Want to hear about anyone that is running lightweight rotating parts like titanium clutch bolts, lightweight clutch covers, etc. Does it make a noticeable difference?
Rotating weight reduction
- Thread starter Bauer112
- Start date
Yeah thats for sure, but is it worth it?
By the way I'm asking for more of the performance gained in engine response rather than just weight
Normal everyday guy i dont think will notice. I did an aluminum recoil cup, w/ti bolts and the cut brake rotor from PES and i didnt really notice. But i did them over the summer and did an x3 track too so i overall added rotating mass
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I guess the answer to that.... is your wallet too heavy now?
Reducing engine rotating weight always helps. But the things that help the most are pistons, rods, pins, and crankshaft. Thats where you actually notice gains. The things like flywheels, starter cups, clutch cover/bolts dont really make that much difference and certainly not enough to feel or notice. The parts in the first list are heavy parts that have to change directions. The second list are lighter parts, closer to the center of rotation and are always rotating in the same plane.
The place you will get the biggest gain in loss of rotating weight is the track. Its 40-60lbs thats always getting sped up and slowed down. Take 10lbs off a track and you know it right away. Can you get too light with a track?!?!?!, I think so, and I think we might find the limit to that this season. Eric
I noticed a difference in engine response when i installed a carbon primary cover and titanium bolts (primary ended up 1.25lbs lighter than stock). Was it worth it? not really sure, depends how much extra cash you have. The track is the place to start for sure.
I'm making a few changes in this area this season, as well as adding boost. I am doing them all at once, so I won't be able to report on individual changes, but here are some photos documenting the weight difference for those who are looking into it.
Stock 163" 3" paddle, 3" pitch
Conquer 280 2.8" paddle, 3.5" pitch (I weighed it again with the shrink wrap and strapping removed and it weighed an even 42#)
Stock 6 tooth, 3" pitch
Avid Products Extroverts 6 tooth, 3.5" pitch.
So, all said and done, a 12.4 lb loss of rotating mass.
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Stock 163" 3" paddle, 3" pitch
Conquer 280 2.8" paddle, 3.5" pitch (I weighed it again with the shrink wrap and strapping removed and it weighed an even 42#)
Stock 6 tooth, 3" pitch
Avid Products Extroverts 6 tooth, 3.5" pitch.
So, all said and done, a 12.4 lb loss of rotating mass.
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Thanks for the feedback guys. Keep me posted on your results when you get your changes on the snow. I am for sure considering the conquer track, would just like to hear a little more about it once people really start riding it and not sure whether to stick with the 2.86" pitch or change drivers. I have a 155 2.6 track with sidekick but was also considering the lightweight clutch covers and things like that but have not heard if they really make much of a difference.
Seems easier and cheaper power to get the BD "boost button".
From an engineering perspective, the reflected inertia of all the drive train components and overall weight of the sled, back to the motor crank shaft is a function of 1/gear ratio squared. This plus the inertia of the crank and primary clutch determines the overall inertia of the sled. When the primary clutch first engages and hasn't started shifting, the sled theoretically accelerates the fastest as the reflected inertia is the lowest because the gear ratio is high. At this point about 7% of the motor torque goes to accelerating the crank and primary clutch, 1.5% goes to the secondary, 90% goes to the sled, and the other 1.5% is the other drive train components. I did this analysis by estimating the weight of all the drive train components with the weight of the sled and rider at 600 lbs. Once the primary flashes to shift speed (8000 rpm) the inertia of the crank doesn't matter anymore as it stops changing speed. So from there on 97% of acceleration of the sled is determined by the weight of the sled and rider. (and power of course)
When I first got my 2016 AXIS 800 rmk with the lighter weight crank I could definitely feel the difference in throttle response and acceleration at initial takeoff. This makes sense given my analysis. Reducing primary clutch weight like bolts and covers will make a difference in how it feels up until it starts to shift then it will be gone.
Reducing the weight of any other rotating components from the secondary to the track drivers makes almost no difference (>0.5%). From there the weight of the sled is coupled to the track as long as the track is not slipping. Therefore the rotating inertia of the track is the track plus the weight of the sled. They are not considered separate in my analysis. If you reduce the overall weight of the sled by 10% you will increase the acceleration by 10%. To get that 10% is tuff as in this example the sled and rider is 600 lbs so you have to reduce 60 lbs.
Adding 10% more power is much easier. If you can do both like burandt, then you got something.
Cinno
When I first got my 2016 AXIS 800 rmk with the lighter weight crank I could definitely feel the difference in throttle response and acceleration at initial takeoff. This makes sense given my analysis. Reducing primary clutch weight like bolts and covers will make a difference in how it feels up until it starts to shift then it will be gone.
Reducing the weight of any other rotating components from the secondary to the track drivers makes almost no difference (>0.5%). From there the weight of the sled is coupled to the track as long as the track is not slipping. Therefore the rotating inertia of the track is the track plus the weight of the sled. They are not considered separate in my analysis. If you reduce the overall weight of the sled by 10% you will increase the acceleration by 10%. To get that 10% is tuff as in this example the sled and rider is 600 lbs so you have to reduce 60 lbs.
Adding 10% more power is much easier. If you can do both like burandt, then you got something.
Cinno
You're going all out. And did you weigh your wallet before and after?
Ha! It gets lighter, but I keep filling it back up!
You're going all out. And did you weigh your wallet before and after?
Ha! It gets lighter, but I keep filling it back up!
I see you've resurfaced. This is something I do not believe your qualified to comment on. These guys pay for their parts.Nothing new for a sledhead
Great thread guys with great info. Remember it all adds up, even the little things. Unfortunately these days with the OEM's doing their homework the $100/# era is long gone.
Dan
Thats a whole lot of math you did there. In my experience, several of your calculations dont work out to real world results. Have you ever spent anytime on an engine dyno, and then a chassis dyno to see where your figures come from? Then making drive line changes to lighter parts to see loss or gain? I have done both of those things, several times, with snowmobiles and race cars. Did you know that only about 50-60% of the hp at the crank shaft makes it to the track?
Further more, this statement..... "Once the primary flashes to shift speed (8000 rpm) the inertia of the crank doesn't matter anymore as it stops changing speed." What stopped changing speeds? the fly weights in the clutch?
Or this statement.... "Reducing the weight of any other rotating components from the secondary to the track drivers makes almost no difference (>0.5%). From there the weight of the sled is coupled to the track as long as the track is not slipping" Again, this doesnt make any sense at all. Of course the track is slipping, and every single part in that drive line will make a difference. Eric
A lot of questions and comments here. Let me clarify a few issues. The drive train components have mass but there rotational inertia is a function of there shape. So the jackshaft is heavy but it has a small diameter so its rotational inertia is small. The brake rotor is relatively light but its diameter is large so it has a relatively higher rotational inertia. These components are all part of the sled and have to be accelerated linearly by the track. So there are losses due to there rotational inertia and by the fact there base weight is sitting in the sled. The sled is accelerated by the track. The track has rotational inertia but because it has the sled sitting on it, the reflected track inertia back to the motor is track weight plus sled weight. You can't separate the two. If the track slips in the snow the track speed runs away as there is no weight attached. So reducing track weight has no more effect than reducing sled weight in other ways like lighter seats, a-arms, skids, etc.
Another thing about rotational inertia is you have to reflect it back to the motor to determine the effect it has on acceleration. The rotational inertia of the brake rotor maybe similar to the bottom gear in the chaincase but because of the bottom gear has a ~2.5 gear ratio its reflected inertia back to the top gear is 1/2.5 squared or only 0.16 as much as the top gear. So if you want to put some money into lowering rotational inertia you lower the brake rotor. I stand by my previous comments that most of the rotational inertia of the drive train components don't matter, including the track. The exception was that light weight crank Polaris added to the Axis, that was good.
I had a CMX (crazy mtn extreme) sled in the day and I was amazed by how they reduced sled weight. Its all in the details. You go after the big ones first then 100 small ones. CMX would cut off the exposed threads from every bolt on the sled. Many they redesigned to make smaller in diameter to reduce weight. Thinner tunnel metal. Hence the 20K price. Cinno
That wouldn't improve the engine response though.
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