Highway Cruising RPM and Gas Mileage
06-04-2010, 03:39 PM
#11
Originally Posted by urBan_dK,Jun 4 2010, 04:27 PM
I can tell you from my experience that coasting in gear will actually show a higher MPG (as much as 150 MPG from my experience) because the fuel is actually shut off when coasting in gear. If you are coasting in neutral, it uses exactly as much fuel as idling in order to keep the engine running.
Still, coasting in neutral is a better way to go for fuel economy because coasting in gear will decrease your speed much quicker due to the engine braking.
Still, coasting in neutral is a better way to go for fuel economy because coasting in gear will decrease your speed much quicker due to the engine braking.
Originally Posted by Disgustipated
Oh, one more thing I forgot to mention: don't ever put the car in neutral while it's moving. Driving in neutral in the S just wastes gas and messes with the ECU, also causing that "herky-jerky" engine rocking that occurs sometimes when starting in first after coming to a stop. I'll find the links if anyone needs them, but basically the ECU gets confused when the car is in neutral but still moving and it screws up the way it injects fuel.
Anyways, if you're in neutral, it has to inject fuel to maintain idle, whereas if you're coasting in gear, foot off the gas, it isn't injecting any fuel at all. You could be coasting at 7k RPM and as long as your foot is off the gas, it's not using any gas. Also, moving in neutral is more dangerous because you have no power/ability to accelerate and since the transmission isn't stopping you at all, it wears down your brakes faster and decreases stopping power.)
Anyways, if you're in neutral, it has to inject fuel to maintain idle, whereas if you're coasting in gear, foot off the gas, it isn't injecting any fuel at all. You could be coasting at 7k RPM and as long as your foot is off the gas, it's not using any gas. Also, moving in neutral is more dangerous because you have no power/ability to accelerate and since the transmission isn't stopping you at all, it wears down your brakes faster and decreases stopping power.)
I think the only time coasting in neutral MIGHT be acceptable is when coasting down a hill that is steep, but not steep enough to sustain/increase your speed while coasting in gear with no throttle (i.e. the engine's high compression is causing engine braking). You'd save more fuel coasting in neutral rather than continously giving it light throttle. BUT it'd also decrease your stopping power/ability to maneuver in case of an emergency so is it really worth it? That's a pretty big penalty and safety risk. I guess it depends on the amount of traffic around you.
For example, there's a big four lane part of the 60 freeway near me that you can coast down in neutral for about 1.5-2.0 minutes straight, but if you try to do it in gear/with no throttle, you have to keep giving it gas due to engine braking. However depending on the time of day there can be a huge amount of traffic on it. So what's the best thing to do? Maximize fuel economy at the risk of safety? If you have to suddenly switch lanes because someone stomps on their brakes/crashes in front of you but you're in neutral with no power to accelerate and change lanes + full stopping power is dependent on brakes alone, it could screw you over. Seems like either one is a valid choice.
Maybe I'm being overly cautious about the whole thing.
06-04-2010, 05:15 PM
#12
I've posted a lot on this topic in the past. I used to hypermile my Accord for fun.
Anyway, to make a long story short, the best mileage will be achieved at the lowest possible speed in the highest possible gear. In other words, roughly 35 MPH in sixth gear for our cars. Anything over that and you're "wasting" gas.
Engines get the best mileage at the widest throttle openings pared with the lowest RPMs. Cars get the best mileage in the lowest speed you can manage in their highest gear, mostly due to wind resistance, but also because lugging the engine allows you to use a wider throttle opening.
Just because 5K "feels" better than 3K doesn't mean you're using less gas. And just because your throttle opening is less doesn't mean you're using less gas, either.
Anyway, to make a long story short, the best mileage will be achieved at the lowest possible speed in the highest possible gear. In other words, roughly 35 MPH in sixth gear for our cars. Anything over that and you're "wasting" gas.
Engines get the best mileage at the widest throttle openings pared with the lowest RPMs. Cars get the best mileage in the lowest speed you can manage in their highest gear, mostly due to wind resistance, but also because lugging the engine allows you to use a wider throttle opening.
Just because 5K "feels" better than 3K doesn't mean you're using less gas. And just because your throttle opening is less doesn't mean you're using less gas, either.
06-05-2010, 04:10 AM
#13
Registered User
Join Date: Oct 2004
Posts: 181
Likes: 0
Received 0 Likes
on
0 Posts
I concur with thomsbrain.
The first law of thermodynamics applies: energy or momentum can neither be created nor destroyed. Granted, the question is of efficiency, however it would only be a minimal range all the sweetspots a well engineered car could spin more to get more power to the ground without less energy.
More important is aero. The drag on the car is the square of the speed. This would factor into the equation far more than engine/gearing/drive train sweet spot. Think about all the muscle cars with 500 bhp. How many of the really can reach 150 mph?
In the biking world, the US and EU have certain measures of noise and mpg. Almost every manufacturer bike builds a "dip" into throttle response to maximise this rating (which created an industry for jetting carbs/flashing.) Cars are similarly engineered to maximise required numbers.
The first law of thermodynamics applies: energy or momentum can neither be created nor destroyed. Granted, the question is of efficiency, however it would only be a minimal range all the sweetspots a well engineered car could spin more to get more power to the ground without less energy.
More important is aero. The drag on the car is the square of the speed. This would factor into the equation far more than engine/gearing/drive train sweet spot. Think about all the muscle cars with 500 bhp. How many of the really can reach 150 mph?
In the biking world, the US and EU have certain measures of noise and mpg. Almost every manufacturer bike builds a "dip" into throttle response to maximise this rating (which created an industry for jetting carbs/flashing.) Cars are similarly engineered to maximise required numbers.
06-05-2010, 04:56 AM
#14
Regarding "sweet spots" and the notion that the engine is "most efficient" at its torque peak, you have to consider that maximum engine efficiency is going to be at very high torque output levels. Rule of thumb is that piston internal combustion engines have maximum efficiency at 75% power (whereas turbines have max efficiency at 100%).
BUT, during cruise operation in your S2000, the power setting is WAY WAY WAY less than peak power. It's at more like 5-10%. At that low power, internal engine losses from spinning at higher than necessary rpm are going to put a hurting on fuel economy. You will maximize fuel economy by running in the tallest gear you can at low rpm with a wider-open throttle than you will running higher rpm with a smaller throttle opening. This minimizes engine frictional, valvetrain, and pumping losses, and allows the engine to operate at higher torque, giving better specific consumption.
It 'feels like it's working harder" at lower rpm in a taller gear because it is having to provide more torque than it would at the same speed in a lower gear, revving higher. But it's more efficient when "working harder", and you will get greater fuel mileage despite having to give it more throttle.
Regarding anecdotal stories of cars getting better mileage at 80 than at 65, utter b.s... A car that gets better mileage at 80 than at 65 in the same gear has something going seriously wrong with its a/f mixture at 65.
BUT, during cruise operation in your S2000, the power setting is WAY WAY WAY less than peak power. It's at more like 5-10%. At that low power, internal engine losses from spinning at higher than necessary rpm are going to put a hurting on fuel economy. You will maximize fuel economy by running in the tallest gear you can at low rpm with a wider-open throttle than you will running higher rpm with a smaller throttle opening. This minimizes engine frictional, valvetrain, and pumping losses, and allows the engine to operate at higher torque, giving better specific consumption.
It 'feels like it's working harder" at lower rpm in a taller gear because it is having to provide more torque than it would at the same speed in a lower gear, revving higher. But it's more efficient when "working harder", and you will get greater fuel mileage despite having to give it more throttle.
Regarding anecdotal stories of cars getting better mileage at 80 than at 65, utter b.s... A car that gets better mileage at 80 than at 65 in the same gear has something going seriously wrong with its a/f mixture at 65.
06-05-2010, 09:56 AM
#15
Registered User
Join Date: Jan 2009
Location: Long Island City, NY
Posts: 1,212
Likes: 0
Received 0 Likes
on
0 Posts
i'm satisfied with my 20/25 city/highway MPG
but for those who aren't
here, these guys have been doing it for years.
http://www.hypermilingforum.com/
http://www.hypermiling.com/
http://en.wikipedia.org/wiki/Fuel_economy-...izing_behaviors
but for those who aren't
here, these guys have been doing it for years.
http://www.hypermilingforum.com/
http://www.hypermiling.com/
http://en.wikipedia.org/wiki/Fuel_economy-...izing_behaviors
06-05-2010, 12:08 PM
#16
Originally Posted by ZDan,Jun 5 2010, 05:56 AM
Regarding "sweet spots" and the notion that the engine is "most efficient" at its torque peak, you have to consider that maximum engine efficiency is going to be at very high torque output levels. Rule of thumb is that piston internal combustion engines have maximum efficiency at 75% power (whereas turbines have max efficiency at 100%).
BUT, during cruise operation in your S2000, the power setting is WAY WAY WAY less than peak power. It's at more like 5-10%. At that low power, internal engine losses from spinning at higher than necessary rpm are going to put a hurting on fuel economy. You will maximize fuel economy by running in the tallest gear you can at low rpm with a wider-open throttle than you will running higher rpm with a smaller throttle opening. This minimizes engine frictional, valvetrain, and pumping losses, and allows the engine to operate at higher torque, giving better specific consumption.
It 'feels like it's working harder" at lower rpm in a taller gear because it is having to provide more torque than it would at the same speed in a lower gear, revving higher. But it's more efficient when "working harder", and you will get greater fuel mileage despite having to give it more throttle.
Regarding anecdotal stories of cars getting better mileage at 80 than at 65, utter b.s... A car that gets better mileage at 80 than at 65 in the same gear has something going seriously wrong with its a/f mixture at 65.
BUT, during cruise operation in your S2000, the power setting is WAY WAY WAY less than peak power. It's at more like 5-10%. At that low power, internal engine losses from spinning at higher than necessary rpm are going to put a hurting on fuel economy. You will maximize fuel economy by running in the tallest gear you can at low rpm with a wider-open throttle than you will running higher rpm with a smaller throttle opening. This minimizes engine frictional, valvetrain, and pumping losses, and allows the engine to operate at higher torque, giving better specific consumption.
It 'feels like it's working harder" at lower rpm in a taller gear because it is having to provide more torque than it would at the same speed in a lower gear, revving higher. But it's more efficient when "working harder", and you will get greater fuel mileage despite having to give it more throttle.
Regarding anecdotal stories of cars getting better mileage at 80 than at 65, utter b.s... A car that gets better mileage at 80 than at 65 in the same gear has something going seriously wrong with its a/f mixture at 65.
Thread
Thread Starter
Forum
Replies
Last Post
SimbaDogg
California - Southern California S2000 Owners
54
09-11-2007 09:15 AM
Special_K_828
Southern Ontario S2000 Owners
18
01-06-2003 12:46 PM