Myth? Torque converter torque multiplication

[Marlin]

Sorry, I know this isn't FSAE related. How can a torque converter increase torque?
http://www.tciauto.com/tech_info/torque_converters_explained.htm

I've read that they can many times over the years from other sources, but I don't believe them.

The TC is only mounted to the crankshaft so it doesn't have any reaction forces like a gear reducer has. An effective momentary torque multiplication could happen if the crank was decelerated rapidly, but I don't think this happens either. What am I missing?

Thanks,
Marlin

[Marlin]

Sorry, I know this isn't FSAE related. How can a torque converter increase torque?
http://www.tciauto.com/tech_info/torque_converters_explained.htm

I've read that they can many times over the years from other sources, but I don't believe them.

The TC is only mounted to the crankshaft so it doesn't have any reaction forces like a gear reducer has. An effective momentary torque multiplication could happen if the crank was decelerated rapidly, but I don't think this happens either. What am I missing?

Thanks,
Marlin

[Timmay!]

In my 97 Dodge Dakota, I have a 2800 stall Precision Industries converter with a 2.5 rating. With the tranny "locked" in 3rd gear on the dyno, I could get some pretty insane torque numbers by simply "flashing" the converter at a low speed... (I usually nail it at 40 on the dyno for a faily good 3rd gear pull) My numbers were 426RWHP/478RWTQ... but the torque peak was once the converter "flashed" and fell rather quickly, and the HP climbed normally (boosted).

With my experiences in many different stalled (converter) vehicles, I think the best way to describe what "torque multiplication" is would be to say, the higher the rating, the "Harder" the car will launch (better 60' times). 9/10 times a higher Torque Multiplication rating will hurt your top end due to it being slightly less efficient.

So, for example...

Joe Schmoe has a 99 F-Body with an LS1 with an automatic tranny. He puts 2 identical Acme 3000 stall converters, with the exception of one is rated a 1.8 and the other is 2.5 for the torque multiplication, in his car and tests them.

His track times are:
(With the 1.8)
60' - 1.78
1/4 - 12.6 @ 108MPH

(With the 2.5)
60' - 1.65
1/4 - 12.34 @ 105.8 MPH

This may be a pointless post, but its how I can best explain in real world terms...

[rkellz]

The Bosch Automotive Handbook contains a good description of the device. The multiplication comes via the fact that you have a crank mounted pump putting energy into a fluid at one angular velocity and a transmission mounted turbine taking it out at another lower angular velocity (up to stall when the two essentially lock together). Simple conservation of angular momentum dictates that more force has to be applied at the low-speed side.

Also check out the how-stuff-works description, although I think they have one of the graphics labled backwards.

[Chuck Maddocks]

you think torque converters are hard to understand

check this out : hydristor (http://www.hydraulicspneumatics.com/200/GlobalSearch/Article/False/6527/hydristor)

variable displacement pump + variable displacement motor = 95% efficient cvt

scroll to the bottom where it says "what's in store" if you don't really care how it works, just how it can be used in an automobile. well he doesn't explain how it can be used in a car, but use your imagination. a 95% efficient transmission? slick

works similar to a torque converter, but is much more efficient. if someone could get it into a fsae car, it would be super sweet. it might not make your car faster, but it would be sweet. there are other advantages to this tranny, you'll have to research them and gain a little understanding of hydraulics. for example, if you use the brakes to pump fluid into an accumulator, you can release this fluid back into the hydraulic motor for added acceleration.

i heard they put one in a ford expedition and it got 40 mpg and 0-60 in 5 seconds by storing the fluid like i said above

[CrazyDave]

You can also think of it in the following terms. (wrong terms, starting at result and thinking to causes, but its effective)

The device has a efficiency number that determies the power lost through the device.

The power at each end is determined by the input power and efficiency.

Fix the engine speed and the resulting output speed is dependant on road speed. therefore at low road speeds the torque is higher and at high speeds the torque is lower. (power=Force*speed)

(this is why you can bring the engine speed up very high at a standstill, the torque converter becomes inefficient and the brakes and resist the output force.)

So the peak torque ratio is the ratio of input to output regardless of speeds. You should really get your hands on a chart(map) that describes a torque converter. However every time i saw one it was a complete system map ie. 1st 2nd 3rd gears were shown as well as torque converter lockup and convert modes.

[drivetrainUW-Platt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Timmay!:
In my 97 Dodge Dakota, I have a 2800 stall Precision Industries converter with a 2.5 rating. With the tranny "locked" in 3rd gear on the dyno, I could get some pretty insane torque numbers by simply "flashing" the converter at a low speed... (I usually nail it at 40 on the dyno for a faily good 3rd gear pull) My numbers were 426RWHP/478RWTQ... but the torque peak was once the converter "flashed" and fell rather quickly, and the HP climbed normally (boosted).

With my experiences in many different stalled (converter) vehicles, I think the best way to describe what "torque multiplication" is would be to say, the higher the rating, the "Harder" the car will launch (better 60' times). 9/10 times a higher Torque Multiplication rating will hurt your top end due to it being slightly less efficient.

So, for example...

Joe Schmoe has a 99 F-Body with an LS1 with an automatic tranny. He puts 2 identical Acme 3000 stall converters, with the exception of one is rated a 1.8 and the other is 2.5 for the torque multiplication, in his car and tests them.

His track times are:
(With the 1.8)
60' - 1.78
1/4 - 12.6 @ 108MPH

(With the 2.5)
60' - 1.65
1/4 - 12.34 @ 105.8 MPH

This may be a pointless post, but its how I can best explain in real world terms... </div></BLOCKQUOTE>

Joe should buy a LS1 with a 6 speed next time.....

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