From what I heard, when you step on the gas with a car with CVT, the RPM is suppose to rise up for maximum acceleration. When cruising the engine speed is suppose to drop itself for maxima fuel efficiency right? But mostly when cruising between 40-65mph it stays around 2,000-2,500 rpms. But my conventional transmission (as they call it now) when at 40mph is around 1,500rpms, and when I'm about 60mph the engine speed is around 2,000rpm. So correct me if I'm wrong the slower the engine is turning the transmission the more fuel efficient the car right? for example if I'm cruising in my '02 maxima A/T at 50 mph, while also driving along side a '07 maxima doing 50mph as well, while my A/T is revving the engine at 1,700rpm the CVT is revving at 2,000rpm. Which one is more fuel efficient?

 

The cvt is electronically controlled always adjusting for best torque and fuel economy. I asked earlier about a torque conveter and was kinda shot down. Nobody had a real answer. I contacted level 10 and another place and they said they could do something but most people here said they werre full of doo doo.

 

From the net!!!


CVT” stands for continuously variable transmission. What that means is that they are “infinitely variable” or without discrete steps – or “stepped gears” – like a traditional automatic transmission.

The continuously variable transmission offers many times more gear ratios than any automatic “step” transmission.

It does this by doing away with gears entirely. Instead, CVTs work with a heavy-duty chain belt. The reinforced belt runs between two cone-shaped pulleys. One pulley is hooked to the engine and the other is hooked to the drive train. As the engine turns the pulley hooked to it, the belt transfers power to the other pulley that is hooked to the drive shaft, which powers the wheels.

The portion of the pulleys that the metal belt runs over varies in diameter according to driver demands and other conditions. Varying the diameters of the pulleys is similar to the changing of gear ratios in a standard transmission, but it happens in a continuous flow, instead of in discrete steps.

The obvious benefit is smoothness because there's no shifting. But CVTs are more efficient, too, and thus save about 4 percent to 8 percent in fuel versus the traditional four-five speed automatic. The second-generation CVT used in these vehicles relies on electronics to determine the ideal ratios based on driver intent and current operating conditions, including engine speed and load. Because changes take place smoothly, shift quality – the “feel” of the transmission changing gear ratios – is excellent.

 

Thank you for explaining how it works, but is it only more efficient when i guess driving in city? Because the test i'm talking about is during highway cruising speeds. Or is it because the way its setup it doesnt matter if the cvt has higher rpms at a set speed that it will be more efficient then a regular transmission traveling at the same speed at lower rpms?

 

Linkage: http://auto.howstuffworks.com/cvt.htm

 

Do you feel sluggish at 2k RPM on the highway and having difficult time keeping constant speed? If you have dificulty keeping constant speed, then it's less efficient regardless of the RPM. I drove an Impala recently, as a rental; when it went in the 1/2 cylinders mode (from 6-3), it had a very difficult time keeping the speed at 70 on the highway and kept kicking back to all cylinders mode, and ended up with about 24MPG highway.

I think my 5AT could use a 6th gear to lower the RPM another few hundred revs for better MPG when cruising around 70 MPH.

 

Hey thanks i guess it answers my question, but i'm not talking about stop and go i'm talking about on the highway cruising at a certain speed with cvt and an automatic transmission

 

but thats the thing it doesnt feel sluggish. Maybe i'm asking the wrong question. so i guess it doesnt matter how high the rpms in a CVT revs when lets say going a constant speed of 50mph it will always be better than a auto transmission that may rev lower with the same constant speed of 50mph? With both cars cruise control set to 50mph which car would be more effiecent the one with CVT that revs at 2,100rpm or the auto trans that revs at 1,700rpms?

 

The one with lower RPM that can still putt along is probably more efficient. CVT still has maximum and minimum ratio.

 

I think efficiency is more than just rpms at specified speeds. Wheels, tire size and profile, gear ratio, vehicle weight, etc, etc could enter into the equation.

I look at highway MPGs, and from what I have been seeing here on the ORG, and in talking to the two '07 Maxima owners I know, the highway MPGs of the 5 speed '04 (mine as well as others here) and that of broken-in '07s with CVTs seem about the same (usually 26 to 30, depending on conditions). And the '07 is heavier than my '04, and heavier still than the '02s.

However efficient the CVT may be at this point, I am convinced it will be even more efficient in the future. Finding a way to reduce the heat buildup alone will make future CVTs clearly more efficient that the one in the '07 Maxima.

 

Thank you for answering my question lightonthehill!

 

Having owned five previous Maxes, and now owning an "07, I can unscientifically report the the mpg on the '07 is WORSE than any of the prior five! I have 9K miles on it so perhaps it isn't "broken in" yet.

 

This is my first car with CVT (and first Maxima). Prev on my accord, it'd really jolt you switching gears with the automatic. I really like this CVT system and the how stuff works article was pretty neat. Thanks for linking.

As far as gas mileage, I knew it'd be worse than my 4 cyl. accord, but its not as bad as my GF's v6 SUV. On the plus side, I finally let her drive my car and now she wants to steal it...

lol

 

jc53 - When considering mileage, do not overlook the fact the Maxima has gradually moved up from 2900 pounds (1981) to 3600 pounds (2007) over the years, has gotten ever more roomy, and has increased engine power many times. I owned two 1985 Maximas, and they had nowhere near the room or power my '04 has. Just moving up from my 2000 SE to my 2004 SL took the Maxima from 222 HP to 265 HP.

Also, in many parts of the country (such as where I live), traffic is three times as bad now as it was just twenty years ago.

Lots of factors involved here.

 

Gasoline Engines 101 says that maximum fuel economy occurs at the point of maximu torque -- which in the VQ engine in my 04 is supposed to occur at 4,400 RPMs. Well, I don't believe that is the case in the VQ engine. The torque curve for this engine is essentially flat from about 2,200 RPMs up to just above 4,400 RPMs. So I like to belive that the maximum fuel economy occurs closer to 2,200 RPMs, but most likely above 2 K RPMs.

You don't get maximum fuel economy when the engine is even slightly lugging. And I believe that at 50 MPH and 1,700 RPMs on a level road this engine is slightly lugging.

So to answer your question, I think you will get maximum gasoline mileage in top gear with the engine turning between 2.0 K and 2.3 K RPMs. But I have no tests to prove my theory -- only my experience driving my 04.

My 6-speed in top gear runs the VQ at 2 K RPMs at 55 MPH. At 3 K RPMs in top gear the speed increases to 82 MPH. My gasoline mileage drops the faster I drive above about 60 MPH or so.

I have disagreed with "light" in other posts on the ability of auto engineers to improve the heat generation "efficiency" of the CVT, so won't discuss that again, here.

"light" is certainly correct on the mileage I get with my 04 and 6-speed. Driving the interstates between 65 and 75 MPH, I average between 26 and 30 MPG -- with the 30 only seen when the wind is at my back.