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Engine, Fuel System
#241 of 297 Gasoline providers
Feb 09, 2007 (11:02 am)
I'm not sure if this is the right forum but hopefully someone can educate me on gasoline providers.
I live in an area where the gas stations are dominated by the local convenience stores, Rutter's, Sheetz, Tom's, etc. Reading a few forums, the discussion of top tiers gasoline providers popped up. It dawned on me that none of these providers are in my area (South Central PA) or are they? Is there a way to find out who provides the gas for these stations? Obviously Rutter's and Sheetz don't own refineries and must buy from someone.
#242 of 297 Gasoline providers
Feb 12, 2007 (11:27 pm)
These are most likely UNBRANDED providers who load up their trucks at the local refinery and sell to local convenience store chains, among others, in your area. It's basically the same gasoline that you would find at the branded stations.
Jul 10, 2007 (4:29 pm)
I read a lot of car forums for many different reason. But there seems be a common post in just about all the forums, GAS MILEAGE.
Many people get upset or can not understand why the GAS mileage of same vehicles differs so much. It is quite simple and it is not what most people talk about. Yes how you drive has a lot to do with it but the one main reason that mileage differs on two like vehicles is ALTITUDE.
ALTITUDE will determine how lean or rich your car will run. Higher altitude will provide better gas mileage if your car is tuned properly for the higher altitude.
Here is a simple explanation of what I mean.
With altitude, air density decreases, so a computer controlled fuel injection system will automatically decrease the fuel in the mixture to match the air density. Thus all the electronic sensors needed to keep the motor running correctly. You will find that horsepower will decrease, but mileage will actually increase.
This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the fuel mixture after reaching cruise altitude, you leave the fuel mixture at full-rich while climbing.
I hope this help explain why gas mileage is so different from so many people. The higher the altitude the better mileage. So people in Denver get better mileage then people in Death Valley California.
If you need a better explanation your local mechanic can also explain this to you.
#244 of 297 Re: Gas Milage [calisteel]
Jul 11, 2007 (11:29 am)
But the computer adjusts the amount of fuel to match the air and the load on the motor. The amount of unburned oxygen in the exhaust is measured by the O2 sensor and the car will have to do the same amount of work to move the car 1 mile so the same amount of fuel is going to be used.
#245 of 297 Re: Gas Milage [imidazol97]
Jul 11, 2007 (11:52 am)
Not true. At a higher altitude your fuel mixture will be less as well as your power output. You move the same 1 mile at the same rate but through less dense air, so less power is needed thus lessening the fuel needs as well.
In thicker or more dense air you need a more rich fuel mixture increasing the power output to move you 1 mile thus burning more fuel.
Even though the car is doing the same speed and distance the output of fuel needed is greater or lesser depending on the fuel mix based on air density. You can not get around it.
Jul 11, 2007 (12:19 pm)
I thought the computer kept the mixture the same. The air valve in the throttle body lets more or less fuel mixture into the intake manifold to give more power.
What is the difference in air resistance at 900 feet altitude compared to 0 feet?
#247 of 297 Re: Gas Mileage [calisteel]
Jul 11, 2007 (12:22 pm)
thanks calisteel. your point about altitude is well-taken.
also, it explains why I've been seeing such lousy mpg while driving in the Marianas Trench.
#248 of 297 Re: Gas Milage [calisteel]
Jul 11, 2007 (7:16 pm)
"ALTITUDE will determine how lean or rich your car will run. Higher altitude will provide better gas mileage if your car is tuned properly for the higher altitude."
Ummm, no. Modern fuel injected cars measure the weight of the air coming into the engine and provide the exact same amount of fuel per pound of air at all altitudes and all temperatures and all humidities. Fuel economy as measured by the conventional Brake Specific Fuel Consumption (BSFC) measurement won't change one iota regardless of any of the above "Density Altitude" factors.
"This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the fuel mixture after reaching cruise altitude, you leave the fuel mixture at full-rich while climbing."
Ummm, no again. GA aircraft can extend their range at altitude simply because air resistance against the airframe is lower at altitude. Said another way, I take out say a Skylane and set it up as lean as possible to cruise at 100 knots in level flight at sea-level, and then measure the hourly fuel flow. I then take that plane up to say 17,000 feet and lean out to the exact same hourly fuel flow setting, that plane will have a true airspeed of 137 knots. That, and only that, is why aircraft get better economy at altitude.
FWIW, I've seen anecdotal evidence that suggests that cars will see some gains in economy at altitude (but no where near as dramatic as with aircraft due to the rolling friction of the wheels), especially turbo-charged cars.
#249 of 297 Re: Gas Milage [shipo]
by MrShift@Edmunds HOST
Jul 12, 2007 (8:21 am)
I would think you'd need to also advance engine timing at altitude to maintain the same fuel mileage. But perhaps the re-calibration of the fuel mixture negates that necessity?
#250 of 297 Re: Gas Milage [Mr_Shiftright]
Jul 12, 2007 (8:22 pm)
General aviation engines have fixed timing and zero ability to adjust it one bit from where the factory set it and where the FAA certified it.
That said, stoichiometric is stoichiometric is stoichiometric. Given the proper air and fuel ratio, the mixture will burn exactly the same regardless of whether the aircraft is at a density altitude of sea-level or 17,000 feet.