To shift or not to shift...
10-03-2006, 05:38 AM
#1
Launching!
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To shift or not to shift... Im not sure if this is in the right section but Im wondering why do automatic transmissions produce lower dyno numbers?
I understand the basic concept that more power is lost through the drive train but what exactly does that mean ?
In theory, with all other variables being the same, same track, same driver, same car, same conditions, etc, a a4 will produce approx. the same results at the track as the m6 or m5? For example a th400 vs a t56 ?
I understand the basic concept that more power is lost through the drive train but what exactly does that mean ?
In theory, with all other variables being the same, same track, same driver, same car, same conditions, etc, a a4 will produce approx. the same results at the track as the m6 or m5? For example a th400 vs a t56 ?
10-03-2006, 06:35 AM
#2
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Well the biggest thing is to understand what and how an auto tranny works. A torque converter multiplies torque, because the input shaft spinns faster than the output shaft. This is a visous coupling. Once lockup occurs it is more efficent. But more effort is required to rotate an auto tranny.
And actually results will not be the same. This is for many reasons such as internal gear ratio, but some is due to drivetrain loss.
Typically a M6 Ls1 is capable of 106-109mph traps. An auto will more likely be 102-105mph for the same weight car.
ET's are often similar because auto's are very easy to launch. And with a few mods you can really get cosistantly blinding 60' times.
And actually results will not be the same. This is for many reasons such as internal gear ratio, but some is due to drivetrain loss.
Typically a M6 Ls1 is capable of 106-109mph traps. An auto will more likely be 102-105mph for the same weight car.
ET's are often similar because auto's are very easy to launch. And with a few mods you can really get cosistantly blinding 60' times.
10-03-2006, 09:43 AM
#3
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If we were to change our dyno's system, from measuring engine HP Vs RPM to drive wheel's "force" at the rollers Vs MPH, we would see a better representation of our performance mods, especially high stall speed autos or rear gear changes. We have made some high stall auto drivers very happy when we could show them such graphs, due to the auto's stall speed's ability to multiply torque to the wheels resulting in more "force" being applied to the rollers, or ground. Another way of saying this, anytime we do something to raise the engine's RPM higher so it is averaging more HP due to being closer to its peak HP, we will see more pulling power at the wheels. Usually this gain will offset the extra losses due to less drive train efficiancy. Again, we have to think about what we are accomplishing per MPH, not RPM.