T
tollen77
Member
There's been a lot of talk recently regarding BRP's switch in the '09 Summits from the 42 helix to the 43/47 in the secondary yet very little about the switch to a 413 ramp to the 441 in the primary. I'm hoping this thread will get the discussion started.
I still have a lot to learn regarding clutching, though I've learned a lot in the last couple years. The one thing that I haven't found much info on is ramp angles.
As a refresher for those that don't know, the TRA primary has three arms that swing outwards as RPM increases and swing back inwards as RPM decreases. They swing on a path guided by three ramps. These ramps are attached to the moveable sheeve of the primary clutch. As the arms swing outward they slide along the ramps and in doing so close the primary. The more the primary closes, the greater the effective 'gear ratio' of the drive 'sprocket'.
As the belt is pinched by the primary clutch it forces itself further down in the secondary clutch. This also further increase the effective 'gear ratio' of the system. (Think of shifting up or down in gears on your 10 speed.) As the secondary turns it does not directly drive the track through the chaincase and axle. The helix distributes the amount of load provided by the secondary to the jackshaft faster or slower depending on its angle. The steeper the angle (44,45,46,47,etc...) the faster the helix transfers load the between the jackshaft and the secondary. The shallower the angle (42,41,40, etc...) the slower the load is transfered.
Back to ramps;
It is the curvature of the ramp that adjusts the timing and the degree to which the movable sheeve of the primary slides in and out at a given RPM.
Here's where I'm a little uncertain (If you have something to add or change to this description, please do):
I believe that the more aggressive the curvature of the ramp is, the faster the clutch will close and therefore, the faster the primary will shift. This, of course, depends on the load that will be placed on the primary (and therefore the engine) by the track through the secondary clutch.
- If the curvature of the ramp is too aggressive relative to the power of the engine, the engine will bog and your sled will accelerate slower.
- If the curvature of the ramp is not aggressive enough relative to the power of the engine, the sled will not accelerate as quickly as it could as the engine isn't working as hard as it possibly could.
This leads to what I beleive to be a clutching law : The more powerful your engine, the more aggressive the ramps in your clutch can be.
Correct????
One more question: There is clearly a difference in a 413 ramp compared to a 441 to a ______. With a helix the number that describes the helix refers to the angle (or angles) of the helix. I assume the numbers 441 refers to something as well. What is that something???
If anyone has anything has anything else to add, please do.
I still have a lot to learn regarding clutching, though I've learned a lot in the last couple years. The one thing that I haven't found much info on is ramp angles.
As a refresher for those that don't know, the TRA primary has three arms that swing outwards as RPM increases and swing back inwards as RPM decreases. They swing on a path guided by three ramps. These ramps are attached to the moveable sheeve of the primary clutch. As the arms swing outward they slide along the ramps and in doing so close the primary. The more the primary closes, the greater the effective 'gear ratio' of the drive 'sprocket'.
As the belt is pinched by the primary clutch it forces itself further down in the secondary clutch. This also further increase the effective 'gear ratio' of the system. (Think of shifting up or down in gears on your 10 speed.) As the secondary turns it does not directly drive the track through the chaincase and axle. The helix distributes the amount of load provided by the secondary to the jackshaft faster or slower depending on its angle. The steeper the angle (44,45,46,47,etc...) the faster the helix transfers load the between the jackshaft and the secondary. The shallower the angle (42,41,40, etc...) the slower the load is transfered.
Back to ramps;
It is the curvature of the ramp that adjusts the timing and the degree to which the movable sheeve of the primary slides in and out at a given RPM.
Here's where I'm a little uncertain (If you have something to add or change to this description, please do):
I believe that the more aggressive the curvature of the ramp is, the faster the clutch will close and therefore, the faster the primary will shift. This, of course, depends on the load that will be placed on the primary (and therefore the engine) by the track through the secondary clutch.
- If the curvature of the ramp is too aggressive relative to the power of the engine, the engine will bog and your sled will accelerate slower.
- If the curvature of the ramp is not aggressive enough relative to the power of the engine, the sled will not accelerate as quickly as it could as the engine isn't working as hard as it possibly could.
This leads to what I beleive to be a clutching law : The more powerful your engine, the more aggressive the ramps in your clutch can be.
Correct????
One more question: There is clearly a difference in a 413 ramp compared to a 441 to a ______. With a helix the number that describes the helix refers to the angle (or angles) of the helix. I assume the numbers 441 refers to something as well. What is that something???
If anyone has anything has anything else to add, please do.
