I’d like to start by thanking Straightline for their excellent lake ice run video showing the tachometer and speedometer. The reference to their video in this post is designed to be analytical and not critical of their work. https://www.youtube.com/watch?v=cLQ...3916&feature=player_embedded&x-yt-cl=85027636
There has been a lot of talk about using the tach recall function to gauge what your clutching RPM is. I tend to disagree with this method. What this method is doing is catching any sort of spike that may occur be it on a launch, or at the climb at the end of the shift on a top speed run. It always seems to come back significantly higher than the normal observed numbers. It is hard to watch the tach while driving. When running various clutching setups if my sled runs in the 8600 range I will often see recalls on the order of 8900. When it runs in the 8800 range I will see recalls on the order of 9100.
Watching the Straightline video I see a characteristic that I have seen in my sled as well. If you watch in the early to mid part of the run, you’ll see RPM come up, pull back, come up, pull back then come up again. This is on the order of 8900, 8360, 8800, 8400, 8800 then it seems to settle in and run in the 8800-8900 range before eventually climbing to 9100 range. To my novice eye what I am seeing is that during the 8400-8800 oscillation either the clutch is under/over shifting, or there is a belt slip of some sort going on or both? Once past this window in the 40-60 mph range the RPM stabilizes quite a bit. Then as it crosses 100 mph and we hit the end of the shift, the RPM stabilizes even further while it still climbs steadily to peak. To me the sled is clutched to the 8800-8900 range. My guess is that a recall with be on the order of 9200+
I see the same oscillation after launch with my sled. Then the RPM stabilizes somewhat and tends to hold in this window. What I don’t see with my sled is the RPM climb at the end of the shift. I suspect this will come as the break in continues and as I find better conditions with less drag.
So my questions:
What is causing the RPM fluctuations, particularly the 40-60 mph ones? I’ve never ran the stock clutching to see what the MPH was, but it seems that this is a tamed down version of what the stock clutching does when it hits the limiter shortly after a launch.
Why is it so hard to keep the RPM in a nice narrow window like a typical 2 stroke where you would expect to see the needle of a tach hidden behind a narrow strip of tape?
There has been a lot of talk about using the tach recall function to gauge what your clutching RPM is. I tend to disagree with this method. What this method is doing is catching any sort of spike that may occur be it on a launch, or at the climb at the end of the shift on a top speed run. It always seems to come back significantly higher than the normal observed numbers. It is hard to watch the tach while driving. When running various clutching setups if my sled runs in the 8600 range I will often see recalls on the order of 8900. When it runs in the 8800 range I will see recalls on the order of 9100.
Watching the Straightline video I see a characteristic that I have seen in my sled as well. If you watch in the early to mid part of the run, you’ll see RPM come up, pull back, come up, pull back then come up again. This is on the order of 8900, 8360, 8800, 8400, 8800 then it seems to settle in and run in the 8800-8900 range before eventually climbing to 9100 range. To my novice eye what I am seeing is that during the 8400-8800 oscillation either the clutch is under/over shifting, or there is a belt slip of some sort going on or both? Once past this window in the 40-60 mph range the RPM stabilizes quite a bit. Then as it crosses 100 mph and we hit the end of the shift, the RPM stabilizes even further while it still climbs steadily to peak. To me the sled is clutched to the 8800-8900 range. My guess is that a recall with be on the order of 9200+
I see the same oscillation after launch with my sled. Then the RPM stabilizes somewhat and tends to hold in this window. What I don’t see with my sled is the RPM climb at the end of the shift. I suspect this will come as the break in continues and as I find better conditions with less drag.
So my questions:
What is causing the RPM fluctuations, particularly the 40-60 mph ones? I’ve never ran the stock clutching to see what the MPH was, but it seems that this is a tamed down version of what the stock clutching does when it hits the limiter shortly after a launch.
Why is it so hard to keep the RPM in a nice narrow window like a typical 2 stroke where you would expect to see the needle of a tach hidden behind a narrow strip of tape?
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