the TB size required for a single TB setup.  It is this characteristic that makes ITBs act like grossly oversized throttles at low RPMs.  This is why you want to also be careful to not select a TB size larger than you need because this will work against you at lower RPMs.  The smaller the TB, the better modulation you get at low RPMs and the higher the intake air velocity will be.  Higher intake air velocity helps air/fuel mixing and can noticeably effect performance.  EFI does not rely on the venturi effects that carbs do, but intake air velocity still effects performance.  The selection of an ITB size is then a compromise between these multiple design choices."

http://77e21.info/mstuning_tbsizing.htm

Everything I have seen for the M20 is in the 40mm range and I have read that the Dbilas setup is oversized (42 or 45mm, I cant remember)

Then there is also this from a throttle body manufacturer

http://www.jenvey.co.uk/jenvey/throttle-body-selection-with-jenvey-dynamics

Factors influencing size are; Power output, RPM, cylinder head design, cylinder capacity, position of the throttle body in the inlet tract and position of the injector.

Choice of bore size is a balanced compromise resulting from the following; 

1. A larger bore leads to lower flow resistance, but obeying the laws of diminishing returns. 
2. A smaller bore leads to better throttle control and response (never underestimate) and improved fuel mixing. 
3. The system should be considered in total - from (at least) trumpet flange to cylinder and proportioned accordingly.

Basic references for BHP per cylinder, assuming ca 120mm from butterfly to valve head and a max of 9,000 rpm are; 
Up to 30 BHP - 30mm, up to 33 - 32mm, up to 39 - 35mm, up to 46 - 38mm, up to 51 - 40mm, up to 56 - 42mm 
Up to 65 - 45mm, up to 74 - 48mm, up to 80 - 50mm, up to 87 - 52mm, up to 93 - 54mm. 
These power figures may be increased by up to 10% in a purpose designed and well proportioned system. 
As butterfly to valve distance increases, butterfly size will need to increase in proportion to system taper and vice versa. 
Lower revving engines and those with injectors placed before the butterfly will generally accept a larger body.

I also machined a crank spacer today.

http://www.ausrotary.com/viewtopic.php?f=4&t=205130

check out this guys whole website dedicated to the topic/design of your camera 'aperature' style throttle:

http://www34.homepage.villanova.edu/stephen.m.miller/IRIS%20Throttle/preliminary_ideas.htm

basically, yes, the aperature style is more efficient, but its stupidly complex and really large in size, which would make it very difficult to use in an ITB setup, but not terrible with a single throttle.

to me, cylindrical (used on F1 cars) or slide throttles seem like the best alternatives to the classic butterfly. both allow 100% unobstructed airflow at WOT, and are still simple enough (but still not as simple/cost effective as a butterfly)

REKIII said:

Neat concept, but the pecision on the plates would be cost prohibitive, also getting that rotation with equal force would be

Should be able to cnc machine them no? I could use the machines at school for free. I was thinking of adding a tongue and groove along the edges of the shutters and like a teflon gasket between the moving shutters and those two center rings. With a little oil should be able to move and seal quite easily, in my mind lol.

why would you even try to start it without a manifold lol how is doing that? I suppose it could still idle if the air flow meter was still plugged in

Valvetronic is wild

Super neat concept.

Maybe look at a lest complex design where 1 or 2 plates slide in from the side(s).  This would be easier to seal.

Here is v2, trying to make it more compact:

http://www.youtube.com/watch?v=xjSNiTF_u-k&feature=youtu.be

Just realized I posted this in the BMW discussion instead of technical... move it if you desire

How about a rubber sleeve (think of something a little thicker than a balloon)  that is full throttle when untwisted, and closed throttle when twisted.