Well I have been jumping into my clutching as best I can with the cruddy winter this year. With really no snow to test on and a week up in Cochrane starting Sunday, I figure it might be money well spent to go pay Justin a visit down at FPP and get some time on his track dyno. I figure with his equipment, and more importantly his knowledge, I could probably improve my set up in far shorter time and far fewer belts than trying to accomplish the same thing out on the lakes - or at least that's my hope.
So I trailer down there. It's about an hour away from my house. Of course it was a mini snow storm and driving was less than ideal. I get there safe and they wheel the sled into his shop. I really had no idea how they did this. Turns out, they remove the rear suspension and in its place they install this flat skid that attaches to the front swing arm tunnel bolt holes and instead of idler wheels on the rear axle, there are a couple of drivers. The shaft that those drivers are on ultimately connects to the dyno input. Even with my M-20 with the air, they had it all swapped out in about an hour. They then wheel it outside to the dyno trailer. It's essentially and enclosed snowmobile trailer retrofitted with the dyno mechanism. Pretty slick set up.
So Justin does a first pull and I'm kinda freaking out inside. The sights and sounds of your sled being mashed to full throttle on this thing is scary as hell and amazing all at the same time. The first pull nets 110 track horsepower with a top speed of 121mph. The power curve looked good up to about 80-90 mph. After that there was a lot of peaks and valleys in the curve, which got worse as speeds rose. I was only building 9 pounds of boost so out came my laptop to dial in a bit more. The second pull hit 10psi and netted 112hp and a top speed of 125mph, but the same fluctuating power curve which seemed to concern Justin. After reviewing the run data, he said it looked as though I was getting some belt slipping at higher speeds. This may have been the culprit to my pulled cords a few weeks before. I'm running the STM 4 arm primary with 50 gram base weight cams with 14 grams in the heels and nothing in the mid or tips. He suggests I move more weight to the middle and tips to try and correct this. So I remove the cams to redistribute the weight and sure enough, the wear marks on the cam faces are really pronounced down at the heel but taper off to almost nothing at the tip, evidence of what Justin said was happening. After putting it back together, we make another pull. As it turns out, the data looks like Justin was correct. This run put me at 113 hp, but more importantly, it laid down 7-10 more track horsepower between 70mph all the way up to 131mph. Definite, tangible improvement. It even built more power down low, which was a bit surprising seeing as I lightened up the heel. Another plus was the erratic power curve on the top end was much more stable. All positive data.
The clutches were cool to the touch after each run too. As it turns out, I was getting close to having to leave, so this was the final run. Justin and his guys swapped my rear skid back in and had me loaded up and ready to head home in no time. All in all, it was a very cool experience. As he told me, I could spend days on that dyno wringing every last hp out of it, but in his opinion, the last set up showed greater efficiency and that I should run it a while and see how it goes. Next week will be the litmus test.
At the end of the day, I would highly recommend getting on a track dyno for this type of tuning. Justin figures I'm making about 245-250 hp at the crank. With the 1.5" track and trail studs, he figures this is a pretty good net track reading. The truth is, without the dyno, I would have never identified the 10 extra hp at the track. It's not the cheapest way to spend an afternoon, but to be able to transfer 10 more hp to the snow was more than worth it. This is the equivalent of adding 20hp at the motor, and we all know what that costs. The graph pictures show the 3 runs, with the red curve being the final improved set up.
![89abe69cfd68534c5ed0545e7227c5b3.jpg]( "89abe69cfd68534c5ed0545e7227c5b3.jpg")
![4403cfe64d840d494eb35caedbe55650.jpg]( "4403cfe64d840d494eb35caedbe55650.jpg")
![e8d653f8b517220780659299ce2d3168.jpg]( "e8d653f8b517220780659299ce2d3168.jpg")
![1f4b630d7aaac83058ff1598e7556fb2.jpg]( "1f4b630d7aaac83058ff1598e7556fb2.jpg")
![cce6d9baa829077131585fa9477dffb8.jpg]( "cce6d9baa829077131585fa9477dffb8.jpg")
![e47c08bae6d770d25e2aacb6e30418af.jpg]( "e47c08bae6d770d25e2aacb6e30418af.jpg")
Sent from my iPad using Tapatalk
So I trailer down there. It's about an hour away from my house. Of course it was a mini snow storm and driving was less than ideal. I get there safe and they wheel the sled into his shop. I really had no idea how they did this. Turns out, they remove the rear suspension and in its place they install this flat skid that attaches to the front swing arm tunnel bolt holes and instead of idler wheels on the rear axle, there are a couple of drivers. The shaft that those drivers are on ultimately connects to the dyno input. Even with my M-20 with the air, they had it all swapped out in about an hour. They then wheel it outside to the dyno trailer. It's essentially and enclosed snowmobile trailer retrofitted with the dyno mechanism. Pretty slick set up.
So Justin does a first pull and I'm kinda freaking out inside. The sights and sounds of your sled being mashed to full throttle on this thing is scary as hell and amazing all at the same time. The first pull nets 110 track horsepower with a top speed of 121mph. The power curve looked good up to about 80-90 mph. After that there was a lot of peaks and valleys in the curve, which got worse as speeds rose. I was only building 9 pounds of boost so out came my laptop to dial in a bit more. The second pull hit 10psi and netted 112hp and a top speed of 125mph, but the same fluctuating power curve which seemed to concern Justin. After reviewing the run data, he said it looked as though I was getting some belt slipping at higher speeds. This may have been the culprit to my pulled cords a few weeks before. I'm running the STM 4 arm primary with 50 gram base weight cams with 14 grams in the heels and nothing in the mid or tips. He suggests I move more weight to the middle and tips to try and correct this. So I remove the cams to redistribute the weight and sure enough, the wear marks on the cam faces are really pronounced down at the heel but taper off to almost nothing at the tip, evidence of what Justin said was happening. After putting it back together, we make another pull. As it turns out, the data looks like Justin was correct. This run put me at 113 hp, but more importantly, it laid down 7-10 more track horsepower between 70mph all the way up to 131mph. Definite, tangible improvement. It even built more power down low, which was a bit surprising seeing as I lightened up the heel. Another plus was the erratic power curve on the top end was much more stable. All positive data.
The clutches were cool to the touch after each run too. As it turns out, I was getting close to having to leave, so this was the final run. Justin and his guys swapped my rear skid back in and had me loaded up and ready to head home in no time. All in all, it was a very cool experience. As he told me, I could spend days on that dyno wringing every last hp out of it, but in his opinion, the last set up showed greater efficiency and that I should run it a while and see how it goes. Next week will be the litmus test.
At the end of the day, I would highly recommend getting on a track dyno for this type of tuning. Justin figures I'm making about 245-250 hp at the crank. With the 1.5" track and trail studs, he figures this is a pretty good net track reading. The truth is, without the dyno, I would have never identified the 10 extra hp at the track. It's not the cheapest way to spend an afternoon, but to be able to transfer 10 more hp to the snow was more than worth it. This is the equivalent of adding 20hp at the motor, and we all know what that costs. The graph pictures show the 3 runs, with the red curve being the final improved set up.
Sent from my iPad using Tapatalk
