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Old 08-22-2008, 08:32 PM   #21
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Originally Posted by stevenh View Post
Lol, I was TOTALLY ******* around with my responses. Good explanation though
Do not come in here with 16-posts and think we're going to put up with it. When you come into our house and **** with us, expect me to come to your house and adjust your attitude. Now I'm going to the gym to put up more weight than you've ever seen in your life, I recommend you fake your death before I get back because you do not want a dose of myself, pissed off.
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Old 08-23-2008, 12:08 AM   #22
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Originally Posted by patsmx5 View Post
The motor produces a torque. The clutch couples the engine to the transmission.



Any time you accelerate in the positive direction (we assume forward to be the positive direction) with the transmission in gear, torque is transmitted from the flywheel/pressure plate to the clutch disk. The amount of torque transfered is whatever the motor is developing irrelevant to what what gear you're accelerating in. Torque multiplication occurs in the transmission, which is AFTER the clutch. Maximizing torque at the wheels is the objective. That's why we have a transmission.

For a given rpm, the engine has much more load on it in a higher gear and thus develops more torque in a higher gear. That's why a borderline pressure plate cannot hold the torque in a higher gear but can do so in a lower one.

Torque is a somewhat direct function of manifold pressure, which in turn is an almost linear function of load. In fact the ECMs on newer cars are all calibrated with torque as the y-axis, not map or maf. its just easier to calibrate the fueling/spark with the million different loads (a/c, ps, electrical loads etc.) in a newer vehicle using torque as the parameter. The ECM has a lookup table of the manifold pressure or airflow vs. torque stored in it, and it references that to find the torque from each value of manifold pressure.

The point is, MAP is a reliable measure of torque, and if you've noticed in your logs, the MAP for a given rpm at WOT (or any throttle for that matter) is lower for lower gears. And therefore, less torque is developed in a lower gear for a given rpm.
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Old 08-23-2008, 12:23 AM   #23
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So does the plain take of or nut?
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Old 08-23-2008, 12:24 AM   #24
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Originally Posted by The_Pipefather View Post
For a given rpm, the engine has much more load on it in a higher gear and thus develops more torque in a higher gear. That's why a borderline pressure plate cannot hold the torque in a higher gear but can do so in a lower one.

Torque is a somewhat direct function of manifold pressure, which in turn is an almost linear function of load. In fact the ECMs on newer cars are all calibrated with torque as the y-axis, not map or maf. its just easier to calibrate the fueling/spark with the million different loads (a/c, ps, electrical loads etc.) in a newer vehicle using torque as the parameter. The ECM has a lookup table of the manifold pressure or airflow vs. torque stored in it, and it references that to find the torque from each value of manifold pressure.

The point is, MAP is a reliable measure of torque, and if you've noticed in your logs, the MAP for a given rpm at WOT (or any throttle for that matter) is lower for lower gears. And therefore, less torque is developed in a lower gear for a given rpm.
So in summary you've concluded if I push the gas pedal less the motor makes less torque. Sure. Less air, less fuel, less torque. Makes sense to me.

The guy I've been quoting thinks gearing affects the torque the clutch "sees". This, is not correct. The torque the motor develops is what the clutch sees. No more, no less. If you make 100 ft lbs. of torque at a given RPM, that number does not change regardless of gearing. You wind the motor through all the gears using your 100 ft*lbs as you race from 1st through 5th gear. That number doesn't change as you shift gears. That's my point. Sure the torque it "sees" changes when you mash the gas.
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Old 08-23-2008, 12:41 AM   #25
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Thats alot of info to digest at one time...but I'll try.

BTW,I luv your quote...That thread made me laugh my *** off!!!
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Old 08-23-2008, 12:22 PM   #26
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Originally Posted by hustler View Post
When you come into our house and **** with us, expect me to come to your house and adjust your attitude. Now I'm going to the gym to put up more weight than you've ever seen in your life, I recommend you fake your death before I get back because you do not want a dose of myself, pissed off.

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Old 08-23-2008, 04:34 PM   #27
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This feels like it's getting to be a thread jack, but I swear it is related to the OP

patsmx5: I guess I'm not explaining myself correctly. It looks like from your responses that you are thinking from the point of view of engine torque to clutch (am I right?). My point of view is constant acceleration regardless of velocity to torque on the clutch. I think we are arguing opposite ends of the same argument...and are in agreement. Now I just have to clarify my side of the story:

<my argument>
The clutch can only hold a finite amount of torque. The torque the engine puts out--and the clutch has to hold--to accelerate the car at the same rate is different depending on what gear the car is in.

Say I accelerate linearly at 20mph/min starting from 2000 RPM to 4000 RPM (think only of rate of acceleration, not initial and final velocity of the car, or speed, or anything like that). In first gear there is less torque the clutch has to hold than if I accelerate at 20mph/min in 5th gear. The overall speed is different and the required torque is different, but the rate of acceleration of the car is the same and the RPM range is the same.


When the slipping clutch's comprimised static friction coefficient is reached, the clutch will no longer be able to hold the torque and will slip. Since it takes a higher amount of torque in 5th than it does in 1st, the clutch is more likely to slip in 5th than in first for a given rate of acceleration.

Another way to look at what I am saying is: it's easier to turn the input shaft to turn the wheels in first gear than it is in fifth. Ignoring final rotational speed of the wheels, but not ignoring the rotational speed of the motor, that means it requires less torque to accelerate the wheels at a given rate in first than it does in fifth at that same rate.
</my argument>

All that aside, it is way easier to get a badly slipping clutch to slip in fifth than in first. I have first hand experience with that.
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Old 08-23-2008, 04:44 PM   #28
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Quote:
Originally Posted by miatamoxie View Post
This feels like it's getting to be a thread jack, but I swear it is related to the OP

patsmx5: I guess I'm not explaining myself correctly. It looks like from your responses that you are thinking from the point of view of engine torque to clutch (am I right?). My point of view is constant acceleration regardless of velocity to torque on the clutch. I think we are arguing opposite ends of the same argument...and are in agreement. Now I just have to clarify my side of the story:

<my argument>
The clutch can only hold a finite amount of torque. The torque the engine puts out--and the clutch has to hold--to accelerate the car at the same rate is different depending on what gear the car is in.

Say I accelerate linearly at 20mph/min starting from 2000 RPM to 4000 RPM (think only of rate of acceleration, not initial and final velocity of the car, or speed, or anything like that). In first gear there is less torque the clutch has to hold than if I accelerate at 20mph/min in 5th gear. The overall speed is different and the required torque is different, but the rate of acceleration of the car is the same and the RPM range is the same.


When the slipping clutch's comprimised static friction coefficient is reached, the clutch will no longer be able to hold the torque and will slip. Since it takes a higher amount of torque in 5th than it does in 1st, the clutch is more likely to slip in 5th than in first for a given rate of acceleration.

Another way to look at what I am saying is: it's easier to turn the input shaft to turn the wheels in first gear than it is in fifth. Ignoring final rotational speed of the wheels, but not ignoring the rotational speed of the motor, that means it requires less torque to accelerate the wheels at a given rate in first than it does in fifth at that same rate.
</my argument>

All that aside, it is way easier to get a badly slipping clutch to slip in fifth than in first. I have first hand experience with that.
Correct. I agree with you 100% on all of that. What you say now makes sense. Did you make those drawings?

Johndoe said:
Quote:
For a given rpm, the engine has much more load on it in a higher gear and thus develops more torque in a higher gear.
This is wrong. I think you're trying to say what miatamoxie just said. The motor does not magically develop more torque just because you change the gearing. Now if you give the motor more fuel and air then it develops more torque.
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Old 08-23-2008, 05:04 PM   #29
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This thread gives me gas.
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Old 08-23-2008, 07:23 PM   #30
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yep, made those drawings in Open Office Paint.
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