lots of threads banging on about fuel economy this , diesel that. two identical vehicles, road ,climatic , driver,etc all identical ( you get the picture ) one of the vehicles accelerates to 60 mph ( where using real measurement here ) in 10 seconds. the other gets to 60 mph in 20 seconds. ok ! every dumb dick and his dog can understand that one, BUT, which vehicle uses the most fuel getting there ! what's the answer, .mmmm. i'm not sure, but i think the slow one uses more fuel .
ginga4lyfe,
Nov 21, 5:03pm
I reackon ur right, it takes alot more fuel to get a car moving than to keep it at speed, so the longer you take to get to speed the more fuel you would be needlessly using , BUT this would only work/be true with in reasonable terms ( ie no good valve bouncing a car to get to speed )
rob_man,
Nov 21, 5:07pm
Ain't puttin' no cleaver near my dick. Anyhoo. I'd say the one which isn't working so hard would be more economical if the acceleration times were identical but would lose that gain if you halved the acceleration time. Are we clear! Confused! I am.
gunhand,
Nov 21, 5:09pm
They both may well use the same amount.
the-lada-dude,
Nov 21, 5:20pm
good one rob-man, good answers, i honestly thought this thread would get kicked to the gutter
smac,
Nov 21, 5:24pm
Nah it's a fair question. All to often somebody waves a number (eg fuel economy) and that gets used as the be all and end. Hell if I drove a 1.3 econobox over the same route as wifie, but she was in a 3.5lt V6, I'd still use more gas. The focus should be on production costs and recyclable materialsif they really wanna get somewhere.
crzyhrse,
Nov 21, 5:24pm
It depends on which one is the most energy (fuel) efficient at the engine speeds it takes to do it because while the rate of work is higher for the faster accelerating vehicle, the total work done is exactly the same as it does the higher rate of work in a shorter time. F= m x a and E = F x d / t
hutchk,
Nov 21, 5:28pm
I started to think about it, then realised I don't care.
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 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.
More throttle generally means more fuel. Add things about efficiency, cam profiles, spark and fuel maps transition from cruising to acceleration here.
Mostly to do with the ecu suddenly sees X% throttle and map reading (some amount)kPa then the 3d tables intersect somewhere based on RPM. More throttle, more spark advance, more acceleration enrichment generally. On a carb car it just sees lower vacuum = more fuel.
socram,
Nov 21, 6:47pm
According to the boffins at Land Rover, accelerating to cruising speed quickly is more ceconomical. If you accelerate briskly, it is fine, but obviously if you are going to red line it in each gear.
The quicker you get in the higher gear the better.Economy at the end of the day is being able to have the engine ticking over rather than working, which is why a 1500cc car may be less economical than a 2000cc car as the smaller car may need to change down, but the larger car may not.
crzyhrse,
Nov 21, 8:40pm
Some of you seem to be missing the stipulation in the first post. IDENTICAL VEHICLES.
crzyhrse,
Nov 21, 8:41pm
"Power or torque" threads are better.
the-lada-dude,
Nov 22, 5:36am
there you go ! good feed back everyone. but CRZYHRSE is right, we must read and try and interperate the question correctly ! i forgot all about pumping losses, but something in the o'l brain must have dismissed them as being too close to call. i personally thought the biggest factor would be wind resistancevtime.
smac,
Nov 22, 5:54am
OK, identical vehicles. The answer is still 'it depends'. Each of the vehicles will be using different throttle settings at different parts of the rev range, so all depends where that engine operates more efficiently. For some vehicles that would be taking the slow route, some it will be the fast.so what vehicle are you talking about!
tigra,
Nov 22, 8:05am
Tend to agree.But on reviewing the behaviour of most other drivers at traffic lights it seems that most have made up their mind that getting uop to speed as quick as possible is best.
the-lada-dude,
Nov 22, 8:14am
what vehicle am i talking about. !.well ok,lets just say your average run of the mill sedan.mmmmm.w- hat about a V W golf
sr2,
Nov 22, 8:36am
Great thread. Draw a graph with MPH on the Y axis and time on the X axis; the area under the graph will be distance covered, in effect work done or fuel used. In the ???perfect theoretical car??? (i.e. no air resistance, linear acceleration, consistent fuel delivery, etc.) the most fuel efficient will be the 0 to 60 in 10 seconds scenario. The answer to the OP??
crzyhrse,
Nov 22, 9:16am
I think that's exactly what I said.
smac,
Nov 22, 9:20am
Indeed.
crzyhrse,
Nov 22, 9:33am
That's a completely different kettle of fish.
crzyhrse,
Nov 22, 9:34am
What I really want to know is why nobody pulled me up on E = f x d / t in post #7.
smac,
Nov 22, 9:38am
'Cause no one read it!
rob_man,
Nov 22, 10:34am
True, we all know e=mc squared.
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