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Old 07-30-2012, 05:55 PM   #12 (permalink)
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GasDwarf - '13 Volkswagen up! EcoFuel CNG
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Originally Posted by LocoJason View Post
the car would actually pay for itself in 3 years vs my previous commuter vehicle. Win-Win.
That's the way to do it.

For many years I had been into performance cars
You're not the only one around here - far from it

I thought "slower is better, right"?
Not necessarily, as you've found out.
Depending on engine management and gearing, there's a speed where the engine won't pull off the good MPGs anymore, or will only do so under very favorable conditions.

If I drop down below 1750 (max torque on the turbo diesel) in steady driving, mileage drops down with it - unless the road is dead flat and I'm coming down from a higher speed.
But a very minor incline will make the fuel consumption jump though.

At highway / high-drag speeds, 1750 rpm in 5th is around 85 kph / 53mph.
Dropping below that, the mileage drops off significantly - like 10-15% less around 80 kph .

The downside of fast rising torque curves, is that you also fall off like a brick when going the other way

I have not tested slower and I still wonder at what speed the aerodynamic drag has reduced enough to offset the lower efficiency of the engine and actually deliver an increase in economy?
For me, at idle in 3rd or 4th !

Drag is so low, the engine can pull it off with record mileage - but the slightest increase in loading will result in bad mileage, even climbing a speedbump can kill the fun.

So that leaves me with aero mods and rolling resistance to focus on...
There's a lot to be gained from modding your driving style as well.

Basically, using only the power you need to get you to the next corner / light / stop sign at appropriate speeds - and not much more.

Are you already using coasting in neutral (or even with the engine off ) ?
GasDwarf's fuel consumption :
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LocoJason (07-30-2012)