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View Full Version : Rpms that are difficult to recover..."Summit's



Dynamo^Joe
August 17th, 2007, 08:40 PM
was on clickers 3 with x pin wt. Worked the clickers to 6 which was constant improvement but still off.
Dropped flywt, set clickers to 3: Same problem! Worked clickers up to 5 but not any better.

Did not want to back shift. Seemed to pull good when I got the rpms up to 8000 but getting there was a problem.

If you get rpms that are difficult to recover when cycling the throttle...

Then
Test and pick the clicker you like the best...
Look at helix finish angle, what is it?....
Leave every other clutching detail alone and only lower finish angle on helix.

The primary is pushing too hard for the helix angle that is being utilzed at that moment/speed along the shift curve for the condition you are driving in.
So you think to yourself:
"Darn, but the sled is getting mushy here" You think with questions "Too low of clicker?...Too much pinweight?"

Consider:
"What angle is the button or roller pressing on the helix?"
"What angle am I utilizing at this moment?"
"Could I use a larger helix angle?...or a lower angle at this point/speed which my sled feels sluggish at?"

To improve recovery rpms, make the secondary resist the push from the primary by "stalling" the shift. The upshift is stalled, you let the engine pick up rpms again.

Chew on Theory:
*Large angles produce great upshift/smaller angles produce great backshift.
*Large angles produce low belt clamp forces/smaller angles produce increased belt clamp forces.
*Belt slip = heat production
Knowing those 3 details could you not think you would want to apply a "required angle" for the speed or shift ratio the sled is at? A more required angle to provide an engine rpm that follows your thumbtip?

A little tidbit from the inertia dyno at ECP in CT.
02~05 800 Doo's. The hotter the pipe gets on continuous pulls/testing the more lbs torque the engine loses between 4700~7450 rpms however for a gain in peak hp. The hotter the exh pipe gets if you were to see the torque curve on a graph, the curve shifts to the right towards higher rpms making larger peak hp gain but for a loss of torque in the midrange rpms.
Do a dyno run with ice cold rags on the pipe the peak hp is a disaster but the torque 500 rpms below known peak is monster.

The events in the snow; You reduce the throttle position, the rpms come down to say 5000+. With a pipe that is hotter than previous runs, the torque may be down 4~5 lbs less than a cooler pipe and with too large of a helix angle at that point, you would require a smaller angle to keep the engine maintaining proper rpms. With the torque loss you increase the throttle again and the engine should accelerate from that 5000 rpms to 7850 rpms?......no, you find the engine could only accelerate from 5000 to say 7000?....7200? or if and when the engine gets to 7850 it took a long time to get to peak rpms.
You find the response is slow, the engine labors back to peak rpms, if...it...can...get...there.

To prove this...
If you were to turn around and go back to the start position, let the exhaust pipe cool off, the repeat the exercise by cycling the throttle at the same point along the run, the engine will be more responsive.

The first thing to do is when you see this event you mention regarding "soggy response".....stop, pop the hood and check the secondary temperature, compare to primary temperature. Measure on sheave faces.

The temperature is the clutch telling the tuner that the system is not being efficient. The warmer temperature is a result of the belt slipping through the secondary sheaves.
The non-destructive testing portion of my job, I have to take temp readings on industrial motors. I used a laser temp gun to measure. I went around and so called "calibrated" my hand touch in "seconds" to the motor temps.
The other two guys in my job use the touch method also and find it quite accurate.

Touching hand on metal:
130 deg F = 5 seconds or more
140 deg F = 4 seconds to "ouch"
150 deg F = 2 seconds to "ouch"
160 deg F = 1 second to BLISTER!

If you have hot clutches then there is belt slip. Why belt slip? Lack of spring force or lack of a more required helix angle to provide improved clamp; missing out on improved backshift and engine response.

An example for lack of better numbers...
A tuner seeing poor throttle response using a 48/44 would improve the throttle response using a 48/40

Regarding a secondary spring...
A tuner seeing poor throttle response using a 200/300 would improve the throttle response using a 225/300

The Clutch sheaves will clamp the belt harder, lowering clutch sheave temperatures.
The increased force in the secondary will stall the upshift, forcing the engine to produce higher more correct rpms.

Sledderglen
August 17th, 2007, 08:58 PM
Lets hope that BRP has worked out the issues from the XRS last season.

Summitric
August 17th, 2007, 09:42 PM
Welcome Aboard, Joe Imhoff..... Good To See You Made A Quick Splash On This Site Too. This Site Should Benefit You As Well, And I Will Be E-mailing You The Info For The Clutch I Want To Order. Check Out The Pics And Video Arcade Sections.... Pretty Cool Too. Again, Welcome Aboard Dynamo Joe!!!!:)

Lost
August 18th, 2007, 01:12 PM
Welcome Lord Joey every sled that I have has your kits in them and all are great. When can I order a kit for my XP 163 is the new secondary as much of pain to work on as it looks.

Shredder
August 18th, 2007, 09:10 PM
Welcome aboard DJ. I will be calling you this week, to complete my order for the kit we dicussed thru Email. I just brought the RT home and I'm already itchin' to tear the clutches apart. :)

MtnCrazy
November 9th, 2007, 05:11 PM
Wow very good read!!! Thanks...