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Discussion Starter · #1 ·
A get a bad over rev in the first 1 second of my runs. See attached scan of graph. I've had the weights tucked, and untucked. Big sheave clearance or little. It just doesn't seem to grab the belt. I've used the 020, and now trying the XS. I can move this line up and down(more or less arm weight), but it always seems to be the same shape. I'm gonna try a steeper initial helix angle(60-50 now), but think I may end up sucking the belt in the secondary.

Any idea's?
 

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Steeper initial would be my first guess also. Neat stuff you have there!
 

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I've been down that road with that helix you mentioned, and a 62/50. My experience was that it will suck the belt down into the secondary. The over rev in that part of the run is more that likely a clutch alignment issue and/or engine movement at the initial hit. It could also be that your current helix is sucking the belt into the secondary. GOOD LUCK.
 

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I'm running a 60/40 on mine....You got that motor strapped down good? -Had some simmilar problems with mine too. The big twins just seem to hit the belt real hard. Tight clearance on the primary helps alot too. What do you have for data aquisition? Digitron? That's what I'm running now-Nice setup eh'?
 

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Discussion Starter · #6 ·
Track spin should be minimal as its got chisels and not trenching(busting some ice chucks out maybe).

Motor should be sitting pretty tight as I have a sno-tech monster mount in there, and the snubber it tight to the motor.

The 60/40 seems like it would keep my revs higher on the big end. Tight belt clearances would make it engage with less snap, and slip more no?

Running a digitron, but this model doesn't support a jackshaft sensor, which would be helpful.
 

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Discussion Starter · #8 ·
Dan, the gears this weekend were 24/39, but on New Years they were 25/38, and last year they were 26/41. Doesn't matter the gear or the weights, the shape of the curve always remains the same, maybe higher or lower depending on weights, but same shape. It's really that first one second. If i roll it on, its perfect goes right to the rpm and stays there. I dunno
 

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Discussion Starter · #10 ·
9 tooth drivers yep. Do you mean a 62/54 helix, or do you mean it should pull either a 62 or a 64 starting angle?

Got a 62/54 to try, probably need to lighten up the weights to keep the same finish rpm, with that which is a can do.
 

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try it, won't hurt to try.. I would leave it, see what happens, then just get the correct helix.. ending less if need be
 

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Don't believe it is sucking the belt into the clutch, that would cause a bog. Try a 021 belt, softer compound than the 020, we used that on grass with the F7 with good success, but no long runs, it will get very soft, stretch, and bad things will happen.
 

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<div class='quotetop'>QUOTE (ZR1000 @ Jan 16 2007, 09:33 PM) <{POST_SNAPBACK}></div>
Dan, the gears this weekend were 24/39, but on New Years they were 25/38, and last year they were 26/41. Doesn't matter the gear or the weights, the shape of the curve always remains the same, maybe higher or lower depending on weights, but same shape. It's really that first one second. If i roll it on, its perfect goes right to the rpm and stays there. I dunno[/b]
Your shift curve is very indicative of tall gearing. The engine is overpowering the belt grip under hard acceleration when you hammer the throttle. When you roll into the throttle your shift curve is flat. We fight that speed running all the time.

You might want to try scuffing your clutches with more than just scotch brite pads or take some gear out. Softer belt wouldn't hurt either.
 

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I AGREE WITH THE SOFT COMPOUND BELT THEORY. I HAVE FOUGHT WITH THAT SAME INITIAL OVER REV ON FIRECATS FOR A WHILE MYSELF. SOME GUYS RUN THE SPEEDWERX 5406 SOFT COMPOUND BELT TO HELP THIS. BUT I HAVE ALSO SEEN GUYS GO FAST WITH THE 021 CAT BELT THE REALLY FAST CAT GUYS WILL TELL YA IF YOU CAN KEEP THE RPMS DOWN AROUND 7200-7400 OUT OF THE HOLE THIS WILL BUILD HEAT IN THE PIPE AND MAKE IT MPH LIKE HELL ON THE BIG END. THE FIRECATS ARE TORQUEY ENOUGH TO ENGAGE AROUND 46 TO 4700 AND STILL 60' WELL. GOOD LUCK!!!!!
 

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Discussion Starter · #17 ·
<div class='quotetop'>QUOTE (catattack57 @ Jan 20 2007, 11:22 AM) <{POST_SNAPBACK}></div>
Don't believe it is sucking the belt into the clutch, that would cause a bog. Try a 021 belt, softer compound than the 020, we used that on grass with the F7 with good success, but no long runs, it will get very soft, stretch, and bad things will happen.[/b]
I don't think its sucking the belt either. I got ahold of the 021, and worked a few different helixs. Seems to be coming around. Did get one belt warm on a few back to back runs, and it evaporated. Poof.


<div class='quotetop'>QUOTE (sjhauge @ Jan 21 2007, 07:13 AM) <{POST_SNAPBACK}></div>
<div class='quotetop'>QUOTE (ZR1000 @ Jan 16 2007, 09:33 PM) <{POST_SNAPBACK}>
Dan, the gears this weekend were 24/39, but on New Years they were 25/38, and last year they were 26/41. Doesn't matter the gear or the weights, the shape of the curve always remains the same, maybe higher or lower depending on weights, but same shape. It's really that first one second. If i roll it on, its perfect goes right to the rpm and stays there. I dunno[/b]
Your shift curve is very indicative of tall gearing. The engine is overpowering the belt grip under hard acceleration when you hammer the throttle. When you roll into the throttle your shift curve is flat. We fight that speed running all the time.

You might want to try scuffing your clutches with more than just scotch brite pads or take some gear out. Softer belt wouldn't hurt either.
[/b][/quote]

Will try scuffing a bit more aggressively, I really need to give it a bit more gear. Started with 24/39, went to 24/38. Still need more gear I think.


<div class='quotetop'>QUOTE (MARKQF6 @ Jan 21 2007, 08:07 AM) <{POST_SNAPBACK}></div>
I AGREE WITH THE SOFT COMPOUND BELT THEORY. I HAVE FOUGHT WITH THAT SAME INITIAL OVER REV ON FIRECATS FOR A WHILE MYSELF. SOME GUYS RUN THE SPEEDWERX 5406 SOFT COMPOUND BELT TO HELP THIS. BUT I HAVE ALSO SEEN GUYS GO FAST WITH THE 021 CAT BELT THE REALLY FAST CAT GUYS WILL TELL YA IF YOU CAN KEEP THE RPMS DOWN AROUND 7200-7400 OUT OF THE HOLE THIS WILL BUILD HEAT IN THE PIPE AND MAKE IT MPH LIKE HELL ON THE BIG END. THE FIRECATS ARE TORQUEY ENOUGH TO ENGAGE AROUND 46 TO 4700 AND STILL 60' WELL. GOOD LUCK!!!!![/b]
I'd love to find a way to get it to grunt at 7400. My engagement is low around 3600, and would like to raise it some, but now running a 200 initial rate. Whats next, notched weights?

Thanks to all who have replied, I really appreciate you sharing your experience and insight.
 

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Seems as I have read in one of the cat performance manuals that changing the gearing actually has the opposite effect from what you would think. Say you have the 25/39 in there, you change to a 25/38 thinking that the rpms will drop, the load sensing characteristics of the torque converter (driven) will actually raise engine rpms. In effect, if you want to lower the rpms, you would want to go to a lower overall ratio. On the grass, our F7 would only turn 7650 rpm with 19/43 gearing (10 tooth drivers), a .441 ratio, but with a 19/41 (.463), same belt, weights, helix, springs, would turn very close to 7800 rpm. Just more food for thought. Also, if you are running a spring with that much pretension, gong to a notched weight, with a lesser starting rate spring may also help ease the early over-rev. Good Luck!
 

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<div class='quotetop'>QUOTE (ZR1000 @ Jan 22 2007, 12:46 PM) <{POST_SNAPBACK}></div>
<div class='quotetop'>QUOTE (catattack57 @ Jan 20 2007, 11:22 AM) <{POST_SNAPBACK}>
Don't believe it is sucking the belt into the clutch, that would cause a bog. Try a 021 belt, softer compound than the 020, we used that on grass with the F7 with good success, but no long runs, it will get very soft, stretch, and bad things will happen.[/b]
I don't think its sucking the belt either. I got ahold of the 021, and worked a few different helixs. Seems to be coming around. Did get one belt warm on a few back to back runs, and it evaporated. Poof.


<div class='quotetop'>QUOTE (sjhauge @ Jan 21 2007, 07:13 AM) <{POST_SNAPBACK}></div>
<div class='quotetop'>QUOTE (ZR1000 @ Jan 16 2007, 09:33 PM) <{POST_SNAPBACK}>
Dan, the gears this weekend were 24/39, but on New Years they were 25/38, and last year they were 26/41. Doesn't matter the gear or the weights, the shape of the curve always remains the same, maybe higher or lower depending on weights, but same shape. It's really that first one second. If i roll it on, its perfect goes right to the rpm and stays there. I dunno[/b]
Your shift curve is very indicative of tall gearing. The engine is overpowering the belt grip under hard acceleration when you hammer the throttle. When you roll into the throttle your shift curve is flat. We fight that speed running all the time.

You might want to try scuffing your clutches with more than just scotch brite pads or take some gear out. Softer belt wouldn't hurt either.
[/b][/quote]

Will try scuffing a bit more aggressively, I really need to give it a bit more gear. Started with 24/39, went to 24/38. Still need more gear I think.


<div class='quotetop'>QUOTE (MARKQF6 @ Jan 21 2007, 08:07 AM) <{POST_SNAPBACK}></div>
I AGREE WITH THE SOFT COMPOUND BELT THEORY. I HAVE FOUGHT WITH THAT SAME INITIAL OVER REV ON FIRECATS FOR A WHILE MYSELF. SOME GUYS RUN THE SPEEDWERX 5406 SOFT COMPOUND BELT TO HELP THIS. BUT I HAVE ALSO SEEN GUYS GO FAST WITH THE 021 CAT BELT THE REALLY FAST CAT GUYS WILL TELL YA IF YOU CAN KEEP THE RPMS DOWN AROUND 7200-7400 OUT OF THE HOLE THIS WILL BUILD HEAT IN THE PIPE AND MAKE IT MPH LIKE HELL ON THE BIG END. THE FIRECATS ARE TORQUEY ENOUGH TO ENGAGE AROUND 46 TO 4700 AND STILL 60' WELL. GOOD LUCK!!!!![/b]
I'd love to find a way to get it to grunt at 7400. My engagement is low around 3600, and would like to raise it some, but now running a 200 initial rate. Whats next, notched weights?

Thanks to all who have replied, I really appreciate you sharing your experience and insight.
[/b][/quote]

What is your belt clearance in the primary? Sounds like it is VERY tight. Are your weights on the rollers ?

What weights are you running ?
 

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<div class='quotetop'>QUOTE (catattack57 @ Jan 23 2007, 06:30 PM) <{POST_SNAPBACK}></div>
Seems as I have read in one of the cat performance manuals that changing the gearing actually has the opposite effect from what you would think. Say you have the 25/39 in there, you change to a 25/38 thinking that the rpms will drop, the load sensing characteristics of the torque converter (driven) will actually raise engine rpms. In effect, if you want to lower the rpms, you would want to go to a lower overall ratio. On the grass, our F7 would only turn 7650 rpm with 19/43 gearing (10 tooth drivers), a .441 ratio, but with a 19/41 (.463), same belt, weights, helix, springs, would turn very close to 7800 rpm.



Just more food for thought[/b]
Glad to see someone's paying attention,,, it's amazing how many have this bass-ackwards, I get to deal with this at the parts counter and on the phone every day at work bang your head


That is the nutrition this sport needs slaphappy
 
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