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The Poi
 
Oh my god. I hate you guys. Seriously. It doesnt matter what gear you're in, it doesnt matter what final drive you have. Only two things matter, the torque the wheels produce, and that fancy clippy thing they put on your spark plug wire. That will take care of all your gearing woes. Its simple math to determine how much torque the motor is producing at the wheels from how much torque the wheels are making and how fast the motor is spinning. The only "wildcard" is an auto cars torue converter, where at low RPM, the effects of the stator increase torque asymmetric to the engine speed. Once the stator begins to freewheel (at around 2k i suppose) the whole shebang works as expected. "wheel torque" measures not torque multiplication, but the loss of toruqe from the engine to spin the druivetrain at any given speed. In conclusion I hate you guys.
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Old 08-30-2004, 02:58 PM The Poi is offline  
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Old 08-30-2004, 02:58 PM prak is offline  
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#122  

demosh
 
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hi, dumbass

300 wheel torque does NOT take drive ratios into account. that's why you drive the fucking car to the 1:1 gear and if there's no exact gear the computer's programmed to adjust for each particular car

And the number you get out isnt wheel torque, but rather engine torque - TWO COMPLETELY DIFFERENT QUANTITIES!
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Old 08-30-2004, 02:58 PM demosh is offline  
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#123  

SFC
 
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Originally Posted by demosh
Er

At the engine it is making 194 lbs-ft. In first gear, that translates to 2653 lbs-ft at the wheels. In a 1:1 gear, it makes for 741 lbs-ft at the wheels.

At the torque peak, this particular engine is spinning at 2100 rpm (IIRC, but the actual number isnt relevant). In first gear, the wheels are spinning at 2100 rpm / 3.58 / 3.82 = 154 rpm


you do realize they say wheel torque because there's loss in the drivetrane from the "flywheel torque" right? The same reason they say "wheel horsepower" which going by your standards your dad's car would be making somewhere near 900HP... HP is derived from torque....
Old 08-30-2004, 02:58 PM SFC is offline  
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#124  

SFC
 
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Originally Posted by demosh
And the number you get out isnt wheel torque, but rather engine torque - TWO COMPLETELY DIFFERENT QUANTITIES!


it ISN"T engine torque, it's WHEEL torque, there's drivetrain loss...
Old 08-30-2004, 02:59 PM SFC is offline  
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#125  

needsmorefrink
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this thread needs to be locked, you guys are just bickering like women now.
Old 08-30-2004, 02:59 PM needsmorefrink is offline  
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#126  

SemperFly
 
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Originally Posted by Tex Arcana
Then the numbers they spew out are not "wheel" numbers.

Let's try this again, using my truck as an example: 450 ft-lbs of torque at the crank, thru 1:1 in the tranny, assuming no losses and a locked torque convertor, thru the 1:3.73 rear-end ratio (which will multiply the torque 3.73 times, ignoring the differential), then thru the wheels (which will divide the torque by 1.19, becasue it's over a lever arm of 1.19 ft), which will produce 757 ft-lbs at each wheel, or a total of 1514 ft-lbs.

but the dyno sez 425 ft-lbs at the wheels.

Discrepancy.

So where is the error?
Chassis dynos are adjusted like that to show you the final numbers after drivetrain loss. Gear multiplication and reduction is not considered drivetrain loss. The dyno says 425 because of you had a rear end ratio of 1:1, a gear ratio of exactly 1:1, and every other ratio at 1:1 so that your tires were rotating at the exact same speed as the flywheel, your power output would be 425.

Chassis dynos are not there to measure how torque is affected by gears, they're there to measure the amount of drivetrain loss you're suffering.
Old 08-30-2004, 03:01 PM SemperFly is offline  
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#127  

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this thread needs to be locked, you guys are just bickering like women now.

I'll scratch your eyes out bitch

Old 08-30-2004, 03:01 PM Why_Ask_Why is offline  
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#128  

LagPenguin
 
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Jesus christ this is fucking retarded. Example: take your 400tq small block chevy with 3.73:1 gear ratio rear. Now put 4.11:1 in it. Does that change the torque your motor is making? NO!!!! It changes the RPM at which the rear wheels spin in relation to the output shaft of the transmission. Your 400tq small block is sadly STILL a 400tq small block, you just get to feel that torque sooner because RPMs are increased. Please end this shit.
Old 08-30-2004, 03:01 PM LagPenguin is offline  
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#129  

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Old 08-30-2004, 03:02 PM SebG is offline  
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#130  

SemperFly
 
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Quote:
Originally Posted by demosh
And the number you get out isnt wheel torque, but rather engine torque - TWO COMPLETELY DIFFERENT QUANTITIES!
No, it's wheel torque because the whole point of a dyno is to show you how much power you're putting out after drivetrain loss.
Old 08-30-2004, 03:02 PM SemperFly is offline  
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#131  

demosh
 
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Originally Posted by SFC
your dad's car would be making somewhere near 900HP... HP is derived from torque....

No, it wouldnt. Horsepower depends on torque and speed. If torque is 3.82 times more at the wheels, and the wheel revs are 3.82 times less, horsepower is the same.
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Old 08-30-2004, 03:02 PM demosh is offline  
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#132  

Tex Arcana
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Quote:
Originally Posted by FlyNavy
You're fucking wrong. It does not make for 741ftlbs at the wheels. You can throw math and physics all you want but when the numbers are fucking MEASURED the final drive ratio is taken into account by the dynos computer and adjusted.

You put your fucking Saab on a dyno and you will never see 741 ft lbs. Period. Ever.

Why the HELL are you talking about first gear? Who gives two flying shits about first gear when all cars, every last fucking one, is always measured in the gear closest to 1:1.

Alright, man, stop with the obsceneties: he's making a valid point. He did it to me in the other thread, and is doing it here.

He's pointing out that output at the wheels is based on the gear ratio of the drivetrain when the power is measured.

The dyno's only measure the acceleration of a set of super-heavy drums, then translate that acceleration to a force measurement, and then calculate the numbers. I need to find and post the dyno article I read, about how one dyno to another will show all sorts of discrepancies, becasue of changing conditions and calibrations.

What he's asking, and waht I am as well, is how in the hell do the numbers end up so far off? If my dyno is reporting "crank" numbers, then something is VERY fucking wrong. If they are reporting WHEEL numbers, then something is still not right, because the torque numbers are multiplied thru the rear end.
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Old 08-30-2004, 03:03 PM Tex Arcana is offline  
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#133  

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Old 08-30-2004, 03:03 PM SemperFly is offline  
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#134  

SemperFly
 
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Quote:
Originally Posted by Tex Arcana
Alright, man, stop with the obsceneties: he's making a valid point. He did it to me in the other thread, and is doing it here.

He's pointing out that output at the wheels is based on the gear ratio of the drivetrain when the power is measured.

The dyno's only measure the acceleration of a set of super-heavy drums, then translate that acceleration to a force measurement, and then calculate the numbers. I need to find and post the dyno article I read, about how one dyno to another will show all sorts of discrepancies, becasue of changing conditions and calibrations.

What he's asking, and waht I am as well, is how in the hell do the numbers end up so far off? If my dyno is reporting "crank" numbers, then something is VERY fucking wrong. If they are reporting WHEEL numbers, then something is still not right, because the torque numbers are multiplied thru the rear end.
And then after those numbers are multiplied through the rear end, the computer throws those numbers into a calculation that includes the exact gear ratio and rear end ratio and then spits out the number that you would have if you had a 1:1 ratio from the engine to the wheels.
Old 08-30-2004, 03:05 PM SemperFly is offline  
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