I will give the torq converter a try.
Since it will let me get high speed and at the same time have lots of torque when needed for speeds, I think it is a good idea, however they are expensive.
I will use the torque converter on another bike I plan on building.
Does anyone know where to get 10g (3mm aprox) spokes? , the largest I have seen available are 12g.
12g is perfect for the 70cc, which is 3.5HP, but for a bigger engine the 10g spokes might be needed.
I will use the torque converter on a 4 stroke engine with a 3/4" shaft, there is a chinese engine at harbor freight that will be on special for $130 (june 1) 6.5HP that I think will be great for that since it is cheap and has a lot of power.
That engine runs at 3600 RPM (governor), so it will need a very large rear sproket about 56 tooth and will give you 50 MPH flat, and on worst hills probably 17 MPH due to the torque converter reductions.
Does anyone know a source for a very large bicycle sprockets?
One possibility is to use a jackshaft, but I rather keep things simple if possible.
Does anyone know where to get a heavy duty engine mount for a 4 stroke engine?, like the ones that appear on the 4 stroke kits for the 50cc engines.