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SemperFly
 
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Look, how complicated is this to understand? Dynamometers are hooked up to computers that calculate and adjust for the discrepancy in gear ratios. Even without gears you still have drivetrain loss and THAT'S what dynos are built to measure.
Old 08-30-2004, 03:07 PM SemperFly is offline  
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Tex Arcana
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Quote:
Originally Posted by LagPenguin
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.

OF COURSE, idjit... and that's the point of the derail--that there's a major discrepancy in the rear-wheel numbers off the chassis dynos. Since most of us do'nt have the wherewithal to pull our motors and put them on engine dynos, we have to rely on chassis dyno numbers, and knowing exactly HOW they measure the power and how they calculate it, and how it all relates to the gearing and such, is ESSENTIAL to the whole thing.

So the question still remains.
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Old 08-30-2004, 03:07 PM Tex Arcana is offline  
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i think that looks pretty classy. its not riced up (i dont know what other mods it has probably fart can and HAI), i hope it doesnt get riced up. dont modify it, it looks nice, and doesnt need to be made any louder.

i like the wheels
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Old 08-30-2004, 03:07 PM crshbndct is offline  
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Originally Posted by FlyNavy
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.

Exactly, and you get out a number that represents ENGINE TORQUE, not WHEEL TORQUE. Two completely different things.
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Old 08-30-2004, 03:08 PM demosh is offline  
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Tex Arcana
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Quote:
Originally Posted by FlyNavy
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.

So, what you are saying is that the numbers we see on the dyno display are actually DRIVESHAFT output numbers?
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Old 08-30-2004, 03:08 PM Tex Arcana is offline  
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Quote:
Originally Posted by demosh
Exactly, and you get out a number that represents ENGINE TORQUE, not WHEEL TORQUE. Two completely different things.

So, the numbers posted in my sig are actually ENGINE OUTPUT?? Is that what you are saying?
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Old 08-30-2004, 03:09 PM Tex Arcana is offline  
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SemperFly
 
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Originally Posted by Tex Arcana
OF COURSE, idjit... and that's the point of the derail--that there's a major discrepancy in the rear-wheel numbers off the chassis dynos. Since most of us do'nt have the wherewithal to pull our motors and put them on engine dynos, we have to rely on chassis dyno numbers, and knowing exactly HOW they measure the power and how they calculate it, and how it all relates to the gearing and such, is ESSENTIAL to the whole thing.

So the question still remains.
The next time you go to a dyno run ask the techs there. They will give you the same answer I did. This is why you have to enter in your vehicle's information before you do the pull; it's so the computer can properly calculate the torque numbers without the gears in the equation.
Old 08-30-2004, 03:09 PM SemperFly is offline  
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Old 08-30-2004, 03:10 PM Tex Arcana is offline  
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SemperFly
 
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Quote:
Originally Posted by demosh
Exactly, and you get out a number that represents ENGINE TORQUE, not WHEEL TORQUE. Two completely different things.
Wrong. Because there is still drivetrain loss so those number will never be the same as if you hooked the engine up to an engine dyno and measured at the flywheel. Chassis dynos measure drivetrain loss, period. It's the power at the wheels AS IF you had a 1:1 ratio between the flywheel and the driving wheels.
Old 08-30-2004, 03:11 PM SemperFly is offline  
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Originally Posted by demosh
But I am talking about wheel torque. And those are the numbers at the wheels in first gear in Saab 900s when the engine is at its torque peak. I fail to see any mistakes in my calculations.

you're a dumbass. wheel torque means it's already gone through the gears. you don't multiply a measurement at the wheels by the gear ratio because it's already gone through the gearing to get the wheel measurement.
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Old 08-30-2004, 03:11 PM emericanchaos is offline  
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Tex Arcana
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Quote:
Originally Posted by FlyNavy
The next time you go to a dyno run ask the techs there. They will give you the same answer I did. This is why you have to enter in your vehicle's information before you do the pull; it's so the computer can properly calculate the torque numbers without the gears in the equation.

Some of those techs can't even figure 2+2 without a calculator... they're nothing but a bunch of wrench monkies, with a tad less intelligence.

Fuck this, I'm gonna find out from the source. Watch for a dyno thread in the near future.
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Old 08-30-2004, 03:11 PM Tex Arcana is offline  
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demosh
 
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Wrong. Because there is still drivetrain loss so those number will never be the same as if you hooked the engine up to an engine dyno and measured at the flywheel. Chassis dynos measure drivetrain loss, period. It's the power at the wheels AS IF you had a 1:1 ratio between the flywheel and the driving wheels.

It gives you engine torque, not taking into account what went into overcoming driveline friction. But it is still a measure of engine torque, which is not the same thing as wheel torque.
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Old 08-30-2004, 03:12 PM demosh is offline  
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Tex Arcana
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Quote:
Originally Posted by emericanchaos
you're a dumbass. wheel torque means it's already gone through the gears. you don't multiply a measurement at the wheels by the gear ratio because it's already gone through the gearing to get the wheel measurement.

And you're an idiot if you think gearing doesn't affect torque.
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Old 08-30-2004, 03:12 PM Tex Arcana is offline  
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SemperFly
 
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Quote:
Originally Posted by Tex Arcana
So, what you are saying is that the numbers we see on the dyno display are actually DRIVESHAFT output numbers?
No, not the driveshaft because there's still more drivetrain loss from the driveshaft to the wheels. Going through the differential, half shafts, and then the wheels themselves requires some of the power the engine is producing to be exerted.

The numbers you see are the numbers that you would put down if there was an exact 1:1 ratio between the flywheel and the driving wheels. Chassis dynos are never exactly spot on; that's impossible. But they're the closest most of us will get and this is why some shops are more trustworthy than others when it comes to power numbers. Some places take more care in making sure their equipment is as accurate as mechanically possible, others don't give a shit.
Old 08-30-2004, 03:13 PM SemperFly is offline  
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SemperFly
 
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Quote:
Originally Posted by Tex Arcana
So, the numbers posted in my sig are actually ENGINE OUTPUT?? Is that what you are saying?
Engine output after drivetrain loss, yes. If you were to put your engine on a dyno it would produce slightly better numbers because the engine is no longer turning a torque converter, transmission, driveshaft, etc etc.
Old 08-30-2004, 03:14 PM SemperFly is offline  
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