Called several shops about clutching.
Most say 7950 to 8000
A couple say 7900 plus minus 50.
What do you say?
Most say 7950 to 8000
A couple say 7900 plus minus 50.
What do you say?
Optimal RPM
- Thread starter donbrown
- Start date
Rpm
7971 rpm on the dot no more no less!
7971 rpm on the dot no more no less!
Thank you for the precise concise number. Will the accuracy of the RPM meter allow such accuracy?
Called 4 shops yesterday.
Was interesting the ones I've done business for decades say leave it stock and use the existing clickers to get 7900. Only get a clutch kit if sled was modified.
Maybe change the spring and or helix to lessen the trenching by engaging at lower RPMS also helps backshift.
New shops I called said to get a kit and strive for 8000 RPM
Not uncommon to overrev peak to hit 8100 to 8300 and system retard starts at 8800 RPM?
Unfortunately a days drive away from snow with no time off really test the sleds with no miles
I've always shot for getting a little overrev on the flats (100-150 over peak) and let it work on the hills at 79-8000. No need to be any more precise than that, you have a tachometer that is not perfect, terrain that varies and engine output that varies with temp and altitude. That's the nice thing about a big twin, they have a fairly broad range of usable power.
Both the owners manual and a sticker on the clutch guard give you the optimum RPM which you can adjust up or down with the clickers on the clutch. The clicker comes on 3, increase the clicker up to the next number as you increase altitude as necessary or decrease the number to reduce RPM as you decrease in altitude.
If you find that your sled over revs at altitude you may need to add pivot weight or buy a clutch kit. Imo.
If you find that your sled over revs at altitude you may need to add pivot weight or buy a clutch kit. Imo.
Copied from a clutch website:
The #1 way to keep clutch heat to its lowest is to have correct engine speed when full throttle – 7900. Lower or higher than 7900 the temperatures soar. Both over or underrev, the belt ceases to move across the face of the primary clutch face.
Core Value - Lower heat by lowering part throttle engine speed. So when (example) poking along at 40mph on the hardpack, from this snow area to softer snow area, lower heat will be at 6200 rpms instead of 6700 rpms.
The #1 way to keep clutch heat to its lowest is to have correct engine speed when full throttle – 7900. Lower or higher than 7900 the temperatures soar. Both over or underrev, the belt ceases to move across the face of the primary clutch face.
Core Value - Lower heat by lowering part throttle engine speed. So when (example) poking along at 40mph on the hardpack, from this snow area to softer snow area, lower heat will be at 6200 rpms instead of 6700 rpms.
G
Here is a dyno that I've seen that varies slightly from the one previously posted. It's not mine.
peak power is 7950...
tach accuracy??
7900-8100 observed (never use recall) on a climb...
use back/back testing to verify if YOUR sled likes a certain TACH rpm...
-BJ
tach accuracy??
7900-8100 observed (never use recall) on a climb...
use back/back testing to verify if YOUR sled likes a certain TACH rpm...
-BJ
Ive talked to several clutch shops ... most say 7900 plus minus 50 is ideal
Very few have said 8000
You are over thinking it don. If your sled will run 7800-8000 when it’s working really hard like a climb in deep snow and you can get off the power and get right back there you have a great running sled. Oh, and if it doesn’t eat belts that’s a huge plus!
F
Peak engine HP is @ 7950. Does this mean when your tach says 7950, your engine is at 7950?
Dunno.
It might be. It might not. Each sled is a little different. It is up to the sled owner to fine tune which ever clutch kit they buy to their sled.
then they havent spent much time on a 850...
honestly, very few summits like 7900...
hot pipe, tach error (usually high), long pull, good can 8000-8100 is common-BJ
So how much tach error is in the 850 meter?
IS it "normal" amount of error?
Drive an economy vehicle for work ... MPH is off by 2-3 mph showing better gas mileage plus more distance driven to jobsites.
My contact at BRP says steady engine speed within 10 rpms on digital.
Below is a "Canned speech" every 850 customer gets in their kit information package; and/or anyone who asks me about 850 rated engine speed.
That "canned speech" is deliberate and framed from customer feedback, combined with knowledge I've sourced from the smarty of the smart-smarts dyno guy and his sidekick to help me; and personal firsthand knowledge.
[its not just me, i admit im not all knowing. Source the most competent in their field.] The smarty of the smart-smarts will also tell you what you see on the dyno for hp/rpms wont be the same out in the field.
Why I framed that "trials" speech is because I do know as you spend "X+" time at full throttle, pipe temperature increases; the power peak may move 50~100 rpms higher. Keep on the throttle with my kit and your pivot weight set for 7950, the engine speed climbs to 8000; which is great for "oh s4it" off/on throttle moments.
Im sure just bout' any of my customers would say "yup, that's how my 850 runs"
In the end the individual who's driving the sled knows what they like and what's best for themselves. There are guys who go into psychosis for getting 7900...to the opposite end "Huh? What tach?" haha.
When at full throttle you can hear, feel and taste the engine running at the right rpms for you - not by someone in front of a keyboard banging the gong... "thou shalt run at XXXX rpms you fool"
Make a run how you normally do, in your style. Change the pivot weight to change engine speed; see how you like it.
Sincerely,
I. Nfidel Flatlander :becky:
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