Quote Originally Posted by Fastjeff57 View Post
The problem with running poppet valve exhaust valves in a two stroke is that they are severely rpm restricted. Where as a 4 stroke opens the valves every other stroke, a 2 stroke would have to open them every stroke--think 14,000 rpm like operation in a 7,000 rpm motor. True, present Formula One motors run 18,000 rpms (and could rev higher if allow by the FIA), but they're not reliable enough for operation for more than a few hours (using nitrogen gas springs).

The Aussie Orbital 2 stroke used such a system, and quite successfully. Ford and other Detroit auto makers seriously considered installing one of them in compact cars. (I recall seeing a Ford Escort with one that had great performance.) With direct injection AFTER the intake closed, they were clean enough to pass 80s emission standards, but looking stricter standards are what probably killed the idea. Mercury ran a few test power heads using Orbital power--I recall a video of one--but they dropped it as well. Perhaps the time to resurrect the idea has arrived?

Jeff
You're quite right about RPM limitations. But you might be surprised: The 1990 Cosworth cylinder head used for HKS was rated to 13,800 RPM with conventional springs. Dividing by 2 gets you 6900 RPM - quite useable given the correct prop. My plan was to swing an 8-1/2" X 17" with the 1:1 45SS gearcase. The math worked. Sadly, the engine didn't deliver. Too heavy, too complex, too expensive, but a cool project!!! Perhaps this winter the VHS video might be digitized for YouTube.

Regarding the Orbital process, it seems to me the Mercury Opti-max is the air assited Orbital system in two stroke application. Can anybody comment?

Tim