DTSFab.com (Desert, Trail and Sand)
Automotive Powered Off Road (AKA: Buggys, Jeeps, Trucks, Etc,Etc. ) => Motor and Drivetrain => Topic started by: fabr on December 14, 2008, 02:47:49 PM
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I've been thinking about a post I saw elsewhere. It had to do with the reason for a CVT(constantly variable transmission) being desirable. The poster said it was always in the right gear.I agree but that brings up the question of is a cvt as beneficial on a larger,automotive engine/superbike engine as compared to a smaller 2 stroke or small 4 stroke engine.I don't see the need for a CVT or even the desirability on the larger engines with nice flat ,broad, torque bands as compared to a smaller engines narrower torque band.THe smaller engine I agree is likely to be best with a cvt . In other words WHO would think it beneficial to run a larger engine at peak torque(high rpms) for long periods of time.Seems very inefficient and unnecessary to me .
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The one thing I think you are missing based on the last question is that when you are cruising, torque load reduces and RPMs drop. The driven clutch is torque sensing.
I will choose a CVT up to as high a power as I can get clutches and belts to support it.
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I understand what you're saying. But as to how far you can go I'd think that at some point the belts would be the limiting factor . Personally I've driven both and will say that a blanket statement of I'll always choose one over the other is not IMO correct.Both have their pros and cons that will at times dictate one over the other.
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I have heard of a belt form aaenperformance support well over 350 hp. I will say like the ecotech and stuff, a cvt will ultimatley make a much smaller package, you could put one on a bus trans etc but then the length and weight double..
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Can't argue with that but it still doesn't make A CVT the best option for all uses.
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I dont believe the cvt is the best for all uses. In a minibuggy it is very well suited tho. ;D
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A well tuned CVT will make a power plant feel like it is twice the size and out put that it is...a poorly tuned CVT will kill a killer engine... the no-shift concept takes a pipey, unmanangable power plant...and make it drivable... example...165 horse tripple...zero bottom end grunt...CVT tuned to 6500 engagement...smokes the tires out of the hole...5000 engagement...little hard out of the hole but driveable thru the tight stuff...4800 engagement...doggy on hill-starts but easily powers thru the ugly stuff...Kinda like driving a stalled auto on the street, Belts, primary,secondary, shift pionts can be trickey ...but patients and some knowledge will get you thru- it...No shift in the woods is the only way to go...shifting and dodging trees can be a BITCH
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A well tuned CVT will make a power plant feel like it is twice the size and out put that it is...a poorly tuned CVT will kill a killer engine.. the no-shift concept takes a pipey, unmanangable power plant...and make it drivable... .example...165 horse tripple...zero bottom end grunt...CVT tuned to 6500 engagement...smokes the tires out of the hole...5000 engagement...little hard out of the hole but driveable thru the tight stuff...4800 engagement...doggy on hill-starts but easily powers thru the ugly stuff...Kinda like driving a stalled auto on the street, Belts, primary,secondary, shift pionts can be trickey ...but patients and some knowledge will get you thru- it...No shift in the woods is the only way to go...shifting and dodging trees can be a BITCH
I certainly agree with that most of the time.
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I have driven both in the sand and the woods
I like a fast back-shifting CVT and a hard mid-range hit power plant in the woods...In my opinion Cvt for the woods is the only way to go...Now on the Sand...That is another animal all together...I thought that the CVT sorta sucked...and liked driving the bike powered car...It was easier to me...to not up-shift the bike motor when I thought things were going to get hairy...Where the CVT wanted to back shift... altho that was my fault I had never had that buggy on the sand before, so it wasn't clutched for the sand and the constant drag that sand has...
Alot of people's woods riding is different than mine I range from branches slapping both sides of the cage and hitting saplings with both tires at the same time to fire roads they have water tankers driving down
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your expirence in the sand was apples to oranges tho, busa to 80 hp cvt, i got to imagine a rx1 or something making 150-180 hp would much be better suited to compare with a busa...
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Yup your right there...Mostly ::)...With the CDI going out on that trip it was a truley unfair comparison I went from just over 100hp. to prolly 35 to 40.
But I still think a bike motor in the sand is the way to go...Thats why there is a CBR 1000 sitting in my shop
Now for sand dragging I think that a bike motor with a CVT would be the clear shit just like you and I talked about...It would be easier on the clutch basket and you would have a shit load of gear choices, with the advantage that all of the spinning mass in the trans already in motion, and with the motor close to its peak torque before the buggy ever moves...
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I can't disagree with bug or spec on the last couple of posts.
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I have driven a quad with a group of Odysseys and Pilots on the sand. It seemed like I was shifting more than I was in any gear. Go up the dune down shifting as I lost speed then back down up shifting between one blip of the throttle.
The CVT parts for the lower HP stuff has more internal friction than the stuff for high HP. So it has to be tuned more specifically to the terrain. A theoretically perfect system with no internal friction would have one perfect tune and adjust to the terrain. A Cat roller driven and a 102C, 108C or any current sled clutch drive is pretty close. A steel ramp and rollers in the driven will put it even closer.
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I think we are seeing a trend.Smaller stuff respond well to a cvt while for real HP and a nice broad tq.curve a manual COULD be preferrable. The only point I am trying to make is that we shouldn't make sweeping generalizations about anything without knowing the specifics of the application AND what the driver desires.
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I think we are seeing a trend.Smaller stuff respond well to a cvt while for real HP and a nice broad tq.curve a manual COULD be preferrable. The only point I am trying to make is that we shouldn't make sweeping generalizations about anything without knowing the specifics of the application AND what the driver desires.
It all boils down to opinion anyhow, so there is no right or wrong answer regardless... ;D
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bingo.We have a winner.
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And I don't bring a knife to a gunfight ;D
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Unless the gun owner does not expect you to fight!! LOL!
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:r
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mfabber, what would kind of power do you mean when you say "big power, broad powerband"? I.M.O. there is no downfall to running "big power" in front of a c.v.t., thousands of turbo yammy sleds run250-350+ horsepower with basically no mods done to the clutch, (other than a lot more weight swinging) on the factory belt which was designed to harness 150 h.p.
Again it is a matter of opinion as to whether you prefer to shift or not, but I would guess that most people who have experienced well set up cvt clutches on several different motors with varying h.p. would have a hard time convincing themselves that the manual shifter is the way to go.
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It's all a matter of personal preference .Period. A cvt WILL enable a small motor to act as if it is larger. IMO that's the only advantage to a CVT beyond that it is just personal preference. IMO. If you like hearing an engine running at full throttle much of the time you will like them. If you like the increased fuel consumption you will also like a CVT. If you like precise throttle control you will not. If you like to be able to really feel and use the varying torque from the engine at different rpm's you will not like a CVT. As I said,personal preference will dictate what a person uses. There is no right or wrong answer.
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I'll take shifting every time ;D The drone of CVT tends to grate on me, just my preference!
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FINALLY ! Someone that agrees with me. I was beginning to think I was the only one!
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The driven clutch is torque sensing. When there is low load, the driven clutch will not restrict upshifting like it does under a high load. So the system will upshift and lower the RPMS. In Olav Aaen's clutch tuning handbook, which is often referred to as the bible of CVT tuning, there is a rule of thumb proved with a mathematical formula. More spring load and more cam arm weight that are still matched to each other will make the clutch operate more efficiently. The springs in a typical clutch have very little pre-load. The cam arms at low speeds primarily are pressing on the pivot pins and not the rollers that cause it to shift. Therefore, a typical CVT is at it's worst efficiency at low speeds. This is where high engagement speeds are common for fast take off. I use Heel Clicker clutch kits which come with very long springs and have a portion of the weight on the outside of the roller. The center of mass of the cam arm is now farther out from the pivot at engagement/low speeds. So the kit increases effective cam arm force and spring load at low speeds improving the efficiency of the clutch during engagement and at low speeds. On two machines, my engagement is lowered over 1000 RPMs. One gained 3 lengths in a 300 foot drag race and the other gained 2 lengths over their previous setups even though the engagement is so much lower. I can also now putt around at low speeds and lower RPMs than before. When I nail the throttle it does not bog like it would with standard arms and calibrated with a low engagement. The lower the power curve is, the bigger the difference it will make. The most significant gain I have gotten was on a 3 cylinder Geo powered buggy. I did not measure it, but would guess it picked up at least 5 lengths in a 300 foot drag. On an Ecotech, I would run a Comet 4-Pro with 4 arms instead of 3 and use Heel Clickers on that.