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Old 03-12-2011, 04:25 AM   #161
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Re: list of gas saving tips from best to worst

Can you elaborate?

Direct drive and its efficiency come from locking the input and output shaft together with a clutch rather than with gears. One is hollow at the end and the other rides inside it. When you shift into your direct drive gear, they lock together and no gears are engaged.

In a transaxle the output shaft (6) is in the countershaft's position, as shown in the cutaway, and can't lock to the input shaft (3) without gears (or, I suppose, a belt).
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Old 03-12-2011, 05:21 AM   #162
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Re: list of gas saving tips from best to worst

Wish I was fast at photoediting... I was looking for a schematic of the dual final drive transaxles but haven't found one... why not go direct to the tall final drive only?

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Direct drive and its efficiency come from locking the input and output shaft together with a clutch rather than with gears.
Don't know why that would be... just use dogs to lock 'em like the rest of the trans.
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Old 03-12-2011, 09:35 AM   #163
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Re: list of gas saving tips from best to worst

I see, you mean to skip the counter shaft and go directly to the differential's gear. I suppose that's possible. For that matter, how are those dual final gears packaged? Would it be possible to eliminate the counter shaft and go directly to 4, 5, or 6 finals?

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Don't know why that would be... just use dogs to lock 'em like the rest of the trans.
The central theme was that it doesn't go through a gear set, not what type of connection is in use. You are correct, it's dog teeth, not a smooth clutch.
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Old 01-03-2012, 11:48 AM   #164
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Re: list of gas saving tips from best to worst

Some of my farvorite driving style tips:
1. Limit speed to as low as you can bear given highest gear can be used.
2. Use engine breaking with high enough rev. for the engine to cutoff the fuel for as long durations as possible. On manual change directly to the gear you are going to use throughout the whole intersection and accellerating with after.
3. When you need to press the throttle down i.e. accellerate press it a bit more as long as you can use the extra propulsion without having to waste it on the breaks later on and the transmission doesn't downshift. (and speed or rev. doesn't get too high) This will keep the pump-losses down which are higher the more the throttle is closed on gas-engines.
4. If timing is not an issue (simple turn or roundabout without any coinciding traffic) wait until the last second and use the brakes as short as possible (if at all) pressing the pedal quite firmly. This will help save the breaks as well but may annoy passengers. It will help you continuously to let of the gas earlier.
5. If timing is an issue (traffic lights or cars ahead), sometimes breaking early can maximize the minimum speed you are going to have through a situation and avoid unnessesary stops. It helps if you are a good dancer not usually stepping on other peoples toes feeling the flow of the traffic.
6. Keep your distance to vehicles in front of you to avoid unnessesary braking and uneven speed.
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Old 01-03-2012, 09:38 PM   #165
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Re: list of gas saving tips from best to worst

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Originally Posted by theholycow View Post
I see, you mean to skip the counter shaft and go directly to the differential's gear. I suppose that's possible. For that matter, how are those dual final gears packaged? Would it be possible to eliminate the counter shaft and go directly to 4, 5, or 6 finals?



The central theme was that it doesn't go through a gear set, not what type of connection is in use. You are correct, it's dog teeth, not a smooth clutch.
The problem is, a 2 speed rear axle just has a planetary gearset inside of the ring gear. Basically, it's functionally the same as a 2 speed automatic transmission. Just with it having no reverse there is only one clutch to operate, which is easy to do with either a servo or vacuum. Once you go more gears than that, you need to start getting a more complex control system, usually to be handled by a hydraulic system.

Once you do that? Well, you've got a full fledged automatic transmission there, with all of its faults and inefficiency.

I don't see why you keep perceiving the direct drive gear to be any more efficient than a gear that routes power through the counter shaft in a manual trans. The only reason I can think of is that perhaps it might seem like the parasitic losses of spinning up all the other gears would pull the trans efficiency down. But the problem with that is that modern transmissions are constant mesh. Every gear is constantly spinning with every other gear at all times, so the parasitic loss is there even when you're hooked up to direct drive. It's just which gear is connected to the output shaft.

Having the dog gear link the input shaft to the output is functionally no different than having the dog gear link the counter shaft to the output through any of the other gears. A solid, non-clutched, non-movable gear is welded to the input shaft which is meshed to a solid, non-clutched, non-movable gear welded to the counter shaft.

I think you're reaching for gains which don't exist.


But even if there were miniscule gains to be had... They would be more than eliminated by slapping an automatic transaxle on the rear end.
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Old 01-03-2012, 10:06 PM   #166
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Re: list of gas saving tips from best to worst

I've been talking about fwd, and FWD Tempos don't have planetary gears in their rear axles.

I'm not quite sure of the Tempo's exact layout tho' for that funky 2speed final drive. But if for top gear all the other meshes and whatnot could be bypassed, how could there not be a couple percent efficiency gain?
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Old 01-04-2012, 05:55 AM   #167
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Re: list of gas saving tips from best to worst

Interesting necrothread. Good point about everything being constant mesh, but I have the feeling (with no research to back it up) that unloaded gears in constant mesh represent much less waste than a single pair of meshed gears under load.

The 2 speed final drive I was talking about is in some FWD transaxles, such as VW's 6 speed manual.

With regards to RWD I was talking about how there is a 1:1 ratio (4th in mine) that transmits power through one less set of meshed gears, and how that is purportedly the gear where the least drivetrain loss happens.
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Old 01-04-2012, 03:46 PM   #168
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Re: list of gas saving tips from best to worst

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Originally Posted by theholycow View Post
Interesting necrothread. Good point about everything being constant mesh, but I have the feeling (with no research to back it up) that unloaded gears in constant mesh represent much less waste than a single pair of meshed gears under load.

The 2 speed final drive I was talking about is in some FWD transaxles, such as VW's 6 speed manual.

With regards to RWD I was talking about how there is a 1:1 ratio (4th in mine) that transmits power through one less set of meshed gears, and how that is purportedly the gear where the least drivetrain loss happens.
Even with the 2 speed final drive being on a front tansaxle, the principal is the same. It has a simple single planetary gearset with a single clutch operated by a single servo. To gain more speeds, you'd need additional gearsets, which would amount to an automatic transmission and all losses involved thereof.

I still do not see how the 1:1 would be effectively more efficient, as there are all the same gears in mesh causing parasitic losses due to friction and oil viscosity. Both the direct drive and any gears all use a single dog gear to link them to the output shaft. All of the gears have the power transfer through a single dog gear. I just don't see how there could be any loss of efficiency worth noting.

My statement still strongly stands that attempting to focus upon the 1:1 gear by attempting to get additional speeds out of the final drive would be a net loss. The miniscule gains that may or may not be gotten from eliminating the counter shaft will be very much erased by the complex control system required to make use of a multiple speed final drive set.
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Old 03-26-2012, 10:17 AM   #169
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Re: list of gas saving tips from best to worst

some suggestion in the link

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Originally Posted by bzipitidoo View Post
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So far, I have gathered that this is what you should do to save gas, in order from the quickest, easiest, and cheapest ideas, to the more expensive, inconvenient, uncomfortable, dubious, and/or difficult ones.

1. inflate tires (to at least the maximum recommended on the tire walls)
2. throw out extra weight: clean out the beer (root beer of course, officer) cans and bottles, etc
3. change your driving habits: drive slower, accelerate more slowly, try to do acceleration on downhill slopes and avoid accelerating on uphill, coast up to stop lights, shut engine off when stopped.
4. change to lighter weight oil
5. install a gas mileage indicator (to help with #3)
6. Maintenance: Keep engine tuned. pay special attention to the O2 sensors

Those are the easiest and best. From here on it gets worse with respect to sacrifices, significant expenses, dubious benefits, or decreased safety.

7. Limit power use: no A/C, no loud radio, drive in daytime so won't have to use headlights. change incandescent bulbs to LEDs.
8. upgrade to low rolling resistance tires.
9. More radical changes in driving technique: Shut engine off while coasting (not always legal, is that?) and master technique of restarting engine with clutch rather than starter, make high G turns rather than touch those brakes,
10. more serious weight reduction: dump the spare tire and jack and carry a cell phone and an emergency number instead, trade out steel rims for lightweight aluminum, replace steel hood and fenders with carbon fiber (if available for your vehicle), maybe trade out glass side and rear windows for some sort of plastic, toss out the passenger and back seats
11. trade up to a more efficient car (if what you have is nothing special)
12. aftermarket engine upgrades: headers instead of stock exhaust manifold, camshafts specially tuned for FE . Hotter thermostat, electric fan for radiator (well, most cars do that nowadays), chips.
13. do it yourself aerodynamics: make skirts for the wheel wells, spoilers, build up back so it's more like a teardrop shape, do something about the side mirrors, and do what you can to smooth the underside.
14. add solar cells to lighten the load on the alternator.
15. Or dump the alternator and change to a deep cycle battery, and get a charger. recharge often.

And now, to boldly go where no one has gone before. Or very few have gone, because it's so uncertain and heart stoppingly expensive.

16. Radical body: Acquire a body made entirely from lightweight material, be that aluminum, magnesium, or other alloys, or composites. How one keeps it street legal, I don't know.
17. Radical engine work: make something that can burn methanol, and dispense with the radiator and water pump (Scientific American article from some 10 years ago), go with a dry sump (Hey Smokey column in Motor Trend from years ago), and where oh where is the 42V standard will all the cool gas saving features like electrically actuated valves with whatever timing was desired and no losses from camshafts, a single winding for both alternator and starter integrated with the flywheel and the wonderful ability to instantly start, etc. Still all ICE tho.


No doubt I missed plenty of ideas. And please discuss the ordering. I'd like to see something like the above list somewhere, perhaps as a FAQ. Or is there already such a list?
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Old 03-26-2012, 06:09 PM   #170
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Re: list of gas saving tips from best to worst

Great list. I know you listed vehicle maintanence but I would include change air filter more specifically. Or an ugrade to a high performance filter would be even better. Gotta let that car breathe!
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