The lower numerically the gear ratio is the faster the cutting speed IF the engne speeds are the same.
I think if Jiffy would go to 20:1 or numericaly higher they would have a lot less issues with clutches, bogging, etc.
One of the sweetest augers out there seems to be the Husqvarna (see post with vid) and it has a 59:1 gear ratio. I believe the Tanaka is 40:1. Both use engines with nearly half the displacement and rated HP yet cut extremely well. My guess by looking at pictures is that they use some sort of planetary gearing to get these ratios without the bulk of the traditional gear case.
Now some of the old Eskimos Strikemasters etc with the Tecumseh and high numerical (40:1) ratios were painfully slow to watch cut.
Example: Jiffy runs about 8,000 RPM governed speed. My guess (being optimistis) is that they cut at around 5,000 RPM when not bogging. 5,000/15 is 333RPM
Husqvarna runs 11,000 RPM max and is rated at 8400 peak power speed 8400/59 is 142 RPM
Not sure what RPM the Tanaka runs?
The Husqvarna seems to just sing away and probably exceeds 8400 RPM during the cut. My Jiffy 2HP Pro turns pretty decent initially, but as the load increases the RPM's drop and it "flattens out" to a much lower RPM. I've seen the 2HP 12:1 unit cut and it's worse yet.
