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Old 01-05-2013, 10:56 PM   #26
Scooby Specialist
Member#: 268354
Join Date: Dec 2010
Chapter/Region: NESIC
Location: Massachusetts
02 WRX 05 LGT
Slow Automatics


Originally Posted by ProfessWRX View Post
Seems like you haven't done a lot of things.

Why don't manual guys slip the clutch on dynos?

How does a dyno calculate torque? Does it use rpm? What happens if the Rpms are not directly connected to the drivetrain rotation?
Lol and you know everything I understand what you are saying, and it applies 100% if you are using a road dyno software. If you're measuring RPM accel vs. time NOT roll speed accel vs. time, slipping the clutch would net big numbers. Usually, like Airboy says, without a rpm pickup, you use a function called "calculate from roll speed" to estimate RPMs. If you're simply measuring torque output without a direct RPM signal to the dyno, slipping the clutch would just drop power, and kill your clutch. I'm not really sure where you're going with this.

I can tell you though, the auto has much more torque in the stall speed range than a manual does, whether you want to beleive it or not.
Originally Posted by Airboy View Post
The Torque curve, as plotted against engine RPM, is not accurate in the sense that the engine is not actually at the RPM indicated on the chart but I wouldn't go as far as "artificially inflating..." That RPM scale is calculated from the roller speed. As soon as you step on the gas, the engine will speed up to the stall speed and the wheels has to "catch up". The calculated RPM will be less than the actual engine speed.

That being said, the torque curve, as shown, does give an indication of the acceleration that you would feel. Imagine if you were blindfolded and didn't know the car had an automatic, would it feel like a lot of "low end" torque?

I made some plots and stuff that covers this:
More or less this is what I was trying to get at. You're just much better at articulating it. I would like to see torque output plotted vs. time, taking RPM out of the equation, and see if it would change the shape of the graph.
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BlazeRex is offline   Reply With Quote