I think we're just talking about slightly different things. I believe you're talking about only changing the helix and seeing the effects.
I'm talking about a complete clutch weight and spring design using a specific helix. What I mean is once the system is tuned to provide the correct engagement rpm and peak hp rpm during wot accelerations you get the effects I described above.
The way the few clutch gurus whos brains I've picked approach clutch tuning is as follows (it also makes sense from an engineering perspective):
- think about the type of throttle response you require, the rpm shift between peak torque and peak hp, and select a helix (in a perfect world you want the upshift at light throttle to keep the engine at or slightly above the peak torque rpm). If maximum speed is important, keep in mind steeper is less efficient at top speeds and make a compromise selection (not as steep).
- figure out how much belt clamping is required for no belt slip (once the primary has fully engaged, but before shifting occurs) and select a secondary spring that works with the helix to provide this minimum at all times (the steeper the helix, the stronger the secondary spring required).
- select a primary spring and weights and keep tweaking the primary until the rpms are where you want them throughout the entire wot throttle range.
- if the throttle response isn't what you wanted (due to clutching) or the belt is stealing too much high speed hp select a different helix and start over.
If you take this approach the big descision in the system design is which helix to run. It drives the selection of everything else and the big tradoff is steeper angles keep the rpms more constant (once everything is optimized) and smaller angles place a more appropriate clamping load on the belt relative to engine torque. If you go with too high an angle and have a peppy machine but the top end will be down somewhat and the belt will wear faster at high speeds.
One of the many antiquated machines I have is a 1966 Olympic (I have a barn full of cars, snowmobiles, trucks, differentials, transmisions, engines, ring & pinions, posi units, etc., etc.). It doesn't have a helix at all (effectively running a 90° helix). That system is unaffected by engine torque, just track speed (once moving). The rpms for a given speed are constant, regardless of how much throttle is applied (well, extremely close). One advantage to this is all 9 hp is available instantly at any time because the engine always operates close to its peak hp.
Apparently the historic reason for the use of a helix was to get around the over clamping of the belt at high track speeds. Prior to the helix, belts were failing regularly on all of the higher performance machines (25 hp and up). The ability for the engine to run a lower rpm under lighter throttles for the same track speed and having a better top speed were secondary advantages. There have also been major improvements in belt designs over the years also.
I'm envious of your snow... They now even took away the falling snow picture for Thursday (indicating we're not getting any) at the weather web page for Ottawa:
Hope you have a good holiday and get lots of sledding in. Where abouts are you located?