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Smart quod bastardus
 
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Join Date: Oct 2002
Location: Baltimore, MD, USA
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Quote:
Originally Posted by TurboKraft View Post
Ideally, a 1:1 drive ratio. For a 930 4-sp, 3rd is closer to 1:1 than 4th is.
Why is it so important for a 1 to 1 drive ratio?

I know running a higher gear gives you more time to get load and high boost on the engine, but do not understand the importance of 1 to 1 ratio in the tranny.

Fred

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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 06-13-2013, 01:21 PM
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Quote:
Originally Posted by fredmeister View Post
Why is it so important for a 1 to 1 drive ratio?
Because gear ratio can increase or decrease output torque by a factor of the gear ratio, not accounting for friction losses.

From Wikipedia:
A gear train can be analyzed using the principle of virtual work to show that its torque ratio, which is the ratio of its output torque to its input torque, is equal to the gear ratio, or speed ratio, of the gear train.

This means that the input torque TA applied to the input gear GA and the output torque TB" on the output gear GB are related by the ratio

where R is the gear ratio of the gear train.
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3.3L, K27HFS, Tial 46mm, TurboKraft Intercooler, 964 Cams, Monty Muffler, MS3Pro Evo, M&W Ignition, Zietronix WBO2 Data Logger, Wevo shifter, coupler and motor mounts.
Old 06-14-2013, 11:25 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #22 (permalink)
Smart quod bastardus
 
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Join Date: Oct 2002
Location: Baltimore, MD, USA
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Quote:
Originally Posted by WinRice View Post
Because gear ratio can increase or decrease output torque by a factor of the gear ratio, not accounting for friction losses.

From Wikipedia:
A gear train can be analyzed using the principle of virtual work to show that its torque ratio, which is the ratio of its output torque to its input torque, is equal to the gear ratio, or speed ratio, of the gear train.

This means that the input torque TA applied to the input gear GA and the output torque TB" on the output gear GB are related by the ratio

where R is the gear ratio of the gear train.
Got it now i feel stupid for overlooking this. I was thinking wheel horsepower and mistakenly thought gear ratio has no effect but you are right sir. So I guess the dyno does a conversion based upon the gear ratio you enter and then converts to RWHP. The of course you can back calculate HP at the crank using a good suitable tranny loss number which most people accept 12-15% for the 911.

Thanks
Fred

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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 06-15-2013, 04:41 PM
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