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Old 01-05-2015, 02:21 PM   #6 (permalink)
Vekke
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Join Date: Jan 2009
Location: Kitee (Finland)
Posts: 980

Siitin - '98 Seat Cordoba Vario
90 day: 58.56 mpg (US)

VW Lupo 3L --> 2L - '00 VolksWagen Lupo 3L
Diesel
90 day: 104.94 mpg (US)

A8 luxury fuel sipper - '97 Audi A8 1.2 TDI 6 speed manual
90 day: 64.64 mpg (US)

Audi A4B6 Avant Niistäjä - '02 Audi A4b6 1.9tdi 96kW 3L
90 day: 54.57 mpg (US)

Tourekki - '04 VW Touareg 2.5TDI R5 6 speed manual
90 day: 32.98 mpg (US)

A2 1.4TDI - '03 Audi A2 1.4 TDI
90 day: 45.68 mpg (US)
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Quote:
Originally Posted by JRMichler View Post
To help interpret Vekke's graph:

If you need 7.5 hp (5.6 kW) at a particular speed, the best gear ratio is that which has the engine running about 1400 RPM at that speed.

If you need 15 hp (11.2 kW) at a particular speed, the best gear ratio is that which has the engine running about 2000 RPM at that speed.

If you need 60 hp (45 kW), you don't have a choice. You only get that much power at about 4600 RPM. But if you keep the gas pedal on the floor, and change gears to get 3300 RPM, the power drops slightly to about 56 hp and the specific fuel consumption improves from about 250 to 222 g/kWh. That's 13% better (more efficient) use of the fuel.
5,6 kW was correct in my opinion

For the 11,2kW I would say the optimal rpm is that 1800 RPM? but in general you have also take into account how many gear you will have at speeds you are using the most. I am trying to optimise my gears for highway use meaning 62-100 MPH cruising speeds. That means tallest gear ratios are always better.

For 45kW I have plenty of options in my car as there will be 89 kW+ available in the first stage. But with stock engine BSFC map that this is there is not much choices.
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