# Gear an torque In/Out

Discussion in 'Diesel Engines' started by Lee01, Aug 2, 2013.

1. Joined: May 2012
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### Lee01Junior Member

Hello, I'd like to understand something about torque and gear,
for the selection of a drive model

I am sure that Rpm speed is divided by reduction ratio, for example 3300 rpm at crank will output 2000rpm at the propeller:

what about Torque? Is it divided by 1,55 also or multiplied? and horsepower?

Thanks

2. Joined: Aug 2002
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### gonzoSenior Member

If the RPM are reduced, the torque is multiplied by the same ratio. There are frictional losses that depend on gear design, but you can estimate roughly at about 3%.

3. Joined: May 2012
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### Lee01Junior Member

simple question simple answer =) thank you!
so power in hp will be divided also? or it remain the same (less3%) ?

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### DCockeySenior Member

Power remains the same less any losses (frictional, oil churning, etc).

5. Joined: May 2012
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Location: Italy

### Lee01Junior Member

fine so the gear only trade rpm in torque, and the power remain the same more or less, I also found this torque calculator based on power * speed
http://www.wentec.com/unipower/calculators/power_torque.asp
is it right for non-electrical engines where performance chart are not linear?

also why permormance charts are not linear? power and fuel use aren't proportional with rpm of the engine?

6. Joined: Oct 2009
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### DCockeySenior Member

Power = Torque X Rotational Speed (with appropriate unit conversion factor)

Torque = Power / Rotational Speed (with appropriate unit conversion factor)

Rotational Speed = Power / Torque (with appropriate unit conversion factor)

The relationships above hold for any rotating system, including Diesel engines, gasoline engines, electric motors, steam engines, windmills, water wheels, steam turbines, gas turbines and squirrel cages.

Torque varies with speed of the engine which is why power is not proportional to the speed of the engine. Fuel use of an engine depends on a number of factors.

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