Aloha,
Lapperl- If you are thinking of doing this on a vehicle you must also;
1. Change the timing in a major way, about 90-120 degrees after TDC.
2. Change the cam gear to run 1-1 instead of 2-1.
3. If the ignition is not run off the cam, you must make the ignition fire twice it's current number of times.
4. Remove about half the trailing edge of the intake cam lob.
As you will be converting from a 4 stroke to 2 stroke.
h2opower- It is my understanding that Stan ran the exhaust back into the intake to slow burning, as a result of the exhaust contained no flammable gases.
The piston is also pushed by adding fresh, cool nitrogen from the atmosphere, as the nitrogen (85% in air) expanded greatly in the combustion process.
As your engine will be breathing much less air, and hydrogen as the fuel, you will need much less intake of fresh air, yes, this will use and run on much less hydrogen than a conventional gas engine.
Bill