92BlAcK_RSLO3

Hello everyone.

I hope someone could help me with this doubt I have about how torque get to the weels ot of the cranck.

I know The Torque Conv, sometimes multiply the torque (or at least that is what I have understanded)

Then every gear in the gearbox have some friction and each multiply the torque in a different amount.

For example a first gear wit a 3.1 relationship will multiply the crank torque by that amount minus the loses of that especific gear correct? (Anyone know of the specific numbers for a T5, T56 or 4L60)

Then the driveshaft transmit this torque (I dont know if its relationship is exactly 1.1 or if there is any lose) to the rear where it get multiplied by the final gear by its amount a 2.74 multiply it by that amount minus some loose by friction, then that torque is aplied to the weel-tire and get some relationship using the external diameter of it (How that work??? I should compare the external diameter of the tire with what diameter to know the relationship)

One thing I readed a week ago told me that you get different torque in each different gear, and that each gear have its own looses, so why in dynos you only get one torque curve, instead of having one torque curve for each gear (I have seen that kind of curves on motorcycle magazines)

Well I hope someone can help me with this.

Thanks all.

RB83L69

Most of the time people measure cars on the chassis dyno in whatever trans gear is "direct", i.e. no gears. And, the dyno readings are "normalized" by comparing the engine RPM to the dyno RPM, to eliminate the issue of what gear the car has, and instead create an apples-to-apples comparison. If you wanted to, there's no reason you couldn't do what you're talking about, it's just not generally a very useful thing to do with a car because the losses don't change much according to what gear they're in, other things have far more effect.

Torque is measured in ft-lbs; you'd want to use a tire of 24" (1 ft radius) for your calculations.

92BlAcK_RSLO3

Ok let me see if I can Understand this.

When you acelerate in first gear from standing with a gear like 3.3 to one you acelerate much faster than if you acelerate in the same situation but in a second gear of say 1.8 to one.

The more torque you have at any given velocity the faster you can acelerate a given weight (or you can conter act a stronger force), So the function of lower (Than 1 to 1) gears is to multiply the torque you have in the weel, so say when you put a lower gear on the final gear is like putting a long tube on a wrench, you are apliying the same streng to the end of the tube as you where apliying to the end of the wrench, but you end with more torque. Aint that right?

So in each gear you will have similar curves but with different amounts of torque as gears multiply it, The same is with tires if you put a larger than stock diameter tire on a car you get less torque transmited to the ground than with a stock tire.

Kingtal0n

torque is multiplied by gearing and torque converters.
this is how it was explained to me in a book about automatic transmissions, its overly simplified but i think it helps get a point across.
lets say 200 Ft. Lbs of torque at our engine at 1400 rpms, but we are in first gear with a Th350 tranny with 2800 Stall converter.
lets round off gearing and torque multiplication.
2.50 X 200 = 500 ft. lbs. for gearing.
now we go for torque multiplication. lets say 2:1 for simplicitys sake. 500 X 2 = 1000 ft lbs.

now rear gearing. 3.73's you say? okay.
1000 X 3.73 = 3730 Ft lbs. - 18% drivetrain losses = 3059 Ft Lbs. of torque at the wheels in first gear.

lets do the same for a th350 with 2.73 gearing (stock stuff)
2239 Ft. lbs of torque at the wheels. its easy to see how a simple gear swap can affect the acceleration of a vehicle.

obviouselly a converter cant nail it 2:1 right off idle without some "help" from a transbrake.
this is with only 200 ft. lbs., the differences become huge as you move up in the engine output. it also explains why people launching with a transbrake can pull the wheels off the ground so easilly if they hook up, they are 3:1, somtimes 4:1 engine torque output to the rear end, which further complicates things.

92BlAcK_RSLO3

So when people change the gearin of the rear end and the Converter is to put the maximun torque to the whell at launch.

So a 2800 stall converter multiplay the torqe too, but when it attain the maximun torque multiplication? at that speed 2800??

I will see in Howstuffworks the info about torque converters, to see if I can find exaclty how they work, there is any reading material anyone know off?

Thanks for the help. I was not taking in account the effect of the torque converter.

I wish I can understand this a little, So i just dont have to just gess whats going on in my car. I need to understand it, Im very bad at taking advice without explanations, I like to understand how car stuff really works instead of asking everytime I want to change anything in my car. Wich piece is the right for this?.

Kingtal0n

<b>So a 2800 stall converter multiplay the torqe too, but when it attain the maximun torque multiplication? at that speed 2800??
</b>

According to the books, "How to Rebuild your Th350" and "Rebuilding Torque converters" (or somthing like that) it explains that;

the torque multiplication of a torque converter depends on EVERYTHING ELSE in the drivetrain. for instance a 2800 Stall converter may only multiply torque 2:1 with a 2.77 rear end, but when matched to a 3.73 rear end, it may multiply torque 3:1 because the momentum of the engine builds faster because it no longer has to push as hard to get the car moving.

it also depends on how the converter was made, what size it is, whats it got in it... etc...
a 10" converter is more effective at multiplying torque than a 12" is, for several reasons, the main 1 being that its a lot lighter than 12". the technology of 10" and 12" converters is still old, the new line of 9.5" converters are made totally different (so im told). I dont have much info on them, other than they are perfect for street because they multiply torque no matter what the output of the engine is, and can change depending on situation. example: 2800 Stall 9.5" converter can still multiply torque at 1400 RPMS under light throttle from a stoplight, giving the driver excellent fuel economy by not "bypassing" the flash RPM diectly to the stall RPM. however, bring the output of the engine up a notch (half/full throttle) and the converter stalls appropriatelly to its stall speed, making full multiplication etc...

I dont know much im just going by what I read. I could be wrong here or there, but im pretty sure about most of it. heh. As a general rule of thumb, for overdrive trannys, the new 9.5" converters are the way to go for sure. especially for the street. can you tell im biased?

383backinblack

a torque converter can provide an immense multiplication of torque at very low rpms, but its fleeting......when the converter first starts to transfer torque, it can be around a 2:1 multiplication....however, as soon as rpm starts to rise, this multiplication effect rapidly falls to zero (its an exponential function of RPM)

but like you guys said, the amount of that multiplication is dependant on alot of other variables, as is drivetrain loss.

but as the engine builds rpm, torque mulitplication always falls to zero, quite rapidly. makes sense if you think about it, otherwise everyone would say f*ck manuals. What makes a torque converter do what it does involves some rather complex fluid dynamics.....but someone else already figured that crap out hehe

92BlAcK_RSLO3

So a torque converter work "Like" two gears connected by oil so when the difference betwenn the two parts (rotation) is bigger there is more torque multiplication, but as the two parts beggin aproaching the same speed you get no torque multiplication?

I know that torque converter locks exist because when the input and output speed is almost the same you actually loose some torque couse of what happend with the oil inside the torque converter case.

383backinblack

well its alot more complicated than that....but thats not a bad way to look at it. its different than gears obviously because its a fluid coupling....and its not a direct relationship its exponential (growing by exponents) but yes thats essentially what happens.

torque converter lockup is a way of maximizing top speed output and fuel mileage.....

because it is a fluid coupling there is a degree of slip between the input and output....therefore the lockup locks the two parts together allowing no slip (like a manual clutch)

92BlAcK_RSLO3

Well yes, I tryed to simplifi it couse of all the terms I would need to use couse of my very bad english.

I think I can understand how one part of the converter transfer movement to the other part, but i did not understanded that you could multiply the torque by having different speeds on both parts, as it is with belts and gears.

383backinblack

yup, the torque multiplication is really a phenomena of fluid dynamics, and is dependant on the design of the internal components of the converter. but you seem to have basic idea of how it works.

check out this link, everything you wanna know about a torque converter http://www.howstuffworks.com/torque-converter.htm