clutching notes
Here is some notes that Geo posted a couple years ago about his findings on the m7 clutching. Maybe it will help answer some of you guy's questions.
MX
The D&D and Bikeman dyno sheets are slightly different. Mine feels like Bikeman is closer, kinda peaky, falling off on either side of 7400 to 7700rpm. Funny thing is with the final clutch set-up I chose, the sled started to feel real strong in the 6900 to 7400rpm. range like the exhaust valves started to open earlier. If you compare the D&D sheets from an '06 M7 to the '07 M8 (Crossfires actually) the M7 makes more power at 7800. Track speed is realative to the snow and load (hill) but my comparative numbers from the same hill (small about only a 15 sec. pull but steep, 2 sled length run in at the bottom) I have used for years are; #1: stock (68's, Yellow-white, 36 helix, orange rear) about 41, 42mph. at 7800 to 7860rpm. (about the same as every new sled I've had since 2000 700 doo Highmark); #2: AC recommendations for my altitude (70's, yellow white, 44/40, orange rear), about 43 to 44mph. at 7800 to 7840 (nice gain but the M7 pulled that combo to a higher track speed). Then I tried a softer front spring (AC red) to lower rpm with set-up #2, No change at peak rpm. (I was surprized) or track speed, but the engagement rpm dropped to 3000 rpm and the engine pulled it well (will be hard to get stuck with this soft a start, nice for me), meaning good rip when you want it. Then I tried a big helix I have (50/42) to lower rpm but the sled wouldn't pull the 50 (only 7350 rpm but held it) starting into the hill but it pulled about 45mph track speed. On the flats it created heat at higher speeds. Back to the 44/40. That was day one ( had to do some playing). Day two ( when I get into something I keep going till it's done). At home I changed wieghts to AC 73gr and reinstalled stock the yellow-white because I didn't think the engine would pull the Red spring. When I got to elevation ( about 5500ft), I took a rip across a fresh meadow ( about 2' fresh) and pulled high mph (65 to 70) and rpm about 7750 to 7780. Now we're getting some where but there was something missing in the 1/4 to 3/4 throttle range that I felt with the Red spring in. So I pulled in under one of my favourite old trees and changed to the Red spring. Now I'm at set-up #3;AC 73gr. wieghts, AC red primary spring, AC 44/40 helix and AC orange secondary spring installed at stock hieght. Off to the test hill with a little playing on the way. What a nice package this felt like. Part throttle donuts, wheeling out of creeks, instant track speed, and blurry top speed once you got up on the snow. Fun. Peak rpm. didn't change, 7750 to 7780. At the test hill I did a couple of runs to get #'s to write down then pulled under another good old tree to check clutch temps (not bad, for what I just did in the last 40min. actually pretty good) and record. This set-up pulled 44 to 46 mph at 7750 to 7780 rpm. Good steady shift (no stalls or stops in trackspeed). I was quite happy with this because I know on the bigger hills with more of a run at them it will pull a couple three more mph. Needing a break and because I wanted to try the 46/38 I brought, to see if the sled would pull the 46, I changed it out. Now, #4 set-up; same as #3 except with the AC46/38 helix. Put the stuff back in the pack and take a 10 min. tour to warm up before hitting Test Hill (it felt even stronger in the midrange and bottom). This time I was more surprised. The sled pulled through the 46 into the 38 easily and at a steady 7700 to 7720 rpm. (must have been slipping on the back a bit to lower the rpm. with a shallower helix) on the hill and across the meadows. Track speed on my hill increased to 49 to 51 mph. Top speed on the way back to the truck is everything rubbed off the primary and secondary sheaves (black majic marker marks) and it goes past 80mph way too fast. Clutches are as cool as anything I ever owned. All this is straight off my notes with chit chat between the lines. I've done a few more things with rear spring preload and relocating the helix depth to fine tune for me, but I ain't saying no more (it also doesn't make that much difference). I also went into as detailed a explanation as I could so people don't PM me to ask "what do I use at this elevation with this set-up", 'cause I don't know. This is what works awesome for me and my stock sled at my elevation (to tune for higher elevations try spring before reducing wieght). Hope it helps some. Geo.
Might as well try some clutching on the M8, took the cat clutch tool box to the woods for testing, really don't have good hill yet, but checking some perameters. M8 153 ddy pipe, stock clean belt clutches, 4500-6000 ft al. 1 been too revy since break in, was thinking more weight , hit it........ goes to 8000 and backs down to 78-7900 I think to much. yarded out the stock 68 grm put in 70grm heavy tip, forgot to write down part number in book. But pulled better, starting to wheelie a little, pulling harder but no real change in RPM 2. put in cat #710 73grm I cut to 71.5 last year, this is the lighter tip heavier butt. Punchier in mid, feeling better, still no real RPM difference, feels smoother though at low mid throttle, I think loading the motor some. 3. put in uncut 73 grm 710, more improvement, got to be a little more carefull on trails, launching through some bumps ratched the track, pulling hard, wot hits 8000 still, only place to load its in powder, still to revy 7800 +. So I went up 5 grams, a trail animal now, just got to wait for better climbing conditions to see sustained 20 sec. loads. But for the sake of "tried it", 73 gram weights and put in the short red Cat primary spring that Geo tried, interesting.........about 3400 engagement and the 800 pulls it great off idle, even put it out in the crap, pulls it no hesitation, what a great trail set up for gas mileage and cruising with little throttle, but made the sled lazy, no chance of launching off trail bumps, but with only a 240 or so shift out it pulls 7700 any place I put it on the bar in the powder, you'de think it would drop rpm dramaticlly, didn't.
