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Fuel Consumption, a bigger or smaller engine

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Old 09-07-2010, 03:47 PM
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TullyK
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Default Fuel Consumption, a bigger or smaller engine

I was thinking about how fuel consumption rockets at wide open throttle, and thought could fuel consumption be reduced by using a slightly more powerful (and higher capacity) engine but then running it at eg. 80%, or whatever figure that will give the same power as what the smaller engine running at WOT. Surely the larger engine would use less fuel because this increase in fuel consumption near full throttle is greater than the increase in power. I was wondering this when thinking could i improve the economy of a 30hp boat by fitting it with a 40hp engine and running it at 75-80% but i suppose it could be applied as easily to RC although one would have to ignore the increase in weight of a bigger engine.

I'd like to hear any thoughts people have on this for both RC engines and larger petrol engines (or diesel) so thanks in advance
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Old 09-07-2010, 04:21 PM
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Default RE: Fuel Consumption, a bigger or smaller engine

It will always take X amount of energy to produce X amount of horsepower,,
the difference is, if you use a larger engine at lower RPMs it will live longer than a smaller engine running wide open all the time to produce the same horsepower
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Old 09-07-2010, 04:32 PM
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Default RE: Fuel Consumption, a bigger or smaller engine

Thanks for the response, how does this account for the drastic increase in inefficiency at higher rpm whereas only a small increase in hp?

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Old 09-07-2010, 05:15 PM
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Default RE: Fuel Consumption, a bigger or smaller engine

Because the closer you get to max horsepower the curve flattens and the less difference you see, engines once they get past Max horsepower start to drop horsepower as RPMs increase,, that is why gearing, or as it pertains to airplanes or Boats, Prop choice is so important, you want to run an engine in it's most eficiant range so you're not just dumping fuel in and not getting a return.
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Old 09-07-2010, 06:59 PM
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Default RE: Fuel Consumption, a bigger or smaller engine


It will always take X amount of energy to produce X amount of horsepower



This right here, you cannot trick the laws of physics, anything else is just black majic.....................
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