Looking back at the WIlliams F1 car with a CVT, and combining that with the blown diffusers from F1 a decade ago, or hell.. the Brabham BT46 fan car from 1978..... always have the fan spinning max revs... man... that would be an amazing combo...
Looking back at the WIlliams F1 car with a CVT, and combining that with the blown diffusers from F1 a decade ago, or hell.. the Brabham BT46 fan car from 1978..... always have the fan spinning max revs... man... that would be an amazing combo...
We had a guy who used to autocross an Altima with a VQ35 and a CVT. One of our most experienced and skilled drivers took it out for a few runs and came away saying he was honestly impressed with that powertrain in an autocross car. He said basically anytime you needed power it was there.
A good article from elsewhere - Some other magazine
The highlight is, its better anywhere that the math works out that losses from being off of the peak of the powerband (non-cvt disadvantage) outweigh the frictional losses (CVT disadvantage), which would be most cases.
As far as seeing them around, here are the reasons.
If you think you wouldnt like how one drives, you would HATE driving a Tesla! EVs drive very similarly to a CVT. They are just quiet, so a happy middle ground on issue #1 above.
And because...
Rubber belt (CVT, SxS, etc) is a pull belt, the push belt in the above video is the more current tech.
NickD said:We had a guy who used to autocross an Altima with a VQ35 and a CVT. One of our most experienced and skilled drivers took it out for a few runs and came away saying he was honestly impressed with that powertrain in an autocross car. He said basically anytime you needed power it was there.
I was always interested in this idea. I drove a vq maxima with the CVT as a rental car about 5-6 years ago and other than the final drive being too tall*, I thought it was actually really well done. I would've loved to autox it. The stupid part was that you could put it in 'manual mode' and it would pretend it had 6 gears that you could shift through, lol.
*even full throttle from a stop the engine didn't get to redline until about 35-40mph, indicating to me that the trans was in 'lowest ratio' but the final drive was too tall. I bet they could take a full second off the 0-60 if they let the engine get going much sooner, as from 35-90 it was a monster. But fuel mileage and cruise RPM and top speed, wah wah wah.
In 2010ish the FSAE team I was on looked really, really hard at using the 580cc twin and CVT combo out of a Honda Silverwing scooter- the plan was to tune the engine for a very narrow powerband and use the CVT to keep it there. It was eventually abandoned not because of the CVT, if I'm remembering correctly it was because the poor scooter engine couldn't make enough power to justify its' own weight regardless of how much boost we crammed into it.
I drove a CVT Nissan rental car to visit the Mitty a decade or so ago. It was not a good example of the breed, between the DBW programming and the CVT programming it couldn't maintain a steady speed on the interstate. It would either not quite make enough power to maintain speed or it would jump up 500 rpm and accelerate. It's been a while, but I remember it feeling like there was some hysteresis built into the throttle so you couldn't make very fine adjustments - probably to prevent surging with small foot movements, ironically. That car made me realize that yes, there are still bad cars being produced.
But my parents had a 2018 (?) Legacy with a CVT and it was a really good implementation. It just felt like a slurring auto and managed to perform quite satisfactorily for what it was. It also had the fake "manual" mode that I never used because it just seemed ridiculous. It was the sort of CVT that nobody would ever actually notice. This is obviously easier in a car that doesn't have an overt engine presence.
I agree that a Tesla (or other EV) feels similar, but the lack of a droning ICE really changes the experience. Instead of engine noise doing something you don't expect, you just don't get engine noise. So it does have quite a different flavor to it.
Tom1200 said:I also run an F500; I road race and autocross mine.
My run starts at 2:26.
https://m.youtube.com/watch?v=j3J3g-I3kw0
The CVT works great for autocross; you never have issues being stuck between gears. Geared properly the car is always in the powerband.
The other great thing about a CVT is you can buy about $150 - $200 in parts will allow you infinite gearing changes. This is way more economical than coughing up 3-6K for a close ratio gearboxes. They also don't break unlike some of those fancy gearboxes.
Note while most of the F500 road race cars are.not motorcyle powered cars at last years RunOffs James Weida damn near won with a a CVT powered car.
I initially thought I would miss the gearbox for road racing but now having done a few races with the car I can honestly say I never even think about it once I'm on course.
How do they behave on closed throttle decel? Do you have engine braking? Or is the engine braking also variable? Wow, there's an interesting car setup option...
Woody (Forum Supportum) said:I would think that CVTs might work well in Land Speed racing....
...but I'm basing this on exactly Zero experience with either CVTs or in Land Speed racing.
For LSR cars, the goal with a transmission is usually minimal friction. You've got a lot of distance to make up for not quite being able to keep the gearing optimal the whole run.
Keith Tanner said:How do they behave on closed throttle decel? Do you have engine braking? Or is the engine braking also variable? Wow, there's an interesting car setup option...
On closed throttle there is a minor amount of deceleration; this more down to the drag in the CVT belt than the engine compression braking, of which two strokes have almost none. It is just enough that the car will rotate slightly off throttle but you mostly use the brake to rotate the car. Trail braking is your friend in these cars. Engine braking is not variable.
While there is something to be said for the sound of a car banging through the gears, honestly I'm not sure that most of the 'droning' people complain about with CVT's is as much a function of the transmission function itself as it is the engine it's attached to. Remember, they're generally running a 2-stroke and/or low cylinder count engines that naturally has a less ear pleasing sound even if attached to a conventional manual transmission. Consider that higher cylinder count racecars running flat out on a super-speedway have very little engine rpm change, and yet the fans seem to enjoy the sound for hours on end anyway with little more than a bit of Doppler effect. Same with the top levels of drag racing. Hell, even at the end of a long straight cars are increasing rpm rather slowly. Yet I've never heard anybody complain about the droning sound of an I6, V8, or V12 racecar there.
"Ugh... Did you hear that 250 GTO just DRONING its way down the Mulsanne Straight?" -Nobody Ever
Keith Tanner said:Tom1200 said:I also run an F500; I road race and autocross mine.
My run starts at 2:26.
https://m.youtube.com/watch?v=j3J3g-I3kw0
The CVT works great for autocross; you never have issues being stuck between gears. Geared properly the car is always in the powerband.
The other great thing about a CVT is you can buy about $150 - $200 in parts will allow you infinite gearing changes. This is way more economical than coughing up 3-6K for a close ratio gearboxes. They also don't break unlike some of those fancy gearboxes.
Note while most of the F500 road race cars are.not motorcyle powered cars at last years RunOffs James Weida damn near won with a a CVT powered car.
I initially thought I would miss the gearbox for road racing but now having done a few races with the car I can honestly say I never even think about it once I'm on course.
How do they behave on closed throttle decel? Do you have engine braking? Or is the engine braking also variable? Wow, there's an interesting car setup option...
Due to the way the ramps are in the clutches, it coasts.
In reply to Apexcarver :
I keep the belt side clearance as tight as possible, my car is a bear to push, and so there is a bit of drag. Read no freewheeling.
When the side clearance is out of spec the car in effect is starting out with taller gearing. The primary clutch has to squeeze the belt up higher the sheaths to engage, and so it's running on a larger circumference, it's like adding a one or two teeth to a countershaft sprocket in a bike. This is primarily an issue for Autocross, on a road course I tend to preload the throttle anyway so the primary clutch is semi engaged already.
In reply to Keith Tanner :
When implemented on snowmobiles the CVT does have the potential for engine braking, but it's not as simple as closing the throttle. You need to maintain enough throttle to keep the primary clutch engaged in order to get engine braking. I suspect on an F500 you could see some engine braking but it would depend on hearing and clutch tuning in addition to altering driving style and possibly using left foot braking while applying limited throttle to keep the primary clutch engaged.
Depending on the tuning of the primary clutch (ramp profile/springs/weights) you can alter the engagement rpm and also make it to where the movable sheave "snaps" in to grab the belt rather than gradually moving in to contact. The higher the engagement RPM and sharper the cutoff between engagement and disengagement will limit the ability to feather the throttle and get any noticeable engine braking.
The tuning of the driven pulley can help if it's set to back shift (cvt equivalent of downshift) aggressively when the applied torque drops off.
I have a 2018 Fit with the CVT. For reference, the engine for the CVT is derated 1 ft-lb and 1 HP vs. the manual. In regards to the "fake gears," they are just like the 321 under D in a regular automatic. If you need more engine braking for a downhill, you use the fake gears. If you want to keep the transmission from upshifting when you come off the gas coming into a corner, use the fake gears. Selecting a minimum RPM would be more useful, but fake gears is what they offer.
A CVT with fake gears is like a naturally aspirated engine with fake turbo lag.
If I wanted to run the engine at a sub optimal RPM, I'd just run a manual trans
No Time said:In reply to Keith Tanner :
When implemented on snowmobiles the CVT does have the potential for engine braking, but it's not as simple as closing the throttle. You need to maintain enough throttle to keep the primary clutch engaged in order to get engine braking. I suspect on an F500 you could see some engine braking but it would depend on hearing and clutch tuning in addition to altering driving style and possibly using left foot braking while applying limited throttle to keep the primary clutch engaged.
Depending on the tuning of the primary clutch (ramp profile/springs/weights) you can alter the engagement rpm and also make it to where the movable sheave "snaps" in to grab the belt rather than gradually moving in to contact. The higher the engagement RPM and sharper the cutoff between engagement and disengagement will limit the ability to feather the throttle and get any noticeable engine braking.
The tuning of the driven pulley can help if it's set to back shift (cvt equivalent of downshift) aggressively when the applied torque drops off.
I should say, effectively, it coasts. its certainly not like a conventional transmission on lifting the throttle. Yes, its a real B-word to push around a paddock, but at speed on course, you dont have that much decel.
As far as left foot braking, its mandatory on my F500 and I would suspect the vast majority of them due to footbox packaging. There is absolutely no reason to not left foot brake a CVT car. You do pre-load the throttle a bit, as you note, there is a bit of reaction delay to the CVT picking up the belt (engine RPM climbing to engagement point).
In reply to Apexcarver :
So my little driver brain thought at some point I would put a bike motor in (for road racing) but between autocross, where the CVT is the way to go and that on a road course I don't really notice the CVT centric things, it just doesn't seem to matter.
I will say it took me a few sessions on a road course to get in the groove as far as picking up the throttle; the difference in technique is fairly subtle.
Race starts are cool; I've been keeping it at 1/2 -3/4 throttle and holding it back on the brakes. Even if you don't do this the motor is well on the pipe so you don't lose out.
Speaking of automotive CVTs...
Is it true that they essentially have the same gearing in reverse as in drive (forward)? So you could get up to 60-70mph in Reverse no problem, if you wanted to, say, put a modern Subaru drivetrain in the back of an ACVW chassis...
In reply to Pete. (l33t FS) :
Would that be loading up the wrong side of the diff gears? Or small enough weight/power that you're not worried about it?
In reply to buzzboy :
The second one. Small weight, stock power, low duty cycle.
I grew up riding snowmobiles but got out of it about a decade ago when they started getting to be 200+ hp machines.
All I can tell you is until you have experience the 0-60 times of a well set up snowmobile with traction than most people haven't experienced acceleration. Yes a 1000 sport bike may be close but a well set up powerful snowmobile is a truly wild experience. My last machine was slow (140hp) but could probably do 0-60mph in 3-4 seconds depending on conditions) now trail sleds have 100more horsepower than that.
I think the ideal combo is low weight high hp, where the losses from the cvt are overcome by the ability to stay in peak power all the time and never having to loose power of suffer the driveline shocks of a shift.
In reply to 1SlowVW :
My F500 is 780lbs with me in it. The Rotax 494 engines are 100hp but I'm currently running the old AMW that the car came with, it's rated for 83hp. With autocross gearing it it has the ability to spin the tires in all but the fastest sections of a course. So yes power loss for the CVT isn't an issue.
A-mod autocross cars use 850cc snowmobile engines belting put near 200hp, power loss from the CVT is really not a problem with those.
In reply to 1SlowVW :
I rode a friends 750 Rocky Mtn King one winter.
Not a huge sled but big enough. I thought I was going to die in the wilderness.
I think that Baja SAE (a collegiate competition) uses CVTs, they all have the same 12HP Briggs & Stratton engine as well.
That's more about the rules of the competition than anything else, though.
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