Throttle methods

Have been thinking about various throttle mechanisms, the options are:

• Butterfly valve
• Roller barrel
• Twin roller barrel
• Sliding plate
• Twin roller profile
• Iris (I've not seen any constructed like this, and would have poor flow characteristics - variable orifice plate)
• Flaps (sort of a twin butterfly)
• Twist mesh (slightly off the wall, and would need fatigue resistant filaments, but would be like the iris but with a venturi profile)
  

The primary search criteria is to extend the part throttle opening characteristics, i.e. to reduce the rate of opening for better control. But this also means keeping the fuel well mixed with the reduced air flow, and stopping it from ending up on the side walls.

Have played with roller barrel throttle bodies and believe that the size requirements are constrictive. The advantage of the butterfly is that it directs the air flow towards the injector at low flow rates thus encouraging mixing.

The construction for the butterfly version should be achievable through suitable casting and milling operations. Will need to save up for a large milling machine, and stepper motors to convert it to CNC, looking on the web a pretty sizable mill can be had for ~£700. With stepper motors available from ~£100 for a set of 4, but this is a long way down the line, need to build up casting kit first.