Lets just explore o.d for a minute here and look at some things that go into it, when your into o.d. in a clutch you are putting the belt up as high as possible in the front clutch and down all the way in the rear clutch. This puts the belt in a very tight radius in the rear clutch. We all know that the tighter you bend something like a belt or a track the more force is required to turn that item in a tighter radius, means your gonna take more hp from the engine to complete that turn. Try it, take a spare belt and putting your hand on top, roll it on a table top so the radius is the same in both ends, rolls pretty easy doesnt it, now push the one end down till the belt has a small 3-4" radius, alot harder to move along isnt it? You also increase belt speed tremendously in overdrive, ever gone down the lake and had a belt blow right at speed? this is most likley due to excessive belt speed! The faster the belt speed, the greater the loss of clamping power is thats being applied to the belt. the manufacture takes this into consideration when setting up the gearing of the sleds we buy, they want to keep belt speeds down for increased belt life and safety from exploding belts from excessive belt speed, which in turn adds heat to the clutchs and belt and shortens their life. This heat comes from the added friction of turning the belt in a tight radius. This goes the same as increasing the rpm of the engine, its alot harder to clutch effectively a engine running at 10,200rpm then one at 8000rpm!
When your looking at drivetrain efficiency, the belt is not very efficient at low speeds, because the belt is only grabbed by a very small radius in the front clutch, as the clutch shifts the belt is raised in the front allowing a longer section of belt to be grabbed. A easy way to see this right in front of your own eyes is simply take a white paint marker and mark your belt the entire area thats touching the front sheaves at rest, take it off and measure it. Now open up your secondary clutch and slip the belt about halfway down in the rear clutch, this will give you extra slack in the front and you can raise the belt up to the midway point of the front clutch. Now look at your marks from before, when the belt is in a larger porting of the front clutch, youve more then doubled the area you grab, same thing goes into overdrive as its just reversed. Why would you not want to clamp the most belt area possible with both the front and rear clutch??
High clutch efficiency is free power!
1;1 clutch ratio is approx. 10% more efficent then being into overdrive. This varys as some clutchs can move the belt more then others, the size of the front sheaves determines this. Example being a bearcat front clutch is larger in O.d. and can move the belt alot higher into overdrive then say a yamaha primary can. So the ratio can be even more then 10%
Using Aaens example: Speed runs and drag racers are interested in good topend,thier machines are usually lighter with with bigger engines, these machines end up being geared about 25% taller then the speed they actually can reach, if they are shooting for 110mph they may actually be geared for 130mph. The reasons being if you look at clutch effiency curves you will see that the efficency drops the further into overdrive you are, to get maximum topend you need as much hp as possible from the engine!! If 1:1 ratio is 10 percent more efficent then o.d. is you would attain more topend mph by gearing tall and never getting into overdrive, your applying more power to the track below overdrive . If the sled had 100hp engine 1;1 would give you 90hp applied to the driven clutch, with overdrive youd only have 80hp!!!!!
If anyone has read Olav Aaens book of clutching you can read all about this information. The clutch efficiency charts make for some good reading and they are definitely something to think about, you can try the basic examples with a belt and see how the logic applies to this exactly.
When your looking at drivetrain efficiency, the belt is not very efficient at low speeds, because the belt is only grabbed by a very small radius in the front clutch, as the clutch shifts the belt is raised in the front allowing a longer section of belt to be grabbed. A easy way to see this right in front of your own eyes is simply take a white paint marker and mark your belt the entire area thats touching the front sheaves at rest, take it off and measure it. Now open up your secondary clutch and slip the belt about halfway down in the rear clutch, this will give you extra slack in the front and you can raise the belt up to the midway point of the front clutch. Now look at your marks from before, when the belt is in a larger porting of the front clutch, youve more then doubled the area you grab, same thing goes into overdrive as its just reversed. Why would you not want to clamp the most belt area possible with both the front and rear clutch??
High clutch efficiency is free power!
1;1 clutch ratio is approx. 10% more efficent then being into overdrive. This varys as some clutchs can move the belt more then others, the size of the front sheaves determines this. Example being a bearcat front clutch is larger in O.d. and can move the belt alot higher into overdrive then say a yamaha primary can. So the ratio can be even more then 10%
Using Aaens example: Speed runs and drag racers are interested in good topend,thier machines are usually lighter with with bigger engines, these machines end up being geared about 25% taller then the speed they actually can reach, if they are shooting for 110mph they may actually be geared for 130mph. The reasons being if you look at clutch effiency curves you will see that the efficency drops the further into overdrive you are, to get maximum topend you need as much hp as possible from the engine!! If 1:1 ratio is 10 percent more efficent then o.d. is you would attain more topend mph by gearing tall and never getting into overdrive, your applying more power to the track below overdrive . If the sled had 100hp engine 1;1 would give you 90hp applied to the driven clutch, with overdrive youd only have 80hp!!!!!
If anyone has read Olav Aaens book of clutching you can read all about this information. The clutch efficiency charts make for some good reading and they are definitely something to think about, you can try the basic examples with a belt and see how the logic applies to this exactly.
Mac
Member
Overdrive Yes or NO?
MrViper - I’m only guessing here… but thinking that with all the theory about the loss of efficiency your opinion is that nothing can be gained with overdrive. I would like to know if you would agree that our clutches could be bottoming out. I’m certain mine is. If that were the case would your recommendation be to just gear taller. Would you recommend gearing taller than my sled may be able to achieve? My thinking is I could benefit with lower gearing and still have OD for the few times a day I could take advantage of the speed.
MrViper - I’m only guessing here… but thinking that with all the theory about the loss of efficiency your opinion is that nothing can be gained with overdrive. I would like to know if you would agree that our clutches could be bottoming out. I’m certain mine is. If that were the case would your recommendation be to just gear taller. Would you recommend gearing taller than my sled may be able to achieve? My thinking is I could benefit with lower gearing and still have OD for the few times a day I could take advantage of the speed.
Nobody said its the "only way"
I think it was best said by srxmagic "theres more then 1 way to skin a snake", however, you may be able to get the same speed result or close to it, but being in a more efficient ratio will put MORE POWER to the ground, so your gain could be or will be more. What would be the result in srxmagics example not getting into overdrive and doing things differntly, 126,127,128mph? no one knows till you try it! Buffalobob likes to run overdrive, if thats what works for him, great. I just am trying to put out some information to let people see theres always more then 1 option to get to a desired result.
I would personally run taller gears, I will tell you that it does take MORE motor horsepower to pull taller gears, BUT you will also gain more mph if that makes sense to you. If you have a "healthy" engine taller gears will be faster. I would suggest reading Olav Aaens clutching book, then reread the book again to absorb the information, some of the information can be a little much to all sink in at 1 time. Then applying the information in the field will then yield the desired results.
I was able to yield 127mph out of my 02 srx on a lake here, trail ridden sled,not a race set up speed run sled, stock, and not all slammed down. I did have oversize wheels in the skid frame along with 7.5" rears, chaincase gearing in which I ran on the trail, my own clutching combo and helix. It was verified by the Ohio State highway patrol. He was watching us playing on the lake from the state park parking lot where we had parked our trucks and trailers and we asked if he would want to shoot us with the new laser radar, he was kinda into sleds I am guessing and with a chuckle,agreed. So we had a blast one afternoon playing and after 2 minor secondary spring adjustments,(less secondary twist) I pulled the biggest mph of the day on my 3rd attempt. The next closest mph was a 99 srx with 118mph, might have almost hit 120mph, I dont remember as he made alot of runs. Followed by a zr900 and a f7, I think both of which were around 113-115mph.
We were running across the bay, I would have to only guess at the distance, we didnt measure it off we were just initially playing around, maybe about 1500-2000ft long, a decent ways across. It was not real great conditions as the snow was hard and kinda bumpy with glare ice spots in the middle from the wind cleaning off the snow. I think with a few other applied set ups, I could have hit 129-130mph?? maybe, maybe not??.
All I am trying to say is I applied these things from the clutching book and learned ALOT more by asphalt racing, where you can see the results of your clutching to the time slips, 60,330,660,1000, 1320ft marks, every change you make shows up the very next pass!! Its then very easy to get a grasp at to whats taking place in the clutch's.
All in all do whatever you feel the most comfortable with, but research the effects of both ways, read the book then go out in the field and try things till you get the results you want. Everyone has thier own way of doing things, some just work better then others.
I think it was best said by srxmagic "theres more then 1 way to skin a snake", however, you may be able to get the same speed result or close to it, but being in a more efficient ratio will put MORE POWER to the ground, so your gain could be or will be more. What would be the result in srxmagics example not getting into overdrive and doing things differntly, 126,127,128mph? no one knows till you try it! Buffalobob likes to run overdrive, if thats what works for him, great. I just am trying to put out some information to let people see theres always more then 1 option to get to a desired result.
I would personally run taller gears, I will tell you that it does take MORE motor horsepower to pull taller gears, BUT you will also gain more mph if that makes sense to you. If you have a "healthy" engine taller gears will be faster. I would suggest reading Olav Aaens clutching book, then reread the book again to absorb the information, some of the information can be a little much to all sink in at 1 time. Then applying the information in the field will then yield the desired results.
I was able to yield 127mph out of my 02 srx on a lake here, trail ridden sled,not a race set up speed run sled, stock, and not all slammed down. I did have oversize wheels in the skid frame along with 7.5" rears, chaincase gearing in which I ran on the trail, my own clutching combo and helix. It was verified by the Ohio State highway patrol. He was watching us playing on the lake from the state park parking lot where we had parked our trucks and trailers and we asked if he would want to shoot us with the new laser radar, he was kinda into sleds I am guessing and with a chuckle,agreed. So we had a blast one afternoon playing and after 2 minor secondary spring adjustments,(less secondary twist) I pulled the biggest mph of the day on my 3rd attempt. The next closest mph was a 99 srx with 118mph, might have almost hit 120mph, I dont remember as he made alot of runs. Followed by a zr900 and a f7, I think both of which were around 113-115mph.
We were running across the bay, I would have to only guess at the distance, we didnt measure it off we were just initially playing around, maybe about 1500-2000ft long, a decent ways across. It was not real great conditions as the snow was hard and kinda bumpy with glare ice spots in the middle from the wind cleaning off the snow. I think with a few other applied set ups, I could have hit 129-130mph?? maybe, maybe not??.
All I am trying to say is I applied these things from the clutching book and learned ALOT more by asphalt racing, where you can see the results of your clutching to the time slips, 60,330,660,1000, 1320ft marks, every change you make shows up the very next pass!! Its then very easy to get a grasp at to whats taking place in the clutch's.
All in all do whatever you feel the most comfortable with, but research the effects of both ways, read the book then go out in the field and try things till you get the results you want. Everyone has thier own way of doing things, some just work better then others.
How were you able to get to those speeds with a 02 srx without the dcs going off?
AV fuel?
AV fuel?
richer jetting, and 100 octane fuel mixed with 94 pump fuel.
I grass raced the same sled with 45 pilots and 135 mains on straight 100 octane fuel, the light would only just start to blink the last 20ft of the track.
I grass raced the same sled with 45 pilots and 135 mains on straight 100 octane fuel, the light would only just start to blink the last 20ft of the track.
I think I read somewhere that you used some nylontape? to isolate the sensor slightly? Could I do this, because I think the sensor might be a little too sensitive, or shouldn't I?
Theoreticly could a piped viper being the same HP as a stock SRX achieve the same results or close while maintaining a descent trail set up?
justaviper, yes it could, the viper with pipes has alot of potential, they can be a force to be reckoned with if done up properly.
see post to answer your question on if you should buy one....
http://www.totallyamaha.net/forums/showthread.php?p=265366#post265366
http://www.totallyamaha.net/forums/showthread.php?p=265366#post265366
bufalobob
Member
mrviper:
the test is flawed!
the reason for overdrive clutching is to gear down to improve both bottom end & midrange acceleration & keep top end speed. if he would have changed gears the graph would have been much different!
i've never used a speed sheave so i can't speak for how they work - but from what i understand pat hauck has used it for years & he's probably won more races than all of us on this site put together. ski doo clutches are 17% overdrive fom the factory.
there is a lot more to overdrive clutching than just slapping on a speed sheave. like any other performace mod it is a complete package which may require both front & rear clutch changes & definitly gearing.
bob
the test is flawed!
the reason for overdrive clutching is to gear down to improve both bottom end & midrange acceleration & keep top end speed. if he would have changed gears the graph would have been much different!
i've never used a speed sheave so i can't speak for how they work - but from what i understand pat hauck has used it for years & he's probably won more races than all of us on this site put together. ski doo clutches are 17% overdrive fom the factory.
there is a lot more to overdrive clutching than just slapping on a speed sheave. like any other performace mod it is a complete package which may require both front & rear clutch changes & definitly gearing.
bob
Bob,I knew someone would bring this up. Its a valid point ,but ,you could also change the gearing in the stock sheave as well and change the graph, but your constant is still the same. You can move the graph up or down by the gearing, by installing lower gearing it will show more hp at the beginning and less at the end, but the same will apply to the stock sheave as well if you were to change the gearing.
What I am trying to get across is the power transmitted to the track, keeping the gearing the same was just to make the test simple and equal, you can change the gearing in both and get higher readings at the beginning or end of the run, just simply depends upon the ratio used in the chaincase.
As far as the Hauck comment, well ...I will just say" YA", he has won a lot of races, a few of races he has been DQ'd at also for not meeting tech, no further comments needed.
What I am trying to get across is the power transmitted to the track, keeping the gearing the same was just to make the test simple and equal, you can change the gearing in both and get higher readings at the beginning or end of the run, just simply depends upon the ratio used in the chaincase.
As far as the Hauck comment, well ...I will just say" YA", he has won a lot of races, a few of races he has been DQ'd at also for not meeting tech, no further comments needed.
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Great post
When can I borrow Aaens clutching book from you Don?
Madmatt
When can I borrow Aaens clutching book from you Don?
Madmatt
bufalobob
Member
mrviper:
simple laws of physics - a body in motion tends to stay in motion & a body at rest tends to stay at rest. you need more h.p. to accelerate an object than you do to keep it moving. car manufacturers have been doing this for years not only with overdrive but now with alternate cylinder firing.
i have spent countless hours working with overdriving yamaha primarys & ad-vantage secondarys both racing ( radar & timers ) & trail riding. works great for me & everyone else i have shared my results with.
bob
simple laws of physics - a body in motion tends to stay in motion & a body at rest tends to stay at rest. you need more h.p. to accelerate an object than you do to keep it moving. car manufacturers have been doing this for years not only with overdrive but now with alternate cylinder firing.
i have spent countless hours working with overdriving yamaha primarys & ad-vantage secondarys both racing ( radar & timers ) & trail riding. works great for me & everyone else i have shared my results with.
bob
need torque to move something hp is gonna be a factor
for top speed
for top speed
Buffalobob, The car manufactures are worried about gas MPG, not speed! Thats why the engines drop to smaller sizes and we have overdrive transmissions, running the engines at lower rpms are also helpfull for emissions!! Automobile wet clutch auto /manual transmissions/engines are alot more efficient in running then a varible belt drive snowmobile transmission. If the snowmobile trans was so good why isnt it in a car?, a motorcycle ? a truck? only snowmobiles and some atv's use them. Its because they are not effective or better say efficient enough for anything else, they work so good on a snowmobile because of the constant changing loads applied to the chassis/track from inclines, snow drifts, starting and stopping etc. but its hardly a vehical set in motion stays in motion phenomina. If that were the case then just let off the gas once at 80mph, why does the sled coast down rapidly in mph?? should stay in motion by your example... because the sled also has great percentages of parasetic losses from the tracks rotation/drag to the chaincase, all these systems eat up power, they are parasetic drag example #1 forefront.
Horsepower is the measurement of torq x rpm divided by 5252, if we only need to move a object to get it rolling and keep it rolling then all you need is hp which again comes from the torq which actually does the work of moving the object! Torq measured at the crankshaft is the twisting force at the crank expressed in pounds force foot, also known as foot pounds. So if we have a engine producing 20 lbs ft it means it moves a load of 20lbs with a lever 1 ft long connected to the crank. If the engine moves this load in 1 revolution then work is being done. So in this example: 126ft/lb (twisting force revolution x revolutions x lever length x torq), the hp carries the load once the torq has moved it from stationary, so your mph is always indictive of your hp!!!!
Want a current snowmobile example? how about any current pro asphalt sled, they are running 150-160/170mph in the 1/4 mile, this is only possible with lots and lots of topend hp from the large 1500+ cc engines and the turbo charged 4 strokes. Now if you start to diminish the hp applied to the track on topend the mph will be the first thing to drop, the et will suffer later but current 60 ft times and such have a giant effect on your elapsed time, however your mph is still again indictive of your hp from the engine, take away hp your mph will DROP!!
So how does all this apply to the clutch?? Easy, if we run in overdrive, the further into overdrive we go like your mention of 13-15% the MORE loss of power is shown/transmitted to the track/ground , power loss comes from the belt going thru its turning radius. The tighter the radius the higher the belt speed is also, the higher belt speed greater the loss of power again. The belt speed is controlled by engine rpm and the radius in which its bent. By pulling the belt lower in the secondary clutch, the sheave pressure is greater on the belt at the bottom of the sheaves angles and the results are high belt tension and constant loading and unloading of the belt as it tries to turn the tight radius, its pulled on the top and unloaded on the bottom, this allows the belt to creep along(slip) and increases friction which results in efficiency loss. Simply put your not clamping all the power you could be, your wasting power. With a larger radius you have more belt surface to grip, the more surface you grip the greater the hold. Why would you use a larger tire on a drag car if the stock one worked as good? The more surface you grip the greater the force can be transmitted!!
High belt speeds are what you get in high overdrive situations, also what causes blown belts!! I know you understand exactly what I am talking about as you mentioned to get a good clutch cover to run up in overdrive!! The manufacture gears thier sleds taller then what the machine is capable of for this very reason, slower belt speeds equal less blown belts and a more efficent working clutch, longer belt life from cooler running belts and slower belt speeds.
I know that there isnt any way to convince you could be mistaken, never is. This isnt meant to be a arguement starter either just trying to prove a point here. Sometimes one should open thier eyes as they might just gain something more they didnt know they already had, even more mph from putting more hp to the ground. I think Olav Aaen said it best:
"Knowing how to get maximum efficiency from your transmission puts MORE power to the ground!!"
Horsepower is the measurement of torq x rpm divided by 5252, if we only need to move a object to get it rolling and keep it rolling then all you need is hp which again comes from the torq which actually does the work of moving the object! Torq measured at the crankshaft is the twisting force at the crank expressed in pounds force foot, also known as foot pounds. So if we have a engine producing 20 lbs ft it means it moves a load of 20lbs with a lever 1 ft long connected to the crank. If the engine moves this load in 1 revolution then work is being done. So in this example: 126ft/lb (twisting force revolution x revolutions x lever length x torq), the hp carries the load once the torq has moved it from stationary, so your mph is always indictive of your hp!!!!
Want a current snowmobile example? how about any current pro asphalt sled, they are running 150-160/170mph in the 1/4 mile, this is only possible with lots and lots of topend hp from the large 1500+ cc engines and the turbo charged 4 strokes. Now if you start to diminish the hp applied to the track on topend the mph will be the first thing to drop, the et will suffer later but current 60 ft times and such have a giant effect on your elapsed time, however your mph is still again indictive of your hp from the engine, take away hp your mph will DROP!!
So how does all this apply to the clutch?? Easy, if we run in overdrive, the further into overdrive we go like your mention of 13-15% the MORE loss of power is shown/transmitted to the track/ground , power loss comes from the belt going thru its turning radius. The tighter the radius the higher the belt speed is also, the higher belt speed greater the loss of power again. The belt speed is controlled by engine rpm and the radius in which its bent. By pulling the belt lower in the secondary clutch, the sheave pressure is greater on the belt at the bottom of the sheaves angles and the results are high belt tension and constant loading and unloading of the belt as it tries to turn the tight radius, its pulled on the top and unloaded on the bottom, this allows the belt to creep along(slip) and increases friction which results in efficiency loss. Simply put your not clamping all the power you could be, your wasting power. With a larger radius you have more belt surface to grip, the more surface you grip the greater the hold. Why would you use a larger tire on a drag car if the stock one worked as good? The more surface you grip the greater the force can be transmitted!!
High belt speeds are what you get in high overdrive situations, also what causes blown belts!! I know you understand exactly what I am talking about as you mentioned to get a good clutch cover to run up in overdrive!! The manufacture gears thier sleds taller then what the machine is capable of for this very reason, slower belt speeds equal less blown belts and a more efficent working clutch, longer belt life from cooler running belts and slower belt speeds.
I know that there isnt any way to convince you could be mistaken, never is. This isnt meant to be a arguement starter either just trying to prove a point here. Sometimes one should open thier eyes as they might just gain something more they didnt know they already had, even more mph from putting more hp to the ground. I think Olav Aaen said it best:
"Knowing how to get maximum efficiency from your transmission puts MORE power to the ground!!"
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don, i dont think you are getting what bob is saying. you take two srxes, everything being the same, gear one down 1 tooth with overdrive cut in it. leave the other stock. the one with overdrive will beat the stock one. down the lake. if you are only doing top speed runs in a non timed or side by side race, the 1-1 is the best way to go. for racing with the guys on the lake od is better.
your clutching efficiency may be less in overdrive but when you figure in that you can now run less load on that clutch with lower gears it helps to even it out as well as give you a better bottom end.
your clutching efficiency may be less in overdrive but when you figure in that you can now run less load on that clutch with lower gears it helps to even it out as well as give you a better bottom end.
well they have cvt in our dodge car now and i can u let know that they realllllllllly sucks on gaz lollllllll ...cvt work like sled clutch
Scott, We already know that overdrive will lose approx. at least 10% of the power output, so if you have a 100hp engine , 1;1 will be about 90hp to the track in your example srx to the ground, running in overdrive youll be applying 80hp, so 80 hp would be faster then 90hp to the ground across the lake??? 
You need MAXIMUM HP to attain topend, down 10hp... your not going to beat the other at 90hp to the ground.
You need MAXIMUM HP to attain topend, down 10hp... your not going to beat the other at 90hp to the ground.
forgot one thing, when i say overdrive, im talking about either cutting .040-.070 out of the bottom or recutting sheave 1/2deg on each side. i do not recomend in any way the hauck sheave that makes one side of the clutch a different angle than the other. this makes the belt wear odd and causes binding, not the best way to achieve overdrive.
Mac
Member
Overdrive
Don in an example of a 1500 ft race geared one tooth lower wouldn’t our speed be faster for 1200 or 1300 ft prior to overdrive - then slowly becoming less efficient for the final 200. Could the benefits of a faster 1200 ft overcome the loss of HP in the final 200 ft? Also keep in mind the entire 200 is not all bad because the HP slowly falls off being at its worst accross the finish line.
Don in an example of a 1500 ft race geared one tooth lower wouldn’t our speed be faster for 1200 or 1300 ft prior to overdrive - then slowly becoming less efficient for the final 200. Could the benefits of a faster 1200 ft overcome the loss of HP in the final 200 ft? Also keep in mind the entire 200 is not all bad because the HP slowly falls off being at its worst accross the finish line.
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