Testing this weekend before the heavy rains began we discovered some interesting things.

The originel setup turns 7800 and flashes there in about 1 second. The rpm holds for the entirety of the rest of the run. The clutches are cool (105 deg) and the ambient temp is 70 deg. I made some ramps with a little more drop in the beginning but the same profile after about 1/3 shift.

Test with new ramps:

Sled leaves line good but after about 15 feet the sled bogs down. The tach reaches full rpm in about 100 ft and holds perfect there. I check the clock and the time is .5 sec slower, clutches are screamin hot. I wrap the secondary a little tighter and no gain. I try a lower finnish angle on the helix and there is a little gain but still .3 seconds off the original setup. After using a reverse helix with low numbers (43-47) reverse, the sleds comes close to the previous best but still 1 tenth off

The interesting part of this whole process is the TACH is showing the exact curve I am looking for yet the time is slow and the clutches are hot. The reason I say the "curve I am looking for" is because I need a little more load in the biginning and that is what I got. However sometimes theory gets thrown right out the window.

I found the problem can you???

GLH

i would try the next higher primary spring , (finish). i asphalt race too and i have a real hard time getting my primary to run cool. your problem that you went through is the problem i have most of the time , it comes out then drops a little then recovers , but not all of the time, i think if it spins a little it is causing the drop and i really don't like to tighten up the sec anymore than it is cause i want it to shift easier up top

Since you found the solution I won't take a stab at it, you probably know more about clutching than me anyway? But let me add that unless there is absolutly no traction whatsoever the belt is ALWAYS going to slip until the secondary catches up with the primary. Its a matter of gear reduction (or lack of it) at take off. During this period of slip time the secondary has a pretty good hold on the belt because of the mechanical effect of more sheave contact and the helix function. So given the belt WILL slip in the primary, what do you think will create more heat in the belt? a slipping sheave that is grabbing hard? or one that is grabbing lightly? In designing your ramp profiles you need to keep this effect in mind. Consider your gearing, traction and engagment rpm to estimate the slip period, gearing and rpm are the ez calculation, traction has to reasoned (aspahlt snow grass track size etc). The trick is get the ramp to load when the slip period is done. Any sooner and you have more heat.

Test 1
Ramp "A"
7800
Flashes 1 sec.
7800 Straight to finish
Pretension "1"
Time "X" seconds
Cool clutch
Helix - "1"

Changed Ramp - Ramp "B" [More aggressive start than original/blends to same profile after 1/3]

Test 2
*Ramp "B"
Low rpm off line until 100'
100' = 7800 rpm
Pretension "1"
Time "X" - .05 seconds
Hot clutch
Helix - "1"

*Increased pretension to Pretension "2"

Test 3
Ramp "B"
Low rpm off line until 100'
100' = 7800 rpm
Pretension "2"
Time "X" - .05 seconds
Hot clutch
Helix - "1"

*Changed Helix to helix "2"

Test 4
Ramp "B"
Low rpm off line until 100'
100' = 7800 rpm
Pretension "2"
Time "X" - .03 seconds
Hot clutch
Helix "2"


Hmm....I kinda got lost from your description of the events.
Im having a difficult time trying to figure out what you don't like?
Yes, obvious its the time that is lower than original....but Im confused with your notes. "sorry"
Umm, I dont think you are spinning. My experience is that when you spin, it is due to have a very large helix angle for start and / or the suspension is too rigid and does not transfer the chassis properly.
The engine will hit the peak, track speed is faster than sled speed, traction increases engine pulls down then climbs back up.
But in this here you loaded the primary arm with a steeper ramp to make the engine labor. The engine is not laboring from hooking up after a spin.

I know that pretension has great effect on top end and can prolong an engine from falling off when the speed is high. The pretension can save you from the TRA arm in the primary pushing too hard at highest speeds. "band-aid fix"...lower angle number would be better approaching the point on the helix where you lose engine rpm. MHO

All I am really concerned about is that you said "Cool clutches", then "hot clutches"
Hot should be from belt spin...more spin than before. The "clamp" is lost due to friction being poor.
This could be from the helix angle being too large on the big end or the secondary spring does not have enough final compressed force to clamp the belt and have good friction to keep the sheaves cool.

I give up on this one. Not enough, or the right information for me. :(

what glh has done is made a more eggressive ramp at engagement and now the belt is heating up , why? duno , but it should go better out of the hole right? that theory crap goes again.what ramp did you ruin?lol . If you get more agressive it is going to spin (period) and when you spin it upshifts right?then it hooks in the wrong gear resulting in bog.

:D Damon, my guess would be that you need to "load" (spring, or pin weight) the motor more, or use a straight angle helix. May even be the belt deflection, or clutch alignment also. Just for giggles throw in a brand new secondary spring and primary. That is about it. I forgot to add, drop the ramps first, and put the old ones back in. Too much of a "dip" in the ramp. I know that you know how to clutch, but I should add what you already know. Change one little thing at a time, not all of the above. :)

just a guess

if you made a deeper "stall" notch on the bigining with the same primary spring, the clutch will of course need turn turn faster before engagement, right. now if your belt is being held hard by the secondary set up , when the primary does engage it will surely spin more on the belt, thus the heat, if the belt is too hard to get a grip with more friction with the new "stall" notch in the ramp. rpm's are good, then so is the arms, and ramp profile.

just in the begining, first 15 seconds??

try a new primary spring with a little less initial tension and equal final tension as the one you used, to work better with the engagement notch you put in the ramp.

how close am i??

GLH...With the ramps, by a little more drop in the beginning, do you mean that you made a new set of ramps tha start higher in the beginning and blend into the old ramp profile at 1/3? Or did you take the same ramps, leave the start height the same, drop down a little quicker at first, then blend in at 1/3? The ramp profile description from one to the next is a little confusing to me.

Sounds like ramps are causing the primary to bind at engagement to the 15 ft mark, then it overshifts causing bog.

Sorry I am a little vague on the description of what happened. I wanted the share the results without sharing the info.

The new ramp is the same height and profile as the old ramp. The beginning is taller and much more drop. I was trying to get a little better 10-12 ft ET's. This is only accomplished by the primary. The spring is the same as well as the rest of the setup. I had to change to a lower helix just to recover some lost rpm.

Many things have happened which I did not explaine. I was trying to convey this:

2 ramps are exactly the same except for the first 1/3 shift. My ramp is taller with a steeper hill in the beginning. I would expect the engine to bog a little on takeoff because of the drop, which is what I wanted. I would also expect the rest of the shift curve to be the same. That is where I was wrong.

ANSWER: The answer to this unorthadox question is this:

The ramp I created allowed so much upshift in the first 10 ft that the tention on the belt went south. The primary was so far ahead of the secondary that it never caught up. This was helped somewhat by giong to a stiffer secondary spring setting as well as lower initial angle on the helix. I had a hard time understanding what was happening at first but after a little slow motion thinking I remember feeling the sled fight itself. Trying over and over again to feel what was happening I finally discovered the light chatter marks in the secondary. A little slippage in that big sheave causes a ton of heat.

For the next test sesion I have made another set of ramps that are not as tall at the beginning to slow the upshift a little in the first 10 ft.

Although there are many ways to achieve this I prefer to play with ramp profile for this type of problem.

GLH

I love this stuff.


Good info!!

GLH... sure you wouldn't like to share some more?

Like to grind your own eh? just for the heck of it dig out a polaris 10-, hold it up to some of your tra ramps.

Moved by request.

I hope we get some new comers to our new Tech Discussion Area.

Iddoski,

You know I love to help with setup info but I must keep this setup quiet. To much on the line this year. :)

Hillpounder,

Yes, alot of the ramps in the TRA are the same profile of the polaris 10-... weights. The best part is being able to dustribute mass indifferent places easily.

GLH