F500 has been roadracing the CVT for decades in the 105-110hp 800-850lb vehicle range in summer conditions and they survive fine. I have heard anecdotally of a belt letting go, but I cannot stress enough that it was put forth as a VERY rare event that happened because of an ignored obvious problem.
Just to clarify, I was talking about heat being created by belt slippage, not ambient temps.
It's typically due to abuse, but slippage will generate enough heat to smell it and see smoke rising off it in extreme cases.
CVTs in parallel, see DAF Variomatic
(yes, it had more going on beyond just 2x CVTs in parallel: functioned as a torque biasing diff plus the UV/CV joints)
https://grassrootsmotorsports.com/video/video-meet-variomatic-1950s-version-modern-cvt/
If you want something to drool over, Rotax has a webpage showing their complete engine lineup.
https://www.rotax.com/powertrains.html
Did anyone mention jetski/ PWC engines? There's a 1630cc supercharged 3-cyl with ~300hp weighing ~200#. It will have all of the same issues as a snowmobile engine if you want to adapt it to a car-type clutch and manual trans.
Can-Am's latest 'top of the line' SxS uses a dual-clutch trans rather than a belt CVT, but it also has an extra 40hp and weighs 400# more... and costs $14k more.
There are a few side-by-sides that don't have a CVT and they have a big reliability advantage because of it - apart from the Can-Am, Yamaha uses a sequential or single-clutch robotized manual in the YXZ1000R and Honda has a manually-shiftable slushbox in the Pioneer. SxS engines are generally similar to sportbike engines but built for lower revs and more torque. They also have an oiling system designed to run at crazy angles which would be a big advantage over a sportbike engine if used in a car.
So the PWC jet pump has to have thrust bearings, so that may be something that could be modified to make the coupling between engine and trans. Maybe torque tube with rear transaxle like a 944.
Pete. (l33t FS) said:In reply to Noddaz :
Aside from the potentially narrow powerband, if it's a 2 stroke then they really, really don't like it when you close the throttle at higher RPM. SAAB 2 stroke cars had a one way clutch on the transmission to prevent engine braking in order to save the engine.
Saab utilized a freewheel mechanism on their transmissions because of the particular way they handled engine lubrication. It was perhaps the best solution for Saab at that time. But it's not strictly a requirement nor concern for all 2 stroke engines. Meaning, people have solved this dilemma in various ways.
2 strokes are lubricated in a different manner than 4 stroke engines. Instead of utilizing a closed loop oil delivery system with a common sump and an oil pump to deliver lubrication to things like engine bearings and the underside of pistons for cooling effect, 2 strokes use a total loss oil delivery system and must either use premix (oil mixed in with the fuel) or an oil injection system that adds the correct amount of oil into the fuel-air mixture for a given engine load/ fuel requirement/ RPM. The amount of oil might be a fixed ratio, as in the case of premix that is delivered in a certain fuel:oil ratio like 32:1 or 40:1 no matter the RPM or engine load. Or it may be variable ratio in the case of oil injection systems that are typically dependent upon throttle position. Because of the way 2strokes are designed to divide the combustion cycle into phases, they utilize the crankcase in a manner (to pressurize the incoming air/fuel mixture) that prohibits closed loop oil recovery. Being total loss, the oil may be fully or partially combusted, and exits the tailpipe as smoke and/or oil vapor. This is oily smoke/ vapor is why they were so bad for emissions and essentially regulated out of existence.
When coasting or going down a hill with your foot off the gas pedal, the engine is operating in a low load, high vacuum, high rpm condition called "Over-run." Normally, there is little to no demand for fuel in this over-run condition. In a 2stroke, that means there is little to no fuel entering the engine, which can mean little to no oil lubrication or oil cooling. An engine can only tolerate that for so long before friction and heat causes catastrophic failure.
Most 2stroke gasoline engines, including the old Saabs, used analog carburetors to deliver fuel and oil in the right air:fuel:oil ratio for any given engine operating condition. They had different circuits in the carburetor to deliver the right amount of fuel-oil mix using throttle position as a surrogate for engine load. More oil actually leans out the air fuel mixture. So all 3 have to be optimized for all running conditions, if possible. But that's a tall order when using simple technologies like carburetors. If running premix oil lubrication, the oil ratio is fixed and therefore the oil amount is generally optimized for a certain engine operating condition or a narrow range of conditions (like maximum load). But that inherently means the oil amount is not optimized for other operating conditions like idle. On a road race engine that sees long periods of WOT it's not such a big deal as they don't spend a lot of time at idle or low rpm/ low load. But on a street engine, premix often delivers too much oil at idle in order to ensure there is also enough oil at high rpm, which can cause anything from poor emissions to poor performance. An excess amount of oil won't be fully combusted, and oil vapors can then build up inside the exhaust system and pour out the tailpipe.
Saab decided that the best approach for them at that time was to allow the driver to selectively disengage the transmission from the engine, thus allowing the engine to operate at idle speed and low load as the vehicle coasted down hill. In this condition, there was adequate oil to keep everything happy.
Many "modern" oil injected 2stroke engines allow a greater amount of oil to be injected even when the throttle is closed at high rpm. This can either be done using a cable splitter box that normally syncronizes the oil pump flow rate with the throttle position, and that also uses an electronic solenoid to override the oil pump cable under certain prescribed conditions. Or using a special electronically actuated "power jet" for oil injection, similar to the "power jets" that many GP bikes already use to allow for adequate fueling when ram air effects take over at higher vehicle speeds.
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