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-   -   runtime efficiency? (

dcb 04-20-2010 05:10 PM

runtime efficiency?
I was thinking about a sort of "efficiency" readout, though I'm not sure it makes sense.

i.e. if you input your vehicle weight/cDA/rolling resistance, then (not accounting for hills/wind) a mpguino type device could conceivably:

make a guess at how much work was done/is being done by looking at the change in speed.

compare it to the fuel that was/is used to do that work in that amount of time

print out the percentage of work that was actually done vs what the fuel could have done in a %100 efficient engine/vehicle.

But given the influence of hills/wind (and even deceleration) I'm not entirely sure how useful it is. Also it is a little misleading to factor in the cda, your engine can be at peak efficiency but still the whole package is a dog.

I do think something like this could be useful where you have no bsfc clue, or other variables (like a slipping torque converter) and are trying to optimize your acceleration curve.

I also considered a simplified scheme where it simply looks at the change in speed vs fuel used, and comes up with a number that doesn't map directly to anything but you can still look for a peak value, and focus on how to get the greatest change in speed (regardless of your cda/weight) for the least fuel when accelerating. Except for the completely synthesized units, I think this might be easiest to implement and offer the most realistic value. But without CDA, your peak will be a speed dependant moving target.

Any of this make sense? Am I missing something obvious?

nickdigger 04-20-2010 05:51 PM

i've got a simpler "efficiency" number in mine. Multiply mpg * mph, and you sort of figure out what the ideal value is, and try to keep it as high as possible while driving. It basically tells your economy in terms of gas and time, which to me paints a more complete picture than just gas economy. (Time "is" money, after all). Finding your max FE is neat and all, but not very practical if it means you're stuck at 32mph in 5th gear.

It's not a physics equation like you're suggesting, but i'm just tossing it out there.

dcb 04-20-2010 06:20 PM

Lol, no thanks :) FE isn't neat, it is IT.

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