General rule is longer the stroke the more torque an engine will generate at a lower RPM. Though HP will also be less at peak. Yes porting effect the entire equation but ignoring that and just looking at displacement in stroke vs bore.
So just generalizing by the bore and stroke given the Rotax should generate better torque at a lower RPM but with less overall HP.
The Polaris on the other hand, again generalizing by looking at specs will generate more HP but less overall torque.
Honestly HP mean's poop, torque is what pulls a big track in deep snow up hills, it also keeps you shifted and not back shifted.
But HP is what makes sales not so much torque.
General rule is longer the stroke the more torque an engine will generate at a lower RPM. Though HP will also be less at peak. Yes porting effect the entire equation but ignoring that and just looking at displacement in stroke vs bore.
So just generalizing by the bore and stroke given the Rotax should generate better torque at a lower RPM but with less overall HP.
The Polaris on the other hand, again generalizing by looking at specs will generate more HP but less overall torque.
Honestly HP mean's poop, torque is what pulls a big track in deep snow up hills, it also keeps you shifted and not back shifted.
But HP is what makes sales not so much torque.
Skidoo 82mm bore 80.4mm stroke
Polaris 85mm bore 75mm stroke
I think Polaris' shorter stroke moves the power band up the rpm range. But it also has just as much to do with porting, pipe and even intake configuration.
confusious saY when confused sTaY con fused ... HeY who lit the fuse ... i can help .. back in a bit /...i like the waY u THiNK ouT LouD ... beeP !! beep !!What they ^^^^ said (with caveats). Power is set by torque at a given RPM. You need to look at the dyno curves. These sleds typically hold their peak torque for a few hundred RPM and there is a small fluctuation in the numbers at that RPM, so it simply could have been the difference of half of a ft/lb at 8100 to 8500 rpm and they took 8500 instead of 8100.
Longer stroke will mean different port timing above and below the transfers and exhaust, which limits power output on the combustion stroke depending on where the exhaust valve opens and stops. Consider that these motors also have 2 different fuel delivery systems, one injects the fuel at the last minute under high pressure and the other is a case-induction motor which affects crank case pressure and case volume. Piston design, speed and rod angle are big items that will determine torque output since the combustion chamber design and bore diameter determine how fast the piston attains full speed on the combustion stroke. Bigger bore, longer combustion explosion (with all other variables the same). off the top of my head I don't remember the specific compression ratio of either motor or the piston and full rotating assembly weights. So many variables between them to measure and discuss. If you remember there was a piston reliability issue in the Liberty motor years back due to the rod angle putting too much pressure on the piston skirt. Spark plug angle and projection will also affect it. Consider that Doo has indexed the plugs. This allows for more even flame propagation across the cylinder and maybe allows them to start timing slightly earlier before TDC. Subtle differences like these can make the difference of the 3-4 HP or 2-3 ft/bs of torque that we are talking about between the 2 motors.
In 2019, Polaris had a different piston design with a thicker top half and also dropped a bunch of weight off the crank. Less rotational vibration with less weight. Thicker piston dome was likely to allow more casting for more dimensional stability and increased combustion heat dissipation to the cylinder, since they also re-vamped the cooling system at that time as well. The crank weight reduction was likely done to offset the increased piston weight. Thicker piston = Less heat in the piston (by transfer to the cylinder and then to cooling system) and less vibration on the crank means more reliability. All this is leading up to.........This motor has a 4 year warranty now.
Keep in mind the patent and warranty issues (see note about 4 yr warranty above). Simply building the same motor configuration as your competition will land you in court, even if it goes nowhere, the legal costs will still mount up and that bad press affects share price. Warranty claims and company write downs affect profit which affect share price.
Another thing is the amount of emissions that each motor can output. These companies are restricted on emissions outputs from a fleet level, so they need to manage cumulative emissions, which may mean a more restrictive exhaust on 1 brand vs another. Don't read into it too much. Usually the sales brochure spec is a little different than production. Many parameters change between the pre-production sleds and the mass produced, little changes like tweaks to fuel
Hope you're not more confused now than when we started.... LOL
Honestly HP mean's poop, torque is what pulls a big track in deep snow up hills, it also keeps you shifted and not back shifted.
But HP is what makes sales not so much torque.
If this statement was correct sleds would be running low speed boosted four strokes, or even diesels, because they both have way more torque than modern 2-strokes.
HP is the only true measure of an engines output. Torque only comes about in engine literature because that's how a dyno measures it, it puts a load on the engine (in the form of torque on the crank shaft) and uses the rpm to calculate power.
Sure different power curves may be easier to clutch for, but at the end of the day more hp wins.
Lund’s statement is correct....
What makes motorsports units exciting to ride, is their ability to make that power quickly. The current motors (regardless of 2S or 4S) is their power output compared to their weight. The power plant’s output per weight is important for the size of the chassis...
Diesels make good power, but their requirement to be physically constructed to handle extreme pressures are just not practical for Motorsport use.
Go ahead and mount an inline 6 Cummins in the chassis of your choice....!!
You completely misread my post. My point is that torque is not the be-all end-all specification for engine output. HP is all that matters. Torque really doesn't mean squat in a sled that has a CVT to utilize the peak power band. I used a diesel engine as an extreme example of this.
Torque isn't what moves a sled as was claimed, power does. Anyone that understands high-school physics understands this, power is the ability to do work, the more power the more work that can get done, or the faster the same amount of work gets done. Torque is solely the rotational force, at 0 rpm it does 0 work. Now when there is rotational movement with torque there is power, again power is the ability to do work.