Hey, all you cleaver dicks.

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sr2, Nov 22, 9:41pm
When comparing the energy consumed in10 seconds with the energy consumed in 20 seconds to achieve the same goal, I would suggest that time (as a variable) was of the utmost relevance.
crzyhrse, Nov 23, 8:11am
It's not. That would only be useful for comparing the rate at which work is done - not the energy used in doing the work. The energy needed to do the work is identical.
crzyhrse, Nov 23, 8:22am
I'd like to see an argument against this which is the fundamental essential of this discussion.

When is work ?
crzyhrse, Nov 23, 8:54pm
No! Can't do it, eh.
clark20, Nov 23, 9:26pm
The engine is more efficient when you achieve the highest compression without detonation, ie like on open throttle, that's how the cylinder deactivation cars work. Less cylinders working at a higher effiiency.
moosie_21, Nov 24, 4:43pm
M1A1 Abrams, uses 2 1/2 gallons per mile (9 litres per 1.6 km's) @ 25mph (37 kmh). Hate to see it's fuel usage in full combat mode, screaming to a top speed of just over 100 kmh. It takes A LOT to haul 60 tons of metal arse.
bagal, Nov 26, 9:15pm
Interesting discussion, not sure what the consensus is. However if f = m x a and w = f x d, ( and work is essentially fuel used) then the fuel used is same in both cases. However the slower accelerating vehicle has travelled further therefore fuel used in l/100km will be lower.
crzyhrse, Nov 29, 9:46am
with 'there' being 60mph, which is impossible to answer due to the unknown fuel efficiency of the engines at the corresponding load and rpm. That also impacts on your L/100km fuel economy claim.
the-lada-dude, Dec 1, 12:19pm
look everybody, as CRZYHRSE said there are too many variables, but these are the variables that make the question interesting and frustrating as well. theres no use fronting up with simple equations that IMO wont cut the mustard. i suspect the type of equation you need is one that gives you the trajectoryof a bullet or similar, i dont know, but sure as hell the amount of energy used wont be the same.
and i'm sure the result will aplly to 99+/-% of all vehicles.
smac, Dec 1, 12:44pm
The amount of energy used is not the same, no, because as discussed above the efficiency of the engine at the different speeds is unknown.

However the work done in both cases will be the same :P
thejazzpianoma, Nov 21, 5:42pm
As crzyhrse eluded to its not straight foward at all and it will depend a lot on the vehicles being tested. Especially as you have chosen the two rates of acceleration that you have.

Many lower powered cars will be using almost full throttle to achieve the 10 seconds and while smooth but brisk acceleration is often the most economical the best efficiency is rarely achieved near full throttle.

There is the matter of a lack of pumping losses with the wider throttle opening that works in its favor, manual vs auto as to accelerate fast in a manual you have to hop on and off the gas quickly and various other factors.But before we even go there you have to consider the question again.

You say which car uses more fuel getting to a speed as opposed to covering a distance. That's a tricky one as the slower accelerating car will cover a greater distance before reaching the same speed.

There is an australian website I think you would really enjoy which tests a lot of this stuff and goes into detail (but keeps it easy to read) on the pros and cons of fast vs slow acceleration etc. They even have some electronic kits you can make which allow you to test/measure for yourself.

Great thread!
richardmayes, Nov 22, 10:40am
And re the original question -

Is your engine [more efficient], when it's making 200 horsepower, than it is when it's making 40 horsepower!

Or [less efficient]!

Or [equally as efficient]!

Or [we don't know]!

Edit: I ask this because unless you know, it's impossible to say whether accelerating hard, so that you get up to your steady low-throttle cruise speed in a shorter time, is using more or less gas overall.