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MPG as related to transmission

Discussion in 'Technical Chat' started by BurqueTaco, Aug 12, 2012.

  1. Aug 12, 2012 at 12:55 AM
    #1
    BurqueTaco

    BurqueTaco [OP] Well-Known Member

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    Albuquerque New Mexico
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    04 trd tacoma 4x4
    Custom pinstriping, pleasure hole, Fox 2.0 rear, Fox 2.0 coilovers.
    For many years, long before i started driving, I was under the impression that having a manual transmission will almost always increase you're gas mileage (excluding the fancy new computer BS trannys). In my experience this has always been true. My current vehicle is a 2004 tacoma trd with 50,000 miles and a manual transmission that averages 20-22 mpg in town and 23-24 at optimal speed. I'm wondering if other people have had this experience or if they think I am full of shit (this is the response i get when i post my mpg in mpg threads).
     
  2. Aug 12, 2012 at 11:37 AM
    #2
    tan4x4

    tan4x4 Well-Known Member

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    Rick
    Folsom, CA
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    Thats pretty good gas mileage for a 3.4.
    I get about the same with my 2.7 and automatic.
     
  3. Aug 12, 2012 at 12:03 PM
    #3
    Adam Baum

    Adam Baum Well-Known Member

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    I've got an automatic 3.4L V6....averaging 17.5 MPG combined. On long highway trips I'll get 20MPG. This is a decrease of -2MPG because I went with a taller tire (it was on sale).

    thinking about swapping in a manual transmission, but I'm not sure if the +2MPG it is worth the cost.
     
  4. Aug 12, 2012 at 12:08 PM
    #4
    Rich91710

    Rich91710 Well-Known Member

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    Los Angeles
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    Satoshi with FJ badge, factory cruise, factory intermittent wipers, Redline Tuning hood-lift struts, Hellwig Swaybar, Rosen DVD-Nav
    The key is optimal speeds.
    OP is in New Mexico. My worst MPG was in New Mexico and Texas with the 80mph speed limit.

    If I really cared to maximize every tank, I could pull solid 26-26.5 out of mine. That's a 45 mile traffic-free commute in the morning, and the reverse stop and go coming home.
    There have been mornings that I've left 10 minutes early and held my speed down to 60-65 on the way in and managed to pull a solid 27.5 for the commute.

    But I don't care to maintain THAT level of "stinginess" on my fuel usage... considering that I went into the Taco from a 12mpg Suburban that I spent $150 a week on fuel.

    My results are logged in my Fuelly account linked in my signature graphic.

    2008 RC Base 2wd 5-Lug, 2.7, 4spd Auto.


    40 years ago, manual transmissions were always better than automatics. The main thing was the loss in the torque convertor. As manufacturers started adding overdrives, and lockup torque convertors, the relative efficiency of automatics has caught up to manuals, so these days, there's not a huge difference, and in most cases, the average driver tends to do a bit better with an automatic because they will either short-shift and lug the engine, or hold a gear too long and over-rev, wasting fuel.

    An experienced driver, well "in tune" with his engine, can pull better economy from a manual.
     
  5. Aug 12, 2012 at 4:39 PM
    #5
    lhedrick

    lhedrick Active Member

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    Larry
    Utah
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    It's clear there is a lot of bad science on this MPG/transmission subject.

    At the core manual transmissions have 2 shafts. One connected to the engine via the Clutch. The second connected to the wheels. 2 shafts, main shaft -- lay shaft. All the gears are connected at all times with the gears on the output shaft and they are just spinning when in neutral. They get locked to the shaft as we shift.

    At the core of an automatic is a collection of gears connected in a planetary arrangement. This is difficult to describe so I would refer all to look up "planetary gears" on wikipedia.

    What makes the automatic possible is the automatic clutch known as the torque converter. Modern ones are much more efficient then those of the past. The 6 speed auto in the toyota locks up in 4, 5 and 6 but, it is not always locked so it can never be as efficient as a manual transmission. The reason a towing package is only offered on automatics is because a manual has no need for one. When pulling a big load up a steep hill the torque converters will unlock to develop more power. This causes the oil inside them to heat up and requires and additional cooler to keep the oil from getting too hot. To do all this the new 6 speed automatic/torque converter/cooling option is big, it's heavy and it adds a few thousand to the cost of the system. I have my doubts they will run 250,000 miles like a simple 5 speed manual and a rebuild is not going to be cheap.

    Next, gas milage is determined by fuel burn and that is determined by air pressure in the intake manifold. Open the throttle, air pressure goes up and the fuel injectors can open longer for more burn and more power. The transmission does not come into play in any way. Now if you run at 60 in 2nd gear at 6000 RPM on either there will be higher loses as pistons need to stop and change direction 6000 time a minute.

    If Toyota, the EPA say one gets better millage then the other they have flawed data. If the gear rations are the same the manual will always do better if a driver does not over rev the engine. The gear rations on the Toyotas are not the same on the 6 speed automatic and manual models. So any comparison is not valid.

    If you are crawling over rocks at 1 mph the torque converter will unlock and multiply power just like riding a clutch. The automatic will be much easier to handle then doing clutch work. So, the toyota has lower gears on the manual for very low speed but that trades off a bit of MPG at the high end as the RPM will be higher on the highway with the manual. Think about it, you need to climb over a rock ledge. You bring the wheels up to ledge and slowly add power. The RPM starts going up but we are still not moving. The circulating oil starts to build power before we start moving. Where does that power go if we aren't moving. It goes into heating up the oil.

    Remember when a manual transmission is in gear, it is locked to the back wheels and power transmission is virtually 100 percent. Step on the gas and it is still locked. On an automatic most torque converts will unlock when you step on the gas. You can watch this on the tach and see as much as a 200-300 rpm increase when you step on the gas. This is due to the converter unlocking causing fluid to circulate generating wasted heat and fuel.

    Automatics are fine for those who want them but,they are not more efficient. When a sales person tries to dump this stuff on people they need to ask why or say prove it. People need to know what they are buying before they go into the dealer. They should be able to tell the dealer when he is full of BS.


    The following do not use automatic transmissions
    motorcycles
    race cars
    10 wheel dump trucks
    big rigs
    trains

    All freight hauling trains are driven by electric motors which get the power form giant diesels which run 1 speed all the time and turn electric generators.

    There is a reason why there are no automatic transmissions on the race track. How big would the 6 speed transmission on my 250 dirt bike be if it was replace with a 6 speed automatic and torque converter? Worst of all how much more would it cost?

    All this automatic stuff is adding thousands to the cost of our transportation.
     

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