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Old 07-04-2014, 11:20 PM   #1 (permalink)
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CVT vs. 6 speed automatic

Been buying and driving some from of truck for the last 40 years. Last car I drove was a 93 Ford Tarus on an irregular basis. All the new car technology is almost mind boggling and in the interest of economy, I am curious as to what type of transmission will give better mileage results when comparing the CVT to a 6 speed automatic.

I may be in the market for the first car since a 1971 Camaro. Most of the literature on new cars talks about all the nice new features and little or nothing about what has been done to help it achieve better mileage. I am sure I can kick up the mileage on a new car, but would like to make a good decision to start with based on all of the choices in new car land.

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Old 07-04-2014, 11:27 PM   #2 (permalink)
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My uncles roommate has a 6 speed auto in his F150 and only gets 15.9mpg. I know this isn't much help at all, just thought I might say it anyway.
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Old 07-05-2014, 02:02 AM   #3 (permalink)
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I'm no expert, but I'd say a CVT will probably be better in most situations. They are made specifically to be idiot-proof and to be more efficient by keeping the engine close to its sweet spot as much as possible. If your engine gets its best efficiency at 2500 rpm, and you're able to keep it near that spot no matter how fast you're going, that's going to do a lot better than fluctuating above and below that spot as your gears change and your engine revs fluctuate. CVTs can be a bit unsettling to drivers not used to them though as they tend to really rev the engine high when you're accelerating. This is especially apparent on the cars with tiny engines.
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Old 07-05-2014, 02:09 AM   #4 (permalink)
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That's a kinda controversial matter. CVTs are praised for their flexibility regarding a match between the engine RPM and the "gear" ratio under load and terrain conditions, but their durability is sometimes objected. On a sidenote, Mercedes-Benz have replaced the CVT of the 1st-gen B-Class with a 7-speed dual-clutch AMT for the 2nd-gen.
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Old 07-05-2014, 03:03 AM   #5 (permalink)
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If the auto has a manual shift feature that you're willing to actually use, you could get better gas mileage with it because although you'd lose some engine efficiency compared to the CVT, the transmission is more efficient by a large chunk.

Some autos (lots of dual clutches do this or have some way to disengage) will coast if you tell it to upshift when it can't actually upshift again, and that makes pulse and glide really easy.
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Old 07-05-2014, 10:50 AM   #6 (permalink)
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There are generally two types of six speed automatics: ones with torque convertors and ones with dual clutches, aka "manuamatics". Efficiency wise, the latter is more efficient because it is basically a manual transmission that shifts and clutches itself. Ford's small cars and a few VWs use manumatics (or DSG, as VW calls theirs). Toyotas still use torque converters. Usually the only way to tell what a car has is by driving it because sales literature isn't exactly aimed at the technically savvy.

Economy wise, CVTs are somewhere in the middle. The of their advantages is a much higher top ratio for highway driving. As an example, my brother in law's Mitsubishi Lancer 2.0L CVT is at 2000 rpm at 75 MPH, which is incredibly high gearing for such a small engine. A CVT has the advantage of being able to quickly and seamlessly downshift as soon as you want to accelerate from that speed.

In summary, the six speed autos and CVTs each have their strengths. I do my research solely based on fueleconomy.gov and would not hesitate to buy either type of transmission, as long as the EPA fuel economy numbers are good.
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Old 07-05-2014, 11:17 AM   #7 (permalink)
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I've owned both and went from CVT to 6AMT in both my Fiesta and the wifes Kia Sorento. 6 speed dual clutch AMT is better, at least in current configurations. They have added another gear range to the Nissan CVTs after the ones I owned but my Fiesta at 46 MPG (rated 38 highway) isnot going anywhere soon unless someone makes me an offer I can't refuse.

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Old 07-05-2014, 01:03 PM   #8 (permalink)
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It's a very complicated question.

You have traditional automatics, with six / seven / eight speeds... and you have CVTs... and you have automated dual clutch boxes like the Fiesta's.

Then you break down the CVTs into CVTs with dry clutch packs or starter clutches and CVTs with traditional torque converters... and dual clutch boxes with dry clutches and those with "wet" clutches.

Best for economy I've ever seen is Honda's CVT with the dry starter clutch... but that one's infamous for breaking down and leaving you to buy a new surplus box.

Honda's newer CVT uses a torque converter. This grants you nearly the same economy when moving, but is less efficient in traffic.

dual clutch boxes, from what I've seen, come closest to manuals in traffic... the Fiesta's is good, but the ones we get here have a 6th gear that's way too short for my taste. The new Honda Fit CVT, on the other hand, has a lower "7th gear", and in full auto mode, runs 500 rpm lower than even that at a cruise.

And that's one thing to look out for if you do a lot of highway miles. However fancy your gearbox, if your top overdrive ratio sucks... it sucks.
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Old 07-05-2014, 06:46 PM   #9 (permalink)
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I think dual clutches are overhyped, standard autos are only barely slower and torque converters are more efficient than a slipping clutch from a start. Nowadays torque converter autos are mostly locked and so you don't lose fuel economy. DCTs with wet clutches have a "crawl" mode in 1st gear so they waste fuel around town too, just slightly less.
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Old 07-05-2014, 09:29 PM   #10 (permalink)
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Quote:
Originally Posted by serialk11r View Post
Nowadays torque converter autos are mostly locked and so you don't lose fuel economy.
Very true. I recently drove a 2011 Jetta 2.5L 6-speed auto, a classic torque converter auto with this engine, and I was astonished at how "positive" it felt when accelerating slowly in town. What I mean is that it kept upshifting to keep the revs between 1200-1500 and the TC was mostly locked once I was moving. It was the same as the brand new four banger Camry that I recently rented.

See...even the manufacturers can catch on once the CAFE laws are looming....

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