Why drive a manual?


#121

The water flowed downhill from the mountains. I’m guessing that was due to GRAVITY. We have many highways that go downhill from the mountain pass summits in both directions. A human could build an unpowered vehicle from natural materials at the summit and harness gravities stored energy to travel in either direction. Solar, wind, water, fossil fuel, nuclear, muscular, and gravity have no useful energy for humans unless we harness it. Do you actually have a point?


#122

The point is that if gravity provides the energy needed to go from point a to point b, then in order to go from point b to point a, you have to give gravity that same exact amount of energy back. Gravity takes away energy as well as gives energy.
Otherwise, there would be no need for chairlifts at ski resorts, you could just build a downhill trail back to the top of the mountain.

When the moon gets closer to the earth, it speeds up, the loss of potential energy becomes a gain in kinetic energy. When the moon gets farther away, kinetic energy becomes potential energy and the moon slows down. The total energy, kinetic plus potential, is constant.


#123

All true. This is what confused me.
What lifted that water up into the lake behind the hydroelectric dam in the first place? Heat from the sun?
Of course heat from the sun evaporated water from the earth’s surface. The vapor rose to a high enough altitude for it to cool, condense, and become sufficiently heavy to be returned to the surface as precipitation by gravity. I learned that in elementary school. A very small amount would fall directly into the reservoir behind the dam. Much, much more would fall to the surface at altitudes higher than the river and reach the dam which restricts the water flow and fills the reservoir creating stored potential energy. With a sufficient level of water behind the dam the conduits located near the bottom of the dam are opened releasing some of the stored water. This water is pressurized by the weight of water above it and has sufficient energy to spin the generators thereby producing electricity. While the Pinewood Derby car itself generated zero emissions during it’s brief journey the O2 consuming CO2 producing organism that lifted it did. Same as an EV using electricity generated by coal, oil, or even natural gas. “Heat from the sun” as a question rather than statement for some reason derailed my thought process. All this electricity consumption and fingertip wear and tear over a fairly lame quip directed at Bing! Situation normal at CarTalk Community.


#124

I guess you lost me on the radiation of the sun and so on, but in South Dakota anyway, gravity seems to work pretty well in generating electricity. It’s a net gain, anyway.


#125

ummm… the sun’s thermonuclear (fusion) energy comes from gravity-mediated aggregation of hydrogen and the fusing of nuclei


#126

But it’s the fusion of hydrogen that is the source of the energy. No gravity is consumed in the reaction.

Is a desmodromic valve train more parasitic than a conventional valve train, after all, in a desmodromic valve train, the cam has to both open and then close the valves whereas in a conventional valve train, the cam only opens the valves and a spring provides the energy to close the valve meaning the the cam only has to do half as much work.
Do you recognize the flawed logic in this argument?
Is a spring a source of energy or only a means to temporarily store energy from another source?


#127

Ehh, that statement is not correct. On a conventional valvetrain it takes force (energy and resistance) to depress the valve spring, whereas on a desmodromic setup, there is no valve springs. That equals less internal resistance in the engine.

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#128

Congratulations, you recognized the logic flaw I purposely presented to make a point.
A spring is like gravity, it gives back nearly all of the energy that it took to compress it when the spring is decompressed. The energy it took to compress the spring is returned to the system while the valves are closing, there are periods of time when the camshaft is driving the engine instead of being driven by the engine.
A perfect spring would return all of the energy but a real world spring will have some hysteresis even if it’s very little.
Gravity on the other hand is perfect, it returns all of the energy given to it when a mass is lifted up in the air and then returned.
One of the biggest logic flaws stated by desmodromic fan boys is the idea that constantly compressing those heavy springs is inherently parasitic, ignoring the fact that springs return the energy needed to compress them to the camshaft during valve closing.
The force of the compressed springs does add a small amount of friction to the cam rotation but even that can be minimized by using roller lifters.


#129

B.L.E
Please read the link I provided before you answer.
I’m not pro or against desmodromic valvetrains, I just have no use for them.


#130

technical reasons:
manual shifts are less problematic as they don’t break as fast as the automatic ones
manual shifts are less costly to repair in case they do break up
your car is consuming less with manual shift (of course if you know how to properly use it)
other reasons: oral steroids
people with automatic shifts are not in full control of the car, you can’t slow down with your transmission and many other things in this matter
you definitely can’t drift
without launch control, you can’t properly launch a good start in case of drag race compared to manual shift
many other reasons why there are many 1000+ hp with manual transmission


#131

Nope, in actual use the mileage is better with the exact SAME number of gears. case in point: 2013 Mustangs, both V6 and V8. Both have 6 speed manuals available and both have 6 speed auto’s available. Both automatic cars get higher MPG’s in the city cycle and the same in the highway cycle than the manuals. That means the composite MPG rating is higher for both automatics.

And that isn’t the only example I can find.


#132

I have read the link you provided including this part.

This section’s factual accuracy is disputed

I have known about desodromic valves since the 1970’s when Ducati was using them in their bevel gear shaft driven cam single cylinder motorcycles.

Valve spring metallurgy has advanced to the point where desmo valves are more a complication than an advantage and I also think that not needing to compress a heavy spring is mostly an imaginary disadvantage since the spring returns the energy to the system upon closing.


#133

It’s not the number of gear ratios that’s important, but the range of ratios available, or the depth of gearing.
A manual and an automatic may both have six gear ratios, the the two highest ratios on the automatic will usually be overdrives that are so tall that they are used only on downgrades and during deceleration or tailwinds. The sixth gear on the manual may have the same gear ratio as the 4th gear on the automatic.
Many manual six speeds will have no overdrive ratio and while cruising at 60, the engine rpm will be so high that it has the driver checking to make sure he’s actually in 6th gear.
A lot of 6 speed automatics actually shift down out of the overdrive gears in order to be able to reach the car’s top speed, the overdrive ratios being too tall to allow the engine to rev to the rpm it needs to make the horsepower needed to achieve the car’s top speed.


#134

I know that, I was replying specifically to chunky’s assertion that the number of gears is the significant point in the discussion.

I agree, there are far more variables. Total gear span can be one but can also be deceptive. The example I used, the '13 Mustang, the automatic

A '13 Mustang GT automatic has the a greater total ratio in first gear (first times final drive) with a 3.15 final drive and 4.17 1st gear as the 6 speed manual with its 3.31 final drive and 3.66 1st gear. Then the unlocked convertor adds torque and engine RPM to the mix for a stronger acceleration although limited by traction.

Final overdrive in 6th for both cars is nearly identical and the EPA MPG’s are the same. Yet the automatic gets better city fuel economy although it will not put down as much rear wheel HP on a dyno as the manuals. That says the automatic is not as efficient overall as the manual but in operation, it provides better mpg’s.


#135

All of my cars have had stick shifts. My wife’s have mostly been automatics, but she drives stick with no issues.

It’s like computers–I want both the car and the computer to do as it’s bloody well told, and not try to second-guess me.

Plus I save money whenever I rent a car in Europe. :wink:

Cheers

PhilH


#136

Gravity somehow magically causes a Pinewood Derby car that has been lifted and placed at the top of a sloped track to roll to the bottom of the track when released. I am not an engineer so that explanation is sufficient for me. If I were an engineer I would be driving trains.


#137

you should think a little more about what force ‘squeezes’ protons together in the thermonuclear (fusion) reaction – the mass of all the molecules in the sun brings them together under the force of its own gravity

no idea what you mean


#138

Gravity only acts as a pressure vessel allowing the high pressure and temperatures needed for this reaction, but it is the reaction that provides the energy, not the gravity. You might say that gravity is the catalyst for the reaction.
Inertia can also provide the pressure, in the case of a hydrogen bomb.


#139

call it “a pressure vessel” if you like, but gravity is the force driving the fusion reaction – without that gravity, there is no reaction

so no gravity means no reaction, which means no sunlight


#140

But gravity is not the source of the energy released. Gravity is more like the match that lights the dynamite fuse.