oh....
sorry.........
I thought this was the "FUCK" thread.
...fuck gas prices, they suck. anyway you look at it.
Gasoline usage for BM
I can't get the person at sunoco I want on the phone, but generally yes, but not always.mdmf007 wrote:Octane rating only refers to the ability to spontaneously detonate. It gives no more power over lower octane ratings.
Where you do get more power in higher octane ratings is in engines that need it, these engines run at a higher compression rate. A lower octane rating run in a higher compresion engine, will knock, or pop the heads off. The fuel is detonating on its own before the piston is at TDC (Top Dead Center) in effect trying to shove it back down, before its all the way up. Higher octane resists this urge and allows the spark to blow it off.
a higher octane rating in an average engine makes no difference in power or efficiency
Wind resistance is a function of the square. resistance at 100 MPH isnt simply twice that of 50MPH. So i would have to believe that there is a happy medium.
later
Premium fuel often contains higher energy content as well as higher octane numbers and then there is MON and so on.
Engines usually derive 30% energy at best from a gallon of gas, so it is not that important.
I will try to get more specific info if anyone cares.
Many luxury cars and others are designed for premium for efficiency.
Wiki mentions that driver habits and a full load can create a need for higher octane that would not otherwise exist.
Again, if it saves you money, use it.
But it may be only on a trip to burning man that some need it.
There is a happy medium, but it is not the same for all cars.
They started trying to sell the 'slow is always better' myth with the 55 mph limit.
It probably dates back to trying to dissuade teenagers from driving fast in the twenties.
When they couldn't back it up, suddenly it was always a safety issue.
They never backed that one up either.
Some vehicles do not behave in a linear way as speeds increase.
My experience with a van with a 318 and a 4-speed was that I hit a wall at 85 mph and never could exceed that speed.
My large ford doesn't even taper off until 120 and then it is a gradual reduction in acceleration. I get about 25 mpg at 80 mph.
Both of these vehicles had better mileage with premium fuel.
The van was stock.
I achieved 26 mpg with it at 65 mph in the hills once with overdrive.
My wagon is a relatively high drag design.
I might mention that blocking the grille usually improves drag.
Many cars that were measured with better fuel economy with ac, were in fact doing better due to lower drag caused by the ac components restricting the grille.
As simple a thing as changing your gear ratio can change your mileage at highway speeds.
I have larger tires on my wagon which gears the car taller.
This could lower or raise the speed of the peak mileage speed.
There are many things involved.
Reducing drag is always a plus, no matter what.
You're always funny, Pinemom!
Lowered cars almost always have lower drag.
This is not cheap to do properly and there are consequences.
I will probably lower my wagon an inch at the front with special springs.
But trucks are very often artificially raised to get that 'sport ugly vehicle' stance.
They would benefit dramatically and handling is improved too.
Some cars are jacked up to meet bumper height specs.
An air dam is relatively easy though.
Mine will probably be ugly and a fairly poor design so I can destroy and replace as needed.
Lowered cars almost always have lower drag.
This is not cheap to do properly and there are consequences.
I will probably lower my wagon an inch at the front with special springs.
But trucks are very often artificially raised to get that 'sport ugly vehicle' stance.
They would benefit dramatically and handling is improved too.
Some cars are jacked up to meet bumper height specs.
An air dam is relatively easy though.
Mine will probably be ugly and a fairly poor design so I can destroy and replace as needed.
-
Captain Goddammit
- Posts: 8589
- Joined: Sat Sep 06, 2003 9:34 am
- Burning Since: 2000
- Camp Name: First Camp
- Location: Seattle, WA
Incorrect. Premium fuel does not have more energy content. If your vehicle runs better on it, either it isn't tuned properly (often too much spark advance) or has a too high compression for low-octane or is being operated in a way that maximizes knocking (heavy load, high temp, etc.) And MON, Motor Octane Number, is simply a different test, using an engine with more variable load and tuning parameters, as opposed to Research Octane Number, obtained by a test engine with no variables except compression ratio. The octane number you see on the pump is the average of RON (Research Octane Number) and MON.gyre wrote:I can't get the person at sunoco I want on the phone, but generally yes, but not always.
Premium fuel often contains higher energy content as well as higher octane numbers and then there is MON and so on.
They have engines with higher compression ratios mostly to make more power.gyre wrote:Many luxury cars and others are designed for premium for efficiency.
Wiki mentions that driver habits and a full load can create a need for higher octane that would not otherwise exist.
The condition that is most apt to knocking is the combination of heavy throttle, low rpm, and high load. So of course a heavy load will amplify it.
It is, MPG-wise. Like mdmf007 and I have already said, aerodynamic drag increases exponentially with speed. There is no getting around the fact that it takes 4x the power to go twice as fast due to aerodynamic drag. There are other things like rolling resistance, etc. but at speeds over 50-ish to maybe 60-ish, aero drag becomes the main thing you're fighting.gyre wrote:They started trying to sell the 'slow is always better' myth with the 55 mph limit.
Your engine does not run THAT much more efficiently at high RPM that your MPG will increase when driving at speeds over 60 or 70 where you are fighting WAY more aero drag. And you could always shift to a lower gear.
How fast your vehicle is capable of going at full power has zero to do with what it's most efficient cruise condition is. Full speed is about the worst for efficiency.
Oh, and larger tires are a tradeoff too. If they are heavier, you will lose efficiency. The most important and effective place in an entire vehicle to remove weight is the wheels, by far. A pound of weight off the wheels and/or tires is MUCH more effective than a pound of weight off the body or chassis.
Smaller, lighter wheels will return the highest MPG.
GreyCoyote: "At this rate it wont be long before he is Admiral Fukkit."
Since none of this is becoming succinct, I'll sum it up.
Do what improves your car.
It does help to know what is going on, but check your own results.
On the aero drag question, I think a good analogy is speaker efficency.
I use very efficient speakers.
If I increase power to 100 watts, I get a certain level.
If you start with less efficient speakers, the power consumption is not too different to reach the same level at first.
As the level goes up, the gap becomes larger and larger, rapidly becoming enormous.
The drag factor you are fixed on, is the reason that cars are all different in their ideal use, rather than similar.
A streamlined car will become more dramatic in it's differences as drag increases.
A poor design will become more dramatic in the negative, for the same reason.
I also said it's not relevant.
I could probably find out exactly what is available, but I see that the sae is still debating energy content vs derived energy from fuel.
I could find out eventually, but there is much disagreement about what mixtures produce energy.
You might compare it to the measuring of food by burning it.
It sometimes has little relevance to derived energy in a digestive system.
Perfectly valid data....for a furnace.
I can't wait to get my daily driver to require premium either by advance or raising the compression to where the engine was designed to run and probably both. As long as more efficiency is obtained, it seems like a good thing.
An unusual engine design in the usa, italian car.
I found it too noisy, but I did not in fact have another gear to shift into.
But the mileage was higher.
I was shocked too.
The power curves were in the owner's manual.
Interestingly, the gov website touts the 'slow driving saves gas' still and mentions air drag, but it's own chart of the mythical "regular car" shows an increase in mileage as speed increases and a long plateau before trailing down.
It is all very simple to explain. It's much more complicated than air drag.
A high drag car with a small inefficient engine will probably get better gas mileage at slow speeds.
But what if you don't have a piece of crap?
How about a truck with a very efficient but large engine?
Drag will be a factor quickly, so the gearing must be set for the best load on the engine without so much drag yet. Easy right?
How about a small, very slippery car with a tiny efficient engine?
Until drag overloads the engine, the higher the speed, the better.
You cannot use an engine that maxes at 55 mph if you want a margin for emergencies and running ac.
Such a car will probably use more fuel to run ac at 60 mph than it does to cruise. Stress a car engine too much and it wears too quickly.
See how easy it is to design a car and get it right?
Put a really efficient engine in a truck and you have no power when loaded.
Running empty, the best speed may be high.
Loaded, it could reach peak efficiency at 45 mph.
i know someone with a 660 cubic inch engine in a full size van.
He can tow a 45 foot trailer, two cars, pit crew, 8000 pounds of tools and parts uphill with the ac running in the mountains.
It probably takes more fuel to idle it at 40 mph than it does to propel it.
I know someone with an audi S6 wagon.
It can achieve 170 mph, so it is much more slippery than it looks.
With aero that good, where do you think the mileage peaks?
I don't know, but I'm guessing faster than a Crown Victoria.
The way drag increases is precisely why every car will vary so much in it's ideal speed for mileage.
A bad design gets worse really quickly.
A good design gets worse equally quickly (if we ignore variables) so the good design still ends up with far, far less drag and the difference gets bigger as speed increases.
Still more complex are variables.
My ford stops flowing air over the grille past 40 mph. If the fan isn't on, it starts overheating past 45 mph.
Let's not even get into beneficial turbulence to reduce separation or the really tricky stuff.
Full speed?
The only thing I've had, that had best mileage at high speed was the fiat with a 5000 rpm efficiency peak.
That engine would run to 10000 rpm though.
The big engine produces 300 flbs of torque off idle.
It has tall gearing.
Driving it at 40 mph I'm just wasting heat.
3600 pounds, 500 hp/500flbs and a slippery body (and 11.5 to 1 compression) and 25 mpg.
I think 100 mph would be the mileage peak.
I'm not saying this is normal.
It does show the variables.
That is not top speed.
Top speed is theoretically 180 mph with current gearing.
I think I could do better, just not interested, unless I get the chance to take it to europe.
Honestly, when you hit 100 in seconds, I'm happy.
The car hasn't been over 150 and I have no plans to do so, even on a track.
125 is a very comfortable, stable cruising speed for it.
They won't let you drive like that here for long distances though.
Please explain what is magical about any speed?
If engine loading doesn't factor into it, then why would any speed be selected over another?
Why don't you go to the burn at 15 mph?
Why don't planes go 55 mph?
The answer is efficiency.
And I remind you that cars and trucks are not theory and they don't all have an identical reaction to drag as speeds increase.
My wagon is great but it has serious drag issues, that climb radically with speed.
The bigger ford was designed for daytona and is much better than it looks.
You're getting into a very complex issue.
All that matters is what you have and can you make it better.
I already addressed narrow tires.
Certain models do have far less drag.
They tend to be slippery, hard surfaced and flexible where they shouldn't be.
I fear I will need to stop one day. Hard.
I use alloy wheels already.
The only option I would use is softer high performance tires in a narrower configuration to compensate for the loss of grip.
What I hear from prius owners is that once they dumped the tires, it was a decent car.
I mentioned the tire option as an easy approach for small gearing changes.
How many motel stops will you have to pay for on a 2500 mile drive if you drive at 15 mph? Will it cost more than you save in gas?
How much time will you save if you drive 15 mph over your ideal, presuming you find that out, again over 2500 miles?
(I used to ride a bike enough to think about these things once.)
Is x mpg worth x hours of your trip time? ( and exhaustion?)
Don't forget tailwinds.
If aero is the only factor, then the existing math for planes should work just fine on cars.
Try it.
There is a great deal of research already done on these issues.
High speed vs low speed driving in germany has been debated for years.
High speed referring to over 120 mph+
It was found that between the two major types of pollution, one increased dramatically.
Further research and better methodology found that the other type dropped equally.
Measurements were for time and not distance, so once that was factored in, it was found that as specific engine efficiency increased (not referring to mileage here) pollution was better managed.
The per mile pollution from a high speed car, even if it was burning more fuel, was equivalent to a car going 62 mph.
You may have a car that peaks at only 40 mph.
Tell me why 40 mph and not 55 mph or 70 mph or 15 mph?
There is no air 'barrier' at a certain speed, unless maybe you have a very fast car. (mach 1)
There is a reason they spend huge sums of money on wind tunnels with rolling beds.
The road is part of the aerodynamics.
A car is much harder to understand than a plane in terms of the effect of air.
We aren't doing basic research.
Most of us don't need stability at 150 mph.
Research.
Test your car in a coastdown.
Change the profile.
Test again.
Repeat.
Test your car at different speeds and find out.
I warn you, it takes a long time to be sure.
There are many variables.
But if you test a car for many months and you consistently get better mileage with one fuel or one tweak, and the cost is less than the benefit?
Make your decision.
It is only hard when the change is almost enough.
It makes me think I haven't explored the possibilities enough.
I am switching to evans coolant, with no water.
It can have big benefits in heat control in the cylinder head, allowing lean burn combustion without catastrophe.
But unlike many engine variables, the only people that have researched this fully aren't talking.
But there is big potential for power=efficiency gains there.
And it helps with corrosion, especially with diesels.
I have a friend running his oil, and effectively, his engine at 260 degrees.
He gained 10% just from this.
But it takes a very good heat control.
There are some very sophisticated radiator and fan controllers for diesels due to their sensitivity to running too cold.
Clutch and transmission in the fan and computer control for the grille and fan.
I presume you guys have read about some of the advanced designs for future cars?
Some of the features are out on the new euro diesels.
Most won't be here due to our diesel.
The consensus seems to be for 1.6 litres as being the ideal compromise with additional power and efficiency gained by variable compression or variable displacement. Direct injection meaning variable injection control, pneumatic or ? controlled valves, infinitely variable.
High compression and premium fuel always comes into it.
Proposals have been made to allow higher pollution and lower taxes with premium fuel due to the benefits, when used efficiently.
Some of this does not apply to diesels.
Diesels can be quite efficient at part throttle.
Gas engines are not.
I am advised that I would love a diesel in town and be unhappy on the highway.
Some info, not really specific links, except for wide open throttle.
http://www.sae.org/servlets/index
http://www.roadandtrack.com/default.asp?section_id=36
Wide Open Throttle and the myth of ac saving gas
There are much more detailed articles in the technical areas addressing the physics. I can't seem to go directly.
The technical areas will have the useful info.
Some of this is much too general.
http://www.roadandtrack.com/article.asp ... e_number=3
Variable Valves
http://www.roadandtrack.com/article.asp ... le_id=5588
Do what improves your car.
It does help to know what is going on, but check your own results.
On the aero drag question, I think a good analogy is speaker efficency.
I use very efficient speakers.
If I increase power to 100 watts, I get a certain level.
If you start with less efficient speakers, the power consumption is not too different to reach the same level at first.
As the level goes up, the gap becomes larger and larger, rapidly becoming enormous.
The drag factor you are fixed on, is the reason that cars are all different in their ideal use, rather than similar.
A streamlined car will become more dramatic in it's differences as drag increases.
A poor design will become more dramatic in the negative, for the same reason.
I said often, which is what my sources say.Captain Goddammit wrote:Incorrect. Premium fuel does not have more energy content. If your vehicle runs better on it, either it isn't tuned properly (often too much spark advance) or has a too high compression for low-octane or is being operated in a way that maximizes knocking (heavy load, high temp, etc.) And MON, Motor Octane Number, is simply a different test, using an engine with more variable load and tuning parameters, as opposed to Research Octane Number, obtained by a test engine with no variables except compression ratio. The octane number you see on the pump is the average of RON (Research Octane Number) and MON. .gyre wrote:I can't get the person at sunoco I want on the phone, but generally yes, but not always.
Premium fuel often contains higher energy content as well as higher octane numbers and then there is MON and so on.
I also said it's not relevant.
I could probably find out exactly what is available, but I see that the sae is still debating energy content vs derived energy from fuel.
I could find out eventually, but there is much disagreement about what mixtures produce energy.
You might compare it to the measuring of food by burning it.
It sometimes has little relevance to derived energy in a digestive system.
Perfectly valid data....for a furnace.
Power and efficiency are two sides of the same coin in this case.Captain Goddammit wrote:They have engines with higher compression ratios mostly to make more power.gyre wrote:Many luxury cars and others are designed for premium for efficiency.
Wiki mentions that driver habits and a full load can create a need for higher octane that would not otherwise exist.
The condition that is most apt to knocking is the combination of heavy throttle, low rpm, and high load. So of course a heavy load will amplify it..
I can't wait to get my daily driver to require premium either by advance or raising the compression to where the engine was designed to run and probably both. As long as more efficiency is obtained, it seems like a good thing.
Actually it did get better mileage at it's peak rpm, and in that case was near top speed.Captain Goddammit wrote:It is, MPG-wise. Like mdmf007 and I have already said, aerodynamic drag increases exponentially with speed. There is no getting around the fact that it takes 4x the power to go twice as fast due to aerodynamic drag. There are other things like rolling resistance, etc. but at speeds over 50-ish to maybe 60-ish, aero drag becomes the main thing you're fighting.gyre wrote:They started trying to sell the 'slow is always better' myth with the 55 mph limit.
Your engine does not run THAT much more efficiently at high RPM that your MPG will increase when driving at speeds over 60 or 70 where you are fighting WAY more aero drag. And you could always shift to a lower gear.
(This assumes all cars are the same shape. Even IF 4 times the power is required, that does not translate to 4 times the fuel in all cases. A low drag car at 15 mph will be creating more of the same low drag as speed increases. The difference gets wider, not narrower. Gyre)
How fast your vehicle is capable of going at full power has zero to do with what it's most efficient cruise condition is. Full speed is about the worst for efficiency.
(Power and drag have EVERYTHING to do with best cruise speed. Gyre)
Oh, and larger tires are a tradeoff too. If they are heavier, you will lose efficiency. The most important and effective place in an entire vehicle to remove weight is the wheels, by far. A pound of weight off the wheels and/or tires is MUCH more effective than a pound of weight off the body or chassis.
Smaller, lighter wheels will return the highest MPG. (on wheels, all true. Gyre)
An unusual engine design in the usa, italian car.
I found it too noisy, but I did not in fact have another gear to shift into.
But the mileage was higher.
I was shocked too.
The power curves were in the owner's manual.
Interestingly, the gov website touts the 'slow driving saves gas' still and mentions air drag, but it's own chart of the mythical "regular car" shows an increase in mileage as speed increases and a long plateau before trailing down.
It is all very simple to explain. It's much more complicated than air drag.
A high drag car with a small inefficient engine will probably get better gas mileage at slow speeds.
But what if you don't have a piece of crap?
How about a truck with a very efficient but large engine?
Drag will be a factor quickly, so the gearing must be set for the best load on the engine without so much drag yet. Easy right?
How about a small, very slippery car with a tiny efficient engine?
Until drag overloads the engine, the higher the speed, the better.
You cannot use an engine that maxes at 55 mph if you want a margin for emergencies and running ac.
Such a car will probably use more fuel to run ac at 60 mph than it does to cruise. Stress a car engine too much and it wears too quickly.
See how easy it is to design a car and get it right?
Put a really efficient engine in a truck and you have no power when loaded.
Running empty, the best speed may be high.
Loaded, it could reach peak efficiency at 45 mph.
i know someone with a 660 cubic inch engine in a full size van.
He can tow a 45 foot trailer, two cars, pit crew, 8000 pounds of tools and parts uphill with the ac running in the mountains.
It probably takes more fuel to idle it at 40 mph than it does to propel it.
I know someone with an audi S6 wagon.
It can achieve 170 mph, so it is much more slippery than it looks.
With aero that good, where do you think the mileage peaks?
I don't know, but I'm guessing faster than a Crown Victoria.
The way drag increases is precisely why every car will vary so much in it's ideal speed for mileage.
A bad design gets worse really quickly.
A good design gets worse equally quickly (if we ignore variables) so the good design still ends up with far, far less drag and the difference gets bigger as speed increases.
Still more complex are variables.
My ford stops flowing air over the grille past 40 mph. If the fan isn't on, it starts overheating past 45 mph.
Let's not even get into beneficial turbulence to reduce separation or the really tricky stuff.
Full speed?
The only thing I've had, that had best mileage at high speed was the fiat with a 5000 rpm efficiency peak.
That engine would run to 10000 rpm though.
The big engine produces 300 flbs of torque off idle.
It has tall gearing.
Driving it at 40 mph I'm just wasting heat.
3600 pounds, 500 hp/500flbs and a slippery body (and 11.5 to 1 compression) and 25 mpg.
I think 100 mph would be the mileage peak.
I'm not saying this is normal.
It does show the variables.
That is not top speed.
Top speed is theoretically 180 mph with current gearing.
I think I could do better, just not interested, unless I get the chance to take it to europe.
Honestly, when you hit 100 in seconds, I'm happy.
The car hasn't been over 150 and I have no plans to do so, even on a track.
125 is a very comfortable, stable cruising speed for it.
They won't let you drive like that here for long distances though.
Please explain what is magical about any speed?
If engine loading doesn't factor into it, then why would any speed be selected over another?
Why don't you go to the burn at 15 mph?
Why don't planes go 55 mph?
The answer is efficiency.
And I remind you that cars and trucks are not theory and they don't all have an identical reaction to drag as speeds increase.
My wagon is great but it has serious drag issues, that climb radically with speed.
The bigger ford was designed for daytona and is much better than it looks.
You're getting into a very complex issue.
All that matters is what you have and can you make it better.
I already addressed narrow tires.
Certain models do have far less drag.
They tend to be slippery, hard surfaced and flexible where they shouldn't be.
I fear I will need to stop one day. Hard.
I use alloy wheels already.
The only option I would use is softer high performance tires in a narrower configuration to compensate for the loss of grip.
What I hear from prius owners is that once they dumped the tires, it was a decent car.
I mentioned the tire option as an easy approach for small gearing changes.
How many motel stops will you have to pay for on a 2500 mile drive if you drive at 15 mph? Will it cost more than you save in gas?
How much time will you save if you drive 15 mph over your ideal, presuming you find that out, again over 2500 miles?
(I used to ride a bike enough to think about these things once.)
Is x mpg worth x hours of your trip time? ( and exhaustion?)
Don't forget tailwinds.
If aero is the only factor, then the existing math for planes should work just fine on cars.
Try it.
There is a great deal of research already done on these issues.
High speed vs low speed driving in germany has been debated for years.
High speed referring to over 120 mph+
It was found that between the two major types of pollution, one increased dramatically.
Further research and better methodology found that the other type dropped equally.
Measurements were for time and not distance, so once that was factored in, it was found that as specific engine efficiency increased (not referring to mileage here) pollution was better managed.
The per mile pollution from a high speed car, even if it was burning more fuel, was equivalent to a car going 62 mph.
You may have a car that peaks at only 40 mph.
Tell me why 40 mph and not 55 mph or 70 mph or 15 mph?
There is no air 'barrier' at a certain speed, unless maybe you have a very fast car. (mach 1)
There is a reason they spend huge sums of money on wind tunnels with rolling beds.
The road is part of the aerodynamics.
A car is much harder to understand than a plane in terms of the effect of air.
We aren't doing basic research.
Most of us don't need stability at 150 mph.
Research.
Test your car in a coastdown.
Change the profile.
Test again.
Repeat.
Test your car at different speeds and find out.
I warn you, it takes a long time to be sure.
There are many variables.
But if you test a car for many months and you consistently get better mileage with one fuel or one tweak, and the cost is less than the benefit?
Make your decision.
It is only hard when the change is almost enough.
It makes me think I haven't explored the possibilities enough.
I am switching to evans coolant, with no water.
It can have big benefits in heat control in the cylinder head, allowing lean burn combustion without catastrophe.
But unlike many engine variables, the only people that have researched this fully aren't talking.
But there is big potential for power=efficiency gains there.
And it helps with corrosion, especially with diesels.
I have a friend running his oil, and effectively, his engine at 260 degrees.
He gained 10% just from this.
But it takes a very good heat control.
There are some very sophisticated radiator and fan controllers for diesels due to their sensitivity to running too cold.
Clutch and transmission in the fan and computer control for the grille and fan.
I presume you guys have read about some of the advanced designs for future cars?
Some of the features are out on the new euro diesels.
Most won't be here due to our diesel.
The consensus seems to be for 1.6 litres as being the ideal compromise with additional power and efficiency gained by variable compression or variable displacement. Direct injection meaning variable injection control, pneumatic or ? controlled valves, infinitely variable.
High compression and premium fuel always comes into it.
Proposals have been made to allow higher pollution and lower taxes with premium fuel due to the benefits, when used efficiently.
Some of this does not apply to diesels.
Diesels can be quite efficient at part throttle.
Gas engines are not.
I am advised that I would love a diesel in town and be unhappy on the highway.
Some info, not really specific links, except for wide open throttle.
http://www.sae.org/servlets/index
http://www.roadandtrack.com/default.asp?section_id=36
Wide Open Throttle and the myth of ac saving gas
There are much more detailed articles in the technical areas addressing the physics. I can't seem to go directly.
The technical areas will have the useful info.
Some of this is much too general.
http://www.roadandtrack.com/article.asp ... e_number=3
Variable Valves
http://www.roadandtrack.com/article.asp ... le_id=5588
thirt33n wrote:gyre and captain
Love that.
We're both after the same thing though, understanding how it all works.
Better, faster, stronger.
"Everything is more wonderful when you do it with a car, don't you think?"
-girl by the fire, watching a tree moved by car bumper in the bonfire
It would be a shame if I had to resort to self-deception to preserve my faith in objective reality.
-girl by the fire, watching a tree moved by car bumper in the bonfire
It would be a shame if I had to resort to self-deception to preserve my faith in objective reality.
-
Captain Goddammit
- Posts: 8589
- Joined: Sat Sep 06, 2003 9:34 am
- Burning Since: 2000
- Camp Name: First Camp
- Location: Seattle, WA
A certain engine will have an rpm and throttle setting at which it achieves it's maximum efficiency. That is not the whole picture, that's a static state engine spec. for an engine operating on a dyno in a lab.
You can vary gearing to make it operate at that level at whatever vehicle speed you want.
Aerodynamic drag increases with the SQUARE of speed. Pushing a vehicle at high speeds requires a lot more energy per mile.
Running an engine at full throttle usually results in the production of more power than is needed to maintain efficient cruising speed. Simply increasing speed until the exponential drag increase uses up that power is NOT increasing MPG.
If you ever want to do some real-world road testing and see whether you can get better economy at full throttle or at speeds around 100 mph than I can at part throttle at about 50, in the same vehicle, I'm willing to make a very substantial cash bet.
You can vary gearing to make it operate at that level at whatever vehicle speed you want.
Aerodynamic drag increases with the SQUARE of speed. Pushing a vehicle at high speeds requires a lot more energy per mile.
Running an engine at full throttle usually results in the production of more power than is needed to maintain efficient cruising speed. Simply increasing speed until the exponential drag increase uses up that power is NOT increasing MPG.
If you ever want to do some real-world road testing and see whether you can get better economy at full throttle or at speeds around 100 mph than I can at part throttle at about 50, in the same vehicle, I'm willing to make a very substantial cash bet.
GreyCoyote: "At this rate it wont be long before he is Admiral Fukkit."
I've been hypermiling since I got my '91 Geo Metro. I still get 53 mpg at 55 mph. This year I'm hauling a 5x10 motorcycle trailer so I expect a lower number this year. I took the rails off and put down a 4'x8' plywood floor. The simple ball hitch required only three holes to be drilled using two preexisting holes in unibody. I got it on Amazon for about $130.00 on my Visa card. Plywood was $35.00 from OSH on my Visa card. I used the trailer rail bolts through the wood. I've got a 5 inch gap between wood and outside trailer frame box member. I think I might build a box with 2x4's and three 2'x5' plywood pieces I got off Craiglist for free. I was just going to build a generator sound box but I think I'll double-use it on the trailor. A two foot high chariot box behind my Geo shouldn't be too much of a drag. I've got some bird netting to use to secure my boxes and tents and what-not. I think I'll leave the backend open to reduce drag. -or- I could just put the plywood down flat and just net over the load for a lower profile . My car has a 10 Gal. tank giving me about 500 miles between fillups. I gass-up at home town, topoff in Reno, topoff in Lovelock, topoff in Gerlack, topoff in Reno, and final topoff back home. I have a six station plan.
All true.Captain Goddammit wrote:A certain engine will have an rpm and throttle setting at which it achieves it's maximum efficiency. That is not the whole picture, that's a static state engine spec. for an engine operating on a dyno in a lab.
You can vary gearing to make it operate at that level at whatever vehicle speed you want.
Aerodynamic drag increases with the SQUARE of speed. Pushing a vehicle at high speeds requires a lot more energy per mile.
But the actual total drag at any speed will be different for each car.
And the amount of power available affects the outcome too.
This is why I recommend real world testing.
I was working on an air dam design tonight at a friend's shop.
I will pull the roof rack off unless I use it too.
This depends on the quantity of drag, etc, etc.Captain Goddammit wrote:Running an engine at full throttle usually results in the production of more power than is needed to maintain efficient cruising speed. Simply increasing speed until the exponential drag increase uses up that power is NOT increasing MPG.
It need not be full throttle though, but sometimes it is ideal.
Wide open throttle is most efficient for an engine for some seemingly paradoxical reasons and I don't feel confident at explaining the physics adequately.
But we both agree there are many other things that come into play.
The balance between all loads on the engine is complex and changes when weight and other variables are altered.
Often peak ideal engine speeds are undesirable due to noise, wear and other reasons.
For cruising, I think it is unusual for an engine to have peak efficiency rpm and wot speed occur at the same time.
I do think it is desirable.
But as I pointed out before, if you design for mileage and you have power for ac and emergencies, you will not be at the ideal setting cruising.
This is why the variable displacement engines have been proposed.
Do I get to pick the car?Captain Goddammit wrote:If you ever want to do some real-world road testing and see whether you can get better economy at full throttle or at speeds around 100 mph than I can at part throttle at about 50, in the same vehicle, I'm willing to make a very substantial cash bet.
In the ford, 100 mph is at shallow throttle.
I don't know what cruising is at wot.
It has never come up.
I imagine 20 mpg at 100 mph.
Not meaningful in this country.
I'm probably at half throttle at 120 mph.
In my volvo, I run at a lower rpm than is probably best, for noise and wear reasons.
Part throttle when lightly loaded at 75 mph.
Full load and it is almost at wide open throttle.
I can sometimes not maintain overdrive with a full load on a hill.
I don't know where peak efficiency would be on this car.
But air drag is a major factor on this one.
I would guess peak mileage could not be over 85 mph and possibly as low as 65 mph.
But I have no idea.
My point is, it all depends.
Coefficient of drag is not the only factor to consider.
An efficient car aerodynamically will have increased drag as speed increases, but still be more efficient than a less efficient design.
And turbulence complicates the math drastically.
Small narrow motorcycles often have more drag than automobiles.
Good designs are more competitive as speed increases than bad designs.
For example
4 X 1 = 4 ........ 4 X 10 = 40
4 X 4 = 16 ...... 4 X 40 = 160
4 X 16 = 64 .... 4 X 160 = 640
You can see the direction this takes.
This is why an efficient speaker pays off the louder you play it.
An inefficient design eventually requires an infinite amount of power vs the better design.
Maybe going to the burn, I'll have the patience to test at different speeds.
Judging from other's experience with the same model, I may raise the ideal speed by 10 mph with the air dam.
I am considering smoothing the underside with foam.
The least fuel needed at a particular speed/distance will give you the best mileage.
Due to the physics, the widest throttle opening with the least fuel demanded works best.
With fuel injection, fuel demand and throttle position may not be linear.
There are big discussions on some car boards about this and whether idle is worse than higher rpm cruising.
The hypermilers discuss things most will never think about.
I remember a theory about channeling air through a tunnel to relieve the low pressure turbulence at the rear of a truck in particular.
Crude experiments by a magazine showed promise on a short van.
Benefits should be much higher on a 53 foot trailer.
Catching high pressure air at the leading edge and channeling it to the rear into the low pressure area is the idea.
There may be a lessening of separation on the roof also.
Impressive.Oldguy wrote:I've been hypermiling since I got my '91 Geo Metro. I still get 53 mpg at 55 mph. This year I'm hauling a 5x10 motorcycle trailer so I expect a lower number this year. I took the rails off and put down a 4'x8' plywood floor. The simple ball hitch required only three holes to be drilled using two preexisting holes in unibody. I got it on Amazon for about $130.00 on my Visa card. Plywood was $35.00 from OSH on my Visa card. I used the trailer rail bolts through the wood. I've got a 5 inch gap between wood and outside trailer frame box member. I think I might build a box with 2x4's and three 2'x5' plywood pieces I got off Craiglist for free. I was just going to build a generator sound box but I think I'll double-use it on the trailor. A two foot high chariot box behind my Geo shouldn't be too much of a drag. I've got some bird netting to use to secure my boxes and tents and what-not. I think I'll leave the backend open to reduce drag. -or- I could just put the plywood down flat and just net over the load for a lower profile . My car has a 10 Gal. tank giving me about 500 miles between fillups. I gass-up at home town, topoff in Reno, topoff in Lovelock, topoff in Gerlack, topoff in Reno, and final topoff back home. I have a six station plan.
Have you considered a single wheel trailer?
I always thought they had big aerodynamic advantages for a small car.
The stability is superior too.
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Captain Goddammit
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It seems that you're talking about theoretical ultra-low drag streamliners and I'm talking about most people's existing standard production cars and trucks.
You mentioned "In the ford, 100 mph is at shallow throttle.
I don't know what cruising is at wot.
It has never come up.
I imagine 20 mpg at 100 mph.
Not meaningful in this country.
I'm probably at half throttle at 120 mph."
Exactly... if you then set your throttle to where you were using twice the fuel, in gallons per hour, would your miles per hour double? No. Your mpg would drop drastically.
Aero drag isn't the only thing, but the faster you go the harder you work per mile travelled. In a normal, typical vehicle that most people drive, roughly 50 or 60-ish is where the drag starts outweighing other factors.
That 55 mph speed limit did increase most people's mileage, as much as we all hated it.
But as I said, I've been talking about the cars most of us are driving right now.
You mentioned "In the ford, 100 mph is at shallow throttle.
I don't know what cruising is at wot.
It has never come up.
I imagine 20 mpg at 100 mph.
Not meaningful in this country.
I'm probably at half throttle at 120 mph."
Exactly... if you then set your throttle to where you were using twice the fuel, in gallons per hour, would your miles per hour double? No. Your mpg would drop drastically.
Aero drag isn't the only thing, but the faster you go the harder you work per mile travelled. In a normal, typical vehicle that most people drive, roughly 50 or 60-ish is where the drag starts outweighing other factors.
That 55 mph speed limit did increase most people's mileage, as much as we all hated it.
But as I said, I've been talking about the cars most of us are driving right now.
GreyCoyote: "At this rate it wont be long before he is Admiral Fukkit."
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CapSmashy
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I am having to rethink the entire trip this year.3500 miles for the round trip, give or take a hundred or so.
'
My 2 options, my big ass Dodge with my camper and all my stuff with a trailer that will hopefully get 10 mpg, but I am budget planning at 7mpg.
Or, my 160k miles on the clock VW Beetle TDI. Significantly reduced cargo capacity even with a small trailer and a roof rack, but I should be able to squeeze out 30mpg on the highway with it loaded up. I'll have to load it down and do some practice runs though since I have never had a trailer on it before to see what kind of millage hit it takes with a load. It currently gets 45 to 48mpg.
What is diesel going for out west? Its at about $4.75 here now at the high end.
Playawaste Raiders cordially invites you to suck it.
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JezebelinHell
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Hey, quit with all the intellectual pandering. You're missing out on the most important point. You're pretty much all coming through RENO. Just throw all your gas and food money down on the blackjack table and you'll be fine. I know, because I watch people do it with their rent checks all the time. What's the worst that could happen?
"The future is a whore, she promises herself to everyone."
--Poe
--Poe
No, I'm talking about all cars.Captain Goddammit wrote:It seems that you're talking about theoretical ultra-low drag streamliners and I'm talking about most people's existing standard production cars and trucks.
I used some dramatic examples for illustration.
The volvo is dead stock.
I had a pontiac 6000 with the 4 cylinder.
You can't get more average and technically unsophisticated than that.
But with a fairly slippery body, it got 32 mpg at 75 mph with the ac running, much to my shock.
I could find no measurable improvement at slower speeds.
What matters is how the car you have behaves.
But it is good to know.
There really is nothing magical about a specific speed for all cars.
True.Captain Goddammit wrote:You mentioned "In the ford, 100 mph is at shallow throttle.
I don't know what cruising is at wot.
It has never come up.
I imagine 20 mpg at 100 mph.
Not meaningful in this country.
I'm probably at half throttle at 120 mph."
Exactly... if you then set your throttle to where you were using twice the fuel, in gallons per hour, would your miles per hour double? No. Your mpg would drop drastically.
Engines do not perform in a linear fashion under load though.
I only recommended wide open throttle for acceleration to cruising speed.
Steady driving really is a major factor in mileage, perhaps outweighing all other things in today's traffic.
The ford, although highly modified, has a bone stock body except for the front and rear caps, which I doubt alter drag.
A stock version with the stock 5 litre would still get best mileage over 70 mph, if geared properly.
It is an unusually sleek body design, but not small or light.
There are many fairly good aerodynamic designs sold now.
The audi I mentioned is a stock body and engine.
It is powerful, but the drag must be very low on it.
You wouldn't guess by looking.
I simply disagree with this.Captain Goddammit wrote:Aero drag isn't the only thing, but the faster you go the harder you work per mile travelled. In a normal, typical vehicle that most people drive, roughly 50 or 60-ish is where the drag starts outweighing other factors.
That 55 mph speed limit did increase most people's mileage, as much as we all hated it.
But as I said, I've been talking about the cars most of us are driving right now.
The government tried like crazy to prove this, finally giving up and saying it was all about safety.
As you say, what you have to drive and what it really does is what counts.
I had planned to tow a trailer this year.
That is now out due to fuel prices.
I have a trailer that is a very light tube frame design on an independent torsion bar suspension.
I have found that the right suspension on a trailer makes a big difference as jerking and bouncing between the two things are minimized.
Even so, there is an increase in drag, so I am certain that the optimum speed drops quite a bit.
Your towing rig may actually peak at 45-55 mph.
If you are driving a diesel, possibly less?
I know the diesel ambulance I was interested in for conversion, probably peaked at 45-55 mph because it was not a turbodiesel and was certainly not a low drag design.
Improving what you have is all that matters here.
I do urge anyone with a truck in particular to look at aero improvements they could do.
I would have definitely belly panned that ambulance.
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Apollonaris Zeus
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Hey, I'm not spending a dime on gas this year. I'm going hobo style. Jump'n the train and getting off at the water tank. UPS will deliver my 4 boxes of stuff at center camp. After the event everything is burnt, I walk across the playa, hop on the train and Im back in two and half days!
AIIZ
Really...?
AIIZ
Really...?
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Captain Goddammit
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- Camp Name: First Camp
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Kinetik V
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The thread's dead? And we haven't even reached the point of digging into old NACA airfoil designs for homebuilt trailers and aero mods to cars yet! No discussions of electrification of older cars to take gas guzzlers and turn them into "green luxo-rides", 2 cylinder trikes, and all sorts of possible topics.
This thread has only scratched the surface of it's potential. Don't kill it off yet!
This thread has only scratched the surface of it's potential. Don't kill it off yet!
Kinetic V
~~~~~~
I bring order to chaos. And I bring chaos to those who deserve it, wherever that may be.
~~~~~~
I bring order to chaos. And I bring chaos to those who deserve it, wherever that may be.
http://www.roadandtrack.com/article.asp ... e_number=3Captain Goddammit wrote:That statement alone makes it worthless to discuss this any further.gyre wrote: I only recommended wide open throttle for acceleration to cruising speed.
I posted this about wot.
R & T did a much more technical article about the physics involved and you can be sure there is a lot about it in sae papers.
I can't find that article online.
This is very general, and as I said before, short shifting at full throttle is not something I would recommend usually.
It's a quick way to snap connecting rods in some engines.
It may be even more risky for transmissions.
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stargeezer
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I have been trying to stay out of this one, but I can't take it anymore.
NASCAR designs their cars to operate in the 180-200 mph range. They put loads of money into their design both in aerodynamics and engine performance. If cars get better fuel mileage at high speeds, why is it that at the end of many races some of the cars are trying to conserve fuel as they are not sure they can make it to the end of the race and they hope they are lucky enough to get the caution flag out so they drop to 55 mph which conserves fuel and allows them to complete the race without making another pit stop.
Driving at high speeds just wastes fuel no matter how you look at it!!!
NASCAR designs their cars to operate in the 180-200 mph range. They put loads of money into their design both in aerodynamics and engine performance. If cars get better fuel mileage at high speeds, why is it that at the end of many races some of the cars are trying to conserve fuel as they are not sure they can make it to the end of the race and they hope they are lucky enough to get the caution flag out so they drop to 55 mph which conserves fuel and allows them to complete the race without making another pit stop.
Driving at high speeds just wastes fuel no matter how you look at it!!!
If you want to reach for the stars, you better have long arms!
There really is no similarity between steady state cruising and racing.
A race car can conserve fuel by simply not racing, falling into the pack, drafting, not running at the edge of the traction circle in a corner. and so on.
Endurance racing would be the most similar, but it is just not the same thing.
And pure race cars, that is cars never driven on the street at all, have some fundamental differences in suspension settings and engine tune.
Race cars are always a compromise between ultimate grip and low drag.
Often there is massive drag dialed in to stabilize the car at high speed.
NASCAR has required a certain level of this for safety.
Some cars are theoretically capable of running upside down at high speed.
There is a cost to this in drag.
During a certain period in F1, the cars were developing so much downforce, that if they were unsettled, they might fly off the track.
This is a fascinating area, but not relevant to the average car.
My volvo airdam should reduce lift and improve high speed stability, as well as reducing drag.
But there are only some things you can do that reduce drag and enhance stability before you start trading off for increased drag on a car.
Many sports cars and luxury cars do this already.
It is not a point that people trying to increase mileage will usually want to cross.
If you want to see useful things done on the track that may cross over to the street, look at the high speed steady-state testing done to set fuel mileage records.
__________________________________________________________
Racing is life.
Everything else is waiting.
A race car can conserve fuel by simply not racing, falling into the pack, drafting, not running at the edge of the traction circle in a corner. and so on.
Endurance racing would be the most similar, but it is just not the same thing.
And pure race cars, that is cars never driven on the street at all, have some fundamental differences in suspension settings and engine tune.
Race cars are always a compromise between ultimate grip and low drag.
Often there is massive drag dialed in to stabilize the car at high speed.
NASCAR has required a certain level of this for safety.
Some cars are theoretically capable of running upside down at high speed.
There is a cost to this in drag.
During a certain period in F1, the cars were developing so much downforce, that if they were unsettled, they might fly off the track.
This is a fascinating area, but not relevant to the average car.
My volvo airdam should reduce lift and improve high speed stability, as well as reducing drag.
But there are only some things you can do that reduce drag and enhance stability before you start trading off for increased drag on a car.
Many sports cars and luxury cars do this already.
It is not a point that people trying to increase mileage will usually want to cross.
If you want to see useful things done on the track that may cross over to the street, look at the high speed steady-state testing done to set fuel mileage records.
__________________________________________________________
Racing is life.
Everything else is waiting.
I thought this was interesting.
The SmILE is a car modified by Greenpeace for better economy.
Note that the engine is of a more advanced type.
Some of the statements about engines are misleading or inaccurate, but I think the improvements they are claiming are fairly realistic.
From Wikipedia:
A smaller and more efficient engine, a supercharged two-cylinder four-stroke internal combustion engine with four-valve technology in a boxer arrangement. A maximum torque of 75 N·m results from a swept volume of 358 cm3 at 2,900 rpm. The dynamic pressure supercharger makes sure the engine runs most efficiently at normal operating speeds. Most car engines are designed for optimum performance at maximum speed and load, which are in reality rarely used. At 55 bhp, the engine has the same performance as the original Twingo. Other performance parameters, such as maximum speed, elasticity and acceleration are the same or better.
http://en.wikipedia.org/wiki/SmILE
http://archive.greenpeace.org/climate/s ... table.html
http://archive.greenpeace.org/climate/s ... index.html
http://archive.greenpeace.org/climate/s ... /faq3.html
http://archive.greenpeace.org/climate/s ... index.html Photos
The SmILE is a car modified by Greenpeace for better economy.
Note that the engine is of a more advanced type.
Some of the statements about engines are misleading or inaccurate, but I think the improvements they are claiming are fairly realistic.
From Wikipedia:
A smaller and more efficient engine, a supercharged two-cylinder four-stroke internal combustion engine with four-valve technology in a boxer arrangement. A maximum torque of 75 N·m results from a swept volume of 358 cm3 at 2,900 rpm. The dynamic pressure supercharger makes sure the engine runs most efficiently at normal operating speeds. Most car engines are designed for optimum performance at maximum speed and load, which are in reality rarely used. At 55 bhp, the engine has the same performance as the original Twingo. Other performance parameters, such as maximum speed, elasticity and acceleration are the same or better.
http://en.wikipedia.org/wiki/SmILE
http://archive.greenpeace.org/climate/s ... table.html
http://archive.greenpeace.org/climate/s ... index.html
http://archive.greenpeace.org/climate/s ... /faq3.html
http://archive.greenpeace.org/climate/s ... index.html Photos
This is what I think of as high speed driving.
Much can be done on a normal car, but it is much easier on a truck.
If you do this pay attention to cooling of the drivetrain.
It has been taken as far as sealing the engine bay on some experimental cars.
http://privatenrg.com/#Undercovers
Some mileage comparisons on the Prius
Note that as a low drag vehicle, slight variations have a more dramatic effect. He says that an 8 mph wind, changing direction can cause a 10 mpg change.
In this worst case scenario of wind direction, even the Prius with a low power engine gets reasonable mileage at 105 mph.
http://privatenrg.com/Papenburg.htm
This overview of mileage simulators shows how many factors are involved in affecting mileage.
The Prius is a moderately slippery body, not that small and with low power, so the expectation would be for good mileage trailing lower as speed increases, which the charts seem to show.
Note that mileage does not abruptly drop as speed increases, but gradually decreases.
I have noted a great sensitivity to wind myself in light cars.
http://privatenrg.com/
This picture shows the bellypan on a Prius.The ThrustSSC record was achieved by British RAF pilot Andy Green on 15 October 1997. It was set in the Black Rock Desert in Nevada, USA. Thrust Super Sonic Car's two jet engines produced a combined total of 100 thousand pounds-force (440 kN) of thrust force. During its record-breaking run, Thrust SSC accelerated to 600 mph (970 km/h) in just 16 seconds and became the first car to break the sound barrier.
Much can be done on a normal car, but it is much easier on a truck.
If you do this pay attention to cooling of the drivetrain.
It has been taken as far as sealing the engine bay on some experimental cars.
http://privatenrg.com/#Undercovers
Some mileage comparisons on the Prius
Note that as a low drag vehicle, slight variations have a more dramatic effect. He says that an 8 mph wind, changing direction can cause a 10 mpg change.
In this worst case scenario of wind direction, even the Prius with a low power engine gets reasonable mileage at 105 mph.
http://privatenrg.com/Papenburg.htm
This overview of mileage simulators shows how many factors are involved in affecting mileage.
The Prius is a moderately slippery body, not that small and with low power, so the expectation would be for good mileage trailing lower as speed increases, which the charts seem to show.
Note that mileage does not abruptly drop as speed increases, but gradually decreases.
I have noted a great sensitivity to wind myself in light cars.
http://privatenrg.com/
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cowboyangel
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Captain Goddammit
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Hell, I'm puttin' over $40 at a time into my Miata! Fortunately that lasts about two weeks. My truck is well over $100 to fill, and it's empty before you know it. Nowadays I only drive it when I actually need it to carry or pull something.
GreyCoyote: "At this rate it wont be long before he is Admiral Fukkit."
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Marscrumbs
- Posts: 543
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- Location: Bishop Ca
octane
So true, for example both ethanol and propane are have a higher octane value but less fuel density. Rose oil contain an n-chain octane oil which has an octane value close to zero. Also cost thousands a gallon but would make your car smell great mixed in with higher octane fuel.mdmf007 wrote:Octane rating only refers to the ability to spontaneously detonate. It gives no more power over lower octane ratings.
Where you do get more power in higher octane ratings is in engines that need it, these engines run at a higher compression rate. A lower octane rating run in a higher compresion engine, will knock, or pop the heads off. The fuel is detonating on its own before the piston is at TDC (Top Dead Center) in effect trying to shove it back down, before its all the way up. Higher octane resists this urge and allows the spark to blow it off.
a higher octane rating in an average engine makes no difference in power or efficiency
Wind resistance is a function of the square. resistance at 100 MPH isnt simply twice that of 50MPH. So i would have to believe that there is a happy medium.
later