Interesting power graph compares Doo and Poo engines.

Matte Murder

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Saw this in the Poo section, interesting comments from the math challenged. You can see how much more power the Doo makes in the middle, close to 20 hp at the same rpm. This is why you can ride a Doo at 1/4 to 1/2 throttle and get a lot of work done lol.
 

kiliki

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date in the lower corner.... who's still in break in....
would love to see the torque graph and who when to the dealer first for repairs....
 

jonsonfire81

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Does anybody have a similar graph for the new Ctec 800 or Zuke to compare? Maybe overlay that graph with these?

The seat of my pants test is confirmed by this graph. Rode all of the new sleds over the last few months and they all feel really close. Great times we live in right now! Unless the sled you buy is a complete lemon, you have 3 great sleds to choose from.
 

User Name

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Can someone explain why more power at a lower RPM is better?

It looks to me like they have very similar peak hp. And a CVT allows the gear ratio to change to maintain a desired RPM if that's the case, why does it matter what RPM it's at? Seems to me it should be a question of what the highest peak hp is balanced with the smoothness of the power curve.
 

NHRoadking

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Can someone explain why more power at a lower RPM is better?

It looks to me like they have very similar peak hp. And a CVT allows the gear ratio to change to maintain a desired RPM if that's the case, why does it matter what RPM it's at? Seems to me it should be a question of what the highest peak hp is balanced with the smoothness of the power curve.
Having more power available with less RPM means the motor is not working as hard.
 

off trail mike

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So there is a 250RPM +/- spread between the poo and the doo for any given HP right to max really. It's definitely noticeable having ridden both for a long time. Also suggests the doo motor will be more durable...but 850 doo has the highest piston speed in industry so time will tell on that front.

I think part of that is the the 10cc difference (850 vs 840) and more about doo choosing a longer stroke engine which produces more torque at any given RPM.

Will it make much difference when we ride? Not really. You can change ramp profile and clutch to match either power bands.

The doo is definitely faster revving but the poo has a more linear powerband which is a benefit in tight technical trees. Both have their place.

OTM
 

Big10inch

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Saw this in the Poo section, interesting comments from the math challenged. You can see how much more power the Doo makes in the middle, close to 20 hp at the same rpm. This is why you can ride a Doo at 1/4 to 1/2 throttle and get a lot of work done lol.
I think you might be the one a little confused as to how this all works. First you are trying to equate rpm and throttle position. You do understand that the graph represents WOT at all points. So if you are making 20 extra hp at 6500 rpm it is not at a lesser throttle opening, it is wide open.

The only real difference is the rpm it is making the power at. The person in the other thread that said the curves match except the rpm was correct. The only difference between the two is that the Poo requires an extra 2-300 rpm at any given point to make the same power.

It has also been correctly stated that this is all a wash when both are geared and clutched correctly. They really make the same power, the Doo looks a little fatter through the midrange but that again could go either way with regards to how the power feels based on clutching.
 

donbrown

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Can someone explain why more power at a lower RPM is better?

It looks to me like they have very similar peak hp. And a CVT allows the gear ratio to change to maintain a desired RPM if that's the case, why does it matter what RPM it's at? Seems to me it should be a question of what the highest peak hp is balanced with the smoothness of the power curve.
Many / most don't ride WOT all the time.

More initial power on demand is a good thing … faster take off , more power to maneuver around obstacles.

More power to the track at lower RPM helps … for instance more power in the trees with less track speed.
 

Big10inch

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Can someone explain why more power at a lower RPM is better?

It looks to me like they have very similar peak hp. And a CVT allows the gear ratio to change to maintain a desired RPM if that's the case, why does it matter what RPM it's at? Seems to me it should be a question of what the highest peak hp is balanced with the smoothness of the power curve.
It really doesn't matter. The irony is that the lower revving Doo motor has higher piston speeds than the higher revving Poo motor. So tell me again which is "working harder"? The Doo motor has a better design ie: stronger but a little heavier.

With each properly geared and clutched the 300 rpm difference in power peaks is really meaningless. On the snow I would bet on a good running 840 in most contests but, I have not seen it. I haven't seen an 840 on the snow even... Lighter and belt driven with a better track angle are all Poo advantages. Doo comes back with a reliable, powerful 850 engine, at least it seems so, so far.

It is rider preference, and the rider is likely to make the difference anymore. The top sleds are all awesome, each with their own issues but still all very impressive!
 

NoNonsense

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I think you might be the one a little confused as to how this all works. First you are trying to equate rpm and throttle position. You do understand that the graph represents WOT at all points. So if you are making 20 extra hp at 6500 rpm it is not at a lesser throttle opening, it is wide open.

The only real difference is the rpm it is making the power at. The person in the other thread that said the curves match except the rpm was correct. The only difference between the two is that the Poo requires an extra 2-300 rpm at any given point to make the same power.

It has also been correctly stated that this is all a wash when both are geared and clutched correctly. They really make the same power, the Doo looks a little fatter through the midrange but that again could go either way with regards to how the power feels based on clutching.
There's really no point, but here goes another attempt for my buddy Matte..

Engine A
Peak power of 165 HP at 8200 RPM
Torque = 105.7 ft-lb

Engine B
Peak Power of 165 HP at 7900 RPM
Torque = 109.7 ft-lb

Engine A and Engine B are powering Vehicle A and Vehicle B, respectively.

Both engines are running at peak power in heavy snow at a speed of 50 MPH, or a rotational track speed of 330 RPM.

Vehicle A requires a final drive ratio of 24.85:1
24.85 * 105.7 ft-lb = 2626 ft-lb of torque at the track


Vehicle B requires a final drive ratio of 23.94:1
23.94 * 109.7 ft-lb = 2626 ft-lb of torque at the track

This is how a torque path works through a driveline.

A CVT system is extremely good at reaching peak RPM quickly along a WOT power curve at the lowest ratio (high torque) and proceeding to upshift through higher ratios at peak power. If you are on and off the throttle constantly (like most people ride in the backcountry) then you hit your peak RPM in a fraction of a second if your clutching is right. Especially if you're off throttle, backshifting and punch the throttle when the belt isn't totally in tension. This is helped along with how low the inertia is on the newer engines. Regardless of the CVT, if your final gear ratio is correct, you are still getting the same torque to the track along a similarly shaped power curve.

Maybe you're right and the Doo is a lot better at part throttle, I have no idea, but that has more to do with the stroke and port design in a 2 stroke. No one has part throttle data to look at, but regardless, full throttle performance will be very similar between the two assuming the rest of the transmission is working correctly.
 
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Ski-doo#1

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True: Doo makes more HP at any given RPM between the three sleds up to max RPM rating where of course the sleds fall off

What the graph really shows and what the true statement above really boils down to... is that the Doo consistently is making more torque since it is making the same power as the Poo at a lower RPM.
 
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willjogervais

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True: Doo makes more HP at any given RPM between the three sleds up to max RPM rating where of course the sleds fall off

What the graph really shows and what the true statement above really boils down to... is that the Doo consistently is making more torque since it is making the same power as the Poo at a lower RPM.
what happens after the doo's max rpm rating? do the other sleds just bow down and say go doo? We can't rev anymore or it's not fair? Probably not. Skidoo has a great motor but it's not a powerhouse compared to the other two. Cat's 800 is damn close to either and I'd be hard pressed not to say it's as torque-y (bad grammar-it's late) as the 850 skidoo. I'm not knocking the 850 by any means, but I feel like you are missing the point here. Clutch for your motor's powerband. It might make more torque at a lower rpm but if both sleds are clutched right the polaris will just be running 300 rpm higher and they both will pull hard. I've spent time on all three and they are all fantastic.
 

Big10inch

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True: Doo makes more HP at any given RPM between the three sleds up to max RPM rating where of course the sleds fall off

What the graph really shows and what the true statement above really boils down to... is that the Doo consistently is making more torque since it is making the same power as the Poo at a lower RPM.
So what I think you should do next is post up the torque curves. Then I want to see your sled pull itself around at 5000 rpm where the torque is greatest... More torque in a high strung 8000 rpm 2 stroke is mostly worthless. Clutching and gearing can easily compensate for the few extra lb/ft you think you have.

I agree, Doo made a pretty good motor this time around. Is it head and shoulders above the rest? Not from my experience, not even close.
 

shockman

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I would like to see more discussion on fuel injection, as I believe there is not a lot of secrets on how to make HP from a 2-stroke engine. I follow the evolution of sleds closely and read between the lines quite well. If I was to lay under the pickups in my driveway (3 brands) I would have trouble telling them apart, same as when I look at the sno-x sleds, I can't tell them apart. By the way all chassis on the snow come from the race sled. The one thing I have not seen patent poaching on is fuel injection. Polaris did it years ago and got sued by a small private guy who after several years and lots of $ finally won and P paid big.
The Doo engine I believe is making more power in the mid RPM range because of fuel injection.
BRP bought Johnson, I believe, to get FICHT patent's and quickly found they needed to change it a bit to work at higher RPM's as the outboard world needed only 7000RPM
:juggle:
 

winter brew

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The CVT (properly tuned) does cater to the power produced, but the bottom line is they all have to run from engagement to peak RPM. The more power made from engagement to peak can shorten that time and allow a quicker acceleration. A electric motor would be a extreme example of this...peak power from 0-whatever RPM. Think a peaky 440 spinning a big track vs a 800 making similar peak HP. In my experience on a mountain sled, it's all about making as much power as early as possible which also makes clutching more forgiving.
Then factor in the clutches/calibration and how they grip the belt at various ratios will also effect how ANY power is transferred. Maybe the Poo clutches do a better job than the Doo and show more power to the track at lower ratios? I have not seen much track dyno data to say. These graphs are just one factor between crank and snow.
 
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