was going through the literature at http://www.echo-usa.com and found some info.
the srm-2200 is the same 21.2cc as the current srm-2100 but the parts look more like the 25.4cc engines. also the srm-2100 is rated at 11,000 rpm while the 2200 is rated at 8,000 rpm, so maybe it has a longer stroke than the 2100's 26mm and was designed for more grunt at lower speed. might be good for big props.

dave