# Why Manual > Automatic?



## FenPhen (Jan 13, 2004)

Fast Bob said:


> If you do the math (214x4.35x2.93), you will see that the manual trans model will give a maximum of 2727 lb./ft of torque (at maximum multiplication). Assuming the torque converter provides a multiplication factor of 2.5, and again, doing the math, (214x2.5x3.45x3.38) you will find that the result is a *staggering* 6238 lb./ft. of torque.
> But it`s not all a free lunch....due to fluid & pumping losses there`s a loss of efficiency that eats up some horsepower, and by about 70 mph, the torque converter loses all advantage over it`s stick counterpart.


The caveat about a torque converter's multiplication effect is that it is only there when the engine is spinning much faster than the transmission (standing on the brake pedal and bringing the revs up close to stall as you describe).

The torque converter can lose its advantage before 70 mph, basically when the transmission speed approaches the engine speed and the stator starts to free-wheel.


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## hector (Jul 14, 2003)

FenPhen said:


> The caveat about a torque converter's multiplication effect is that it is only there when the engine is spinning much faster than the transmission (standing on the brake pedal and bringing the revs up close to stall as you describe).
> 
> The torque converter can lose its advantage before 70 mph, basically when the transmission speed approaches the engine speed and the stator starts to free-wheel.[/QU
> 
> given what you and fast bob have described, overall in daily driving would you say that one would be experiencing significant torque multiplication or is it reallly just a 1st gear brake-torqueing dragstrip phenomenon?


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## Moderato (Nov 24, 2003)

phita23 said:


> Why Manual > Automatic?


Simple, the answer is: Less people you know will ask to drive or borrow your car.


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## Fast Bob (Jun 4, 2004)

hector said:


> FenPhen said:
> 
> 
> > The caveat about a torque converter's multiplication effect is that it is only there when the engine is spinning much faster than the transmission (standing on the brake pedal and bringing the revs up close to stall as you describe).
> ...


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## jsc (Sep 3, 2003)

hector said:


> given what you and fast bob have described, overall in daily driving would you say that one would be experiencing significant torque multiplication or is it reallly just a 1st gear brake-torqueing dragstrip phenomenon?


Basically at low revs you will get a torque multiplication effect similar to a lower gear until the fluid stops shearing between the rotor and stator, this gives the "disconnected" feeling of an automatic transmission, it has two side-effects - a continuously variable gear ratio within a small range and a buffering effect that cushions the driveline. Once the stator and rotor spin at the same speed, there is no torque multiplication.

Really the torque multiplication of the torque converter has limited practical use, if you try to use this effect for increasing the vehicle performance you can easily overheat the transmission (torque braking for more than a couple of seconds can easily do this as you are dissipating the engine power by shearing the transmission fluid and converting most of the power into heat).


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## flashinthepan (Jul 25, 2003)

phita23 said:


> Why, when all other conditions are identical, will a stick shift be faster than an automatic?


Simple terms:
Typically a Manual works the motors full potential slightly better. However Mercedes gets some monster numbers from their Automatics.


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## Test_Engineer (Sep 11, 2004)

OK guys (and gals if any in this thread), I test cars for a living and I can shed a little light on this subject. 

Most of the common things have been covered, but I will just make a list that covers almost everything.

Weight: Usually about 30-40 kg is added to the vehicle when using an automatic tranny. Heavier is always slower: Strike 1 for the AUTO.

Drive train loss: An automatic transmission uses alot of fluid and pressure diferentials to shift the gears, which results in loss of energy in the form of heat and fluid shear. You have a torque convertor which is basically 2 fans submerged in oil that transfer the power from one side to the other. The torque converter can however go into a lock-up mode, which does make it a direct drive and negates the power loss due to fluid power transfer, although this is usually only in low torque situations. The other big loss is just the number of gears in an automatic. Every time you add another gear to a mechanism, you add more friction and heat causeing a loss of energy. A manual tranny has far less gears and no fluid controls, so it loses much less energy when it is transfering the power. Strike 2 for the auto!

The engine: Typically the engines are different from an automatic to a manual car of the same model. The major difference is usually in the camshaft. Each transmision uses/needs torque at different areas of the powerband to operate as best and as linear as possible. So you ask why the cars have the same HP....they don't... that number is just a catlog number and is an average of it's production(autos and manuals). Strike 3 for the Auto.

Engine calibration: Since the engines are usually different, obviously the calibration is different. Even IF the engines are identical, the automatic needs a much smoother power delivery for it to be linear. In an auto the ECU has to control(limit) the engine more to ensure smooth shifts without shift-shock. In a manual, this is all up to the smoothness of the driver. Now, this is changing as Electronic Throttle Control,"drive-by-wire", is becoming more common in vehicles. The gas pedal is actually calibrated much differently between a manual and an auto. AND, the throttle is calibrated for each gear as well. What this all means is that it is not a 1:1 ratio between pressing the gas pedal and the actual opening of the the throttle body, and the calibration is much more conservative on the automatic, because it needs that very smooth power delivery. Most new cars can even determine which gear a manual transmission is in. So basically the the throttle response and throttle actuation is more conservative on a an automatic, creating a slower car. Strike 4 for the auto.

Those are the big ones, so you can see how the auto will always be slower.


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## FenPhen (Jan 13, 2004)

Test_Engineer said:


> Those are the big ones, so you can see how the auto will always be slower.


Nice info. 

What about some cars like Camaros, which I'm told are faster with automatics for drag racing because they "handle torque better"...? Is that true?


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## Fast Bob (Jun 4, 2004)

FenPhen said:


> Nice info.
> 
> What about some cars like Camaros, which I'm told are faster with automatics for drag racing because they "handle torque better"...? Is that true?


Nowadays, drag racing is all about consistency.Back in the good old days, guys ran "heads up", that is, they left the starting line at the same time, and whoever got to the finish line first was the winner. These days, many people engage in what`s known as "bracket racing", where you have to predict your elapsed time (ET) before you run.Let`s say you choose 14.1 seconds as your bracket....you`re running against a guy with a 14.6 bracket....he gets the green light .5 seconds before you....first one to the finish line wins....but only if you don`t "break-out", or run faster than, your bracket time. An auto trans gives you a higher level of consistency in this situation.

Regards,
Bob


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## Moderato (Nov 24, 2003)

Fast Bob said:


> These days, many people engage in what`s known as "bracket racing", where you have to predict your elapsed time (ET) before you run.Let`s say you choose 14.1 seconds as your bracket....you`re running against a guy with a 14.6 bracket....he gets the green light .5 seconds before you....first one to the finish line wins....but only if you don`t "break-out", or run faster than, your bracket time. An auto trans gives you a higher level of consistency in this situation.
> 
> Regards,
> Bob


 :tsk:


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