Quote:
Originally Posted by PencilGeek
Let me see if I can destroy this myth without starting a flame war. This myth probably wouldn't even exist if more people understood how the power is transmitted from the motor to the wheels. I think this myth continues to propogate -- mostly -- because it sounds like it makes sense on the surface and most people don't understand how power is transmitted. So they blindly accept it, and the myth continues to propogate. So let's see if I can dispell it -- at least for the 20 people who may read this message.
Regardless of torque and RPM, some value of power exists at the flywheel. The flywheel causes the primary shaft of the transmission to spin. The gear on the primary shaft has some number of teeth on it, and meshes with another gear on the secondary shaft that has a different number of teeth on it. This is how you get a gear ratio: 87 teeth on the primary divided by 55 teeth on the secondary equals a 1.58:1 gear ratio (87/55=1.58). Obviously a 1:1 gear ratio has the same exact number of teeth on the primary and secondary shafts.
The drive shaft is connected to the secondary shaft of the transmission. But before getting to the wheels, there is one more conversion to take place: the final drive ratio. The secondary shaft/drive shaft spins a primary gear in the final drive, which in turn causes a secondary gear to spin as well. Once again, divide the number of teeth on the primary shaft with the number of teeth on the secondary shaft, and you get the final drive ratio. In the case of the M3, there are 100 teeth on the primary, and 26 teeth on the secondary giving a 3.8462:1 final drive ratio (100/26=3.8462).
Since both of these gears reduce the motor RPM to wheel/hub RPM, they BOTH act as torque multipliers. It's important to understand that BOTH gears act as torque multipliers: the transmission gear ratio AND final drive ratio act as torque multipliers -- not just the transmission gear ratio. It's easy to calculate the combined torque multiplier, as it's simply the gear-ratio x final-drive-ratio. In this case, 1.58 x 3.8462 = 6.084.
To compensate for the torque multiplier, you simply divide the measured results by the torque multiplier to obtain the actual results. In the case of a 3rd gear run on the M3, divide the measured results by 6.084 to obtain the actual results. If you look at the dyno chart, you will see they did exactly that. You will see '6.084' in the bottom right corner of the dyno chart. That was the torque DIVISOR from the measured results. If it weren't there, you'd be seeing over 2400 horsepower from this motor.
The myth:
Regardless of which dyno you use, you are always getting a torque multiplier because whichever gear you choose is always being run through and multiplied by the final drive ratio. The myth states that you need to run as close to 1:1 as possible -- completely ignoring that a final drive ratio even exists. Well the bad news for people who don't think for themselves: a final drive ratio does exist, and always acts as a torque multiplier itself. Eliminating the torque multiplying effects is as simple as dividing the measured results by this value.
So at least for the 20 people reading this thread, I hope you'll now understand how this works...and why it doesn't matter.
Oh, and for those of you still tempted to say that you need to run in 5th gear (1:1), think again. Your speed limiter would kick in before your dyno run is over...and completely invalidate your results.
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So under ''No Speed Restrictions'' requirements what is the Best Gear to Dyno the M3...?
1)3rd
2)4th
3)5th
4)Any...?
P.S. Stil trying to find out why my car is putting (327 whp With Rpi Scoops,BMC Filter,and ACS Rear Mufflers heheheheh,maybe we should recalculate some factors on the Dyno se we can have percise resaults according to the factory claims)