Sorry Travis and all. It has been 10 months since Travis asked the tough question. I do not have reference links, as we were playing with this as a fun-thing-to-conquer. I lost my father and my Thailand business partner last spring, so my return to the States kicked things sideways.
Let me answer this way: My late business associate was part owner of API Tech in Thailand/Philipines. He was formerly the FI guru for HRC, and well connected in the Honda car world as well. He designed my CRF250L ECU/PCM. Sea level to 15,000’ with aggressive tuning. Fun and phone adjustments, if needed. Covid-19 has greatly impeded development.
What we were looking at with 2T’s was based on some historical features with a modern twist or three. Pipe “tuning” for some Bonneville blasters was done by adjusting the actual pipe length…exotic fuels, huge carbs, scary compression. By adjusting the pipe length as the pressure wave grew, they could sometimes complete a run without blowing the engine. Flatten the wave, giving the seals a chance.
A colleague here suggested that I play with exhaust outlet venturi inserts (in the stinger outlet @ the belly.) This was fun to do and quite easy, really. The only issue is that it works best for a WOT application, like a scooter. At or near wide open all of the time. Easy to change or fine tune. Not so good for a varied throttle or shifting bike.
We came up with idea options to build a tiny rotating valve in an oversized stinger port and use the EFI controller to tune it. Secondly we toyed with an two piece aperture valve, with a fixed tapered cone and a movable one. Inside/out arrangement.
We did test the venturi insert idea, (Sort of) using a simple throttle control from an E-bike. Cheap and easy. (Zero to 5 volt DC) The “sort of” part was using a rotating drum made from an aluminum rod. It was 22mm rod with a power valve like taper, ground to an 18 mm ID max flow orifice. It was inserted into the oversized stinger port with a piece of nylon as an external bushing. The 18mm is a good number for a 50CC 2T.
Sorry, but never got to testing it live on my Honda Gyro engine…but it worked well statically.