View Single Post
      12-04-2013, 04:51 PM   #12
Boss330
Major General
Boss330's Avatar
No_Country
1712
Rep
5,108
Posts

Drives: BMW
Join Date: Mar 2012
Location: Earth

iTrader: (0)

Quote:
Originally Posted by tom @ eas View Post
Great question.

On F10 M5, we have to use 4th since we end up reaching the top speed limiter before redline on 5th. Numbers are relatively similar in both gears (even on M3).
Thinking more about it and checking online, it seems there is a lot of confusion on the subject. But this makes sense to me:

Quote:
Anyway, the main issue here is that in order to properly measure/estimate power, any dyno needs to look at the rate of acceleration of the wheels (or hubs), the force being overcome by the wheels, and finally a clean engine RPM reading. The RPM reading is what most people seem to be missing in their assumptions. As long as the dyno knows the wheel speed AND the engine RPM, it can calculate the gearing that got it there. Now as long as these values are recorded properly, the dyno should not show any significant power differences between gears (aside from external factors). Just because in 2nd gear, the torque actually applied to the wheels is greater than in 3rd or 4th gear, doesn't mean the dyno will read higher. It simply looks at the wheel speed versus engine RPM, calculates the correct gearing and displays the correct power output.
So, forget my gearing question... If dyno'd correctly with correct RPM to the dyno, the results should also be correct, since the dyno "corrects" for both the final drive ratio and gear ratio. I.e, the dyno understand the total ratio and the engine does the exact same work regardless of what gir you're in. Just like if you changed the final drive ratio, the engine wouldn't make less power. But it might be able to accelerate the car faster or have a lower cruise rpm. But the engine still makes the exact same amount of HP! As long as the dyno takes engine RPM into the calculation, results shouldn't vary between different gears (apart from variations in frictional losses between different gears)

Last edited by Boss330; 12-04-2013 at 04:58 PM..
Appreciate 0