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View Poll Results: What transmission type do you think is best for getting more MPGs?
Automatic 0 0%
CVT 9 31.03%
Manual 20 68.97%
Voters: 29. You may not vote on this poll

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Old 05-01-2009, 02:10 AM   #1 (permalink)
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CVT vs. Manual vs. Automatic?

I was curious as to what people's opinions were on this. Personally I feel manuals are better for fuel economy. Automatics have a torque converter, which robs horsepower, and the shifts are not always timed in a fuel efficient way, because you can't really "short shift" an automatic except for lifting off the accelerator or using a Tiptronic shifter. However, shifting gears to lower your RPMs in an automatic takes power as well since they are computer controlled and jerky.

CVT's are great for their ability to remain within the engine's optimal rpm range, but they too require power to constantly change their gearing ratio. Manuals seem like the most logical to me, and returning to neutral and coasting is much more natural with a stick shifter than it is with an automatic drivetrain.

Sure, automatics and CVTs can go into neutral, but if my hand isn't always on the shifter, I'm not going to remember to put it in neutral at every hill or coast in neutral to every stop. In a manual on the other hand, this is natural for me. Also, automatics make an unpleasant jerk every time you switch from neutral to drive, especially during power transfer. With practice and a well maintained clutch, the transition from neutral to in gear is much much smoother in manuals.

The EPA might say that some autos and CVTs are surpassing manuals in city economy, but I believe this is due to their testing methods. With an auto at a stoplight, the RPMs are either at or slightly above idle and if you were to let off on the brake, the car would move forward without even touching the gas. This is wasted energy, forcing your brake pads to not only hold back the weight of the car, but the engine's low end torque/horsepower as well. Again, a manual wins for practicality when it comes to remaining in neutral at a stoplight, since you have to anyways, while most automatics and CVTs remain in first gear for when you lift off the brake.

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Old 05-01-2009, 02:19 AM   #2 (permalink)
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Would a manual CVT be the best of both worlds?
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Old 05-01-2009, 02:35 AM   #3 (permalink)
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Haha, I never really thought of that, but I guess if you had maybe a sliding shifter that you slid all the way forward for a higher gear ratio and slid backward for a lower gear ratio, that would be feasible. The only problem would be that you could easily lug the engine if you didn't lower the gear ratio appropriately.
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Old 05-02-2009, 10:42 AM   #4 (permalink)
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EPA's testing methods are also being worked by people who want the tests to come out in a certain way. Manuals are 10 points less drag resistance yet they get the same, and somedays less in EPA "testing". Maybe it has something todo with the 0-60 numbers eh?

The only downside I can find to the CVT is slow acceleration and possible durability issues. You still need to tune your engine for optimum results but at least you get to keep it in the sweet spot for accelerating and FE.
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Old 05-02-2009, 11:19 AM   #5 (permalink)
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The main reason that I've seen that manuals tend to get lower EPA MPG numbers for some cars is the poor gear ratios that they give them, because of the idea that people who want a manual transmission want a "sporty" car and with an automatic you can have it kick down if you step on the accelerator, but it looks like they are giving automatics some better gearing for crusing speeds, so even tho a manual transmission has fewer losses in it it's all in how it's built and designed.
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Old 05-02-2009, 12:09 PM   #6 (permalink)
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You may get a better indicator by looking at how vehicles designed for efficiency perform with automatics vs manuals. I.e. metros, civics, etc:

1998 metro 1.3 litre mpg ratings per fueleconomy.gov:
manual 33 city, 39 hiway
auto 26 city, 31 hiway

2004 jetta tdi:
manual 32city, 42hiway
auto 28city, 39hiway
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Last edited by dcb; 05-02-2009 at 12:21 PM..
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Old 05-02-2009, 12:41 PM   #7 (permalink)
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I've always equated manuals with better mpg. The "sportier" they are driven, probably the closer to an automatic the mpg would be.

While I would love to have a manual, the cost to swap one in would sure buy a bunch of fuel for the automatic.
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Old 05-02-2009, 01:18 PM   #8 (permalink)
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I won't buy a car, no matter how good, unless it has a manual shift, manual clutch transmission. My heart sank when I heard the 2010 Insight would only be available with a CVT. Driving a stick keeps me thinking about what's going on under the hood, and that mindset keeps me focused on efficient driving.

Even so, I voted CVT in the poll. No, I can't name a car that gets better mileage with a CVT than with a manual, but it *ought* to be possible to build a CVT to accomplish this. The CVT would just have to be tuned for maximum FE, that's all.

The 1993 Subaru Justy gets 28/33 with the 5sp, 28/32 with the CVT. Surely lower resistance CVTs have been made since then.

Interestingly, 2009 Toyotas with the 5AT do just as well as with the 5MT, and 2009 Hondas with the automatic actually deliver +1mpg vs the manual. Of course, the $1000 premium you pay for a 5AT would buy a lot of fuel.
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Old 05-02-2009, 01:37 PM   #9 (permalink)
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Quote:
Originally Posted by LUVMY02CREW View Post
...While I would love to have a manual, the cost to swap one in would sure buy a bunch of fuel for the automatic.
just for one datapoint, I swapped an s-series saturn to manual for $400 (from a parts car, w/new tires on it ) and using a looong weekend. The fact you can bump start it with a hand push makes EOC and pulse and glide much less nervewracking (will the starter work this time?). I actually had to push it and and jump in the other day, hence the starter rebuild thread

A stick enables more advanced "hypermiling" techniques as well as a notable degree of reliability (dead battery? use the 9 volt in your garage door opener to jump start the alternator field, then bump start the car), plus the inherent efficiencies of no slippage or friction scrubbing or extra weight/complexity/cost.

So getting over 40mpg is easy now, was getting mid 20s with the auto. The swap in my case has paid for itself many many times over.
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Last edited by dcb; 05-02-2009 at 01:43 PM..
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Old 05-03-2009, 06:26 PM   #10 (permalink)
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I voted "manual" because it opens up a wider range of driving techniques that will help save fuel. That's even before you consider any extra driveline loss from the transmission.

Speaking of which: The CVTs that I remember from when they just started showing up in mass-produced cars all had significant friction losses through the transmission. They were noticeably greater than those through a manual transmission, though I do not recall any numbers. Are they still like that, or have they figured out how to reduce the friction?

-soD

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