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17

Lean ≠ More Air I believe the source of the misunderstanding is in how the term "lean" is being interpreted. A lean mixture doesn't indicate the presence of more air. It indicates the presence of a higher proportion of air compared to fuel (air-fuel ratio, or AFR). Quick example Mixture A has 1,000 g of air, 80 g of fuel. AFR = 1000/80 = 12.5 ...


9

As DucatiKiller notes, coasting downhill in neutral is usually considered unsafe, as it increases the chances of overheating your brakes. It is also illegal in many jurisdictions. Questions about driving techniques are generally off topic here, but you do have a question about how engines work that I think is (maybe marginally) appropriate: why do you get ...


9

A couple of things to contemplate: You need a certain amount of power at the wheels to maintain a certain speed. This assertion is (correctly) made in the question. At 100 km/h, a typical sedan would require roughly 10 hp at sea level to overcome the forces due to aerodynamic drag and maintain speed¹. The fact that an engine can produce 100 hp or 300 hp ...


8

Gasoline is made in large batches. Each batch has a number of attributes that should be met; Octane, specific chemistry, volatility, contaminates, ethanol content, and others. The output is dependent on the crude that went into the refinery and the processes the refiner has at hand to process it. Refineries vary in there capabilities. There are over 60 ...


8

It's not that the catalytic converter can't handle more air per se, it's that running lean increases the temperature of combustion (I actually don't know why, but now I'm curious) and the catalytic converter needs to run inside it's chemical operating range. Something to do with the chemistry that I also don't know. As for advantages for turbo boost and ...


7

I work for a fleet delivery service. Due to safety regulations all vehicles must be shut off at every delivery point. This equals up to 150 stops a day. The starter motors fail with regularity. In most cases 3 times or more a year. Ignition switches about twice a year, and fly wheels every 2 years. While you won't see this type of abuse,stuff will wear out. ...


7

Vehicles use fuel because the energy in the fuel goes to these uses: Air resistance. Because vehicles aren't moving in a vacuum, the air has a resistance force and because force times distance is energy, this uses energy. Rolling resistance. Although tires eliminate friction, there is little rolling resistance that converts kinetic energy to heat when ...


6

Lean operation vs exhaust catalysts: The three-way catalytic converter fitted to gasoline vehicles can't operate under lean engine conditions because the reaction of NOx to nitrogen and oxygen is a reduction reaction, and for this to occur there needs to be a corresponding oxidation. In the three-way catalyst that is the oxidation of CO and hydrocarbons to ...


5

Over on the linked question, I talked about how engine braking works to reduce fuel consumption at a high level: Coasting: nothing much. The transmission is effectively disengaged (it's more complicated than that but it's a reasonable approximation). The engine is idling - burning fuel to keep itself spinning. Engine braking: the transmission is ...


5

Background This is a common issue with shim and bucket valve trains. As the valves are getting worn into the head a small groove is beat into the valve face after opening and closing so many times. As the valve pushes up into the head it takes up clearance between the cam lobe and the bucket which the cam lobe depresses to push the valve in and open it to ...


5

The oil stuff is more than likely caused from what the intake pulls out of the crank case through the PCV. If you can get a hold of a couple cans of Seafoam, this should take care of the residue about as easy as you can do it without taking the engine apart. Use the rubber hose to the right of the photo to introduce it into your system. As an engine gets ...


5

BSFC is just engineer-speak for how much fuel is consumed by the engine per unit of energy output¹. This webpage provides a very concise comparison for several different engines: +------------------------------------------+----------+----------------+-----------+ | Engine | @ 1K RPM | @ Peak Torque | @ Peak HP | ...


5

That pipe probably goes to the tank too, it is just there to let air out of the tank while adding fuel down the main pipe. I believe that your additive will be in the fuel.


5

Just so we're on the same page as to how two strokes work, here's a pic. I had to look it up because I had the wrong picture in my head. In looking at how the cycle actually works, the power stroke goes off creating the combustion products and power. As the downstroke begins the pressure in the cylinder is high allowing the exhaust gases to escape and ...


5

There is Brake-Specific Fuel Consumption Which is a measure of how much fuel is consumed per unit energy. Another way to look at it is the rate of fuel flow needed per unit power developed by the engine. This information is not something accessible through OBD-II. But it's not very useful in this case Note that MPG remains relevant because it is a ...


5

In a perfect world from a physics textbook, you might be able to ask the question you have, and expect to compare time vs. engine speed, but there are many more factors in the real world. The speed-agnostic measure is Miles Per Gallon (or l/km). Speed doesn't appear in the name, because it doesn't matter. At higher speeds, things like wind resistance and ...


4

The generalized statements about the gaps being too small causing insufficient burn and too wide having a weak spark are spot on. As you widen the gap, you need to increase voltage to cover the gap. Also, as you increase pressure at the top of the compression cycle, you'll need to either increase the voltage output to the spark plug and/or reduce the gap of ...


4

This is an average of the figures for constant speed (highway) driving in top gear and city/traffic driving with lots of gear shifts. The ratio is usually 50/50 so they'll measure e.g. 100 miles of highway driving, then 100miles of city driving, add the figures together and divide by two to get the combined average. Though to get those same figures, you're ...


4

Lower "cold side" of the Carnot cycle leads to better theoretical efficiency, sure, but have you calculated how much? 10-20 K colder intake with the same 1000 K combustion temperature affect final efficiency by 1%. And that efficiency is 70% in any case, so you can guess that there are so many more parameters lowering the final efficiency to 25%, that the ...


4

I have a 2013 Honda Civic EX Sedan. The ECON mode, from my research and personal experience with my car, does the following: changes the shift pattern of the transmission to maximize mpg by limiting downshifts unless you "floor it", reduces the A/C compressor operation and A/C fan to conserve mpg, changes the throttle response to maximize mpg and adjusts ...


4

Mileage of a car is based on a ton of factors but since you are concerned with a specific speed range it comes down to one thing Air resistance. Air resistance: There is very minimal difference in the air viscosity between 70 to 90 kmph but when you go more than 110 the air starts to get thick , simply put , if your car's aerodynamics are optimum to handle ...


4

Typically if you're doing any kind of speed, roof up with be more aerodynamically economical although I personally didn't notice much difference on either of mine. That said, I didn't pay much attention to fuel consumption in either of those cars.


4

Though There are many geeky ways to calculate fuel economy this one is one of the easiest ways to calculate. Fill up your car's tank all the way. If your car has a trip odometer, reset it, or record the master odometer mileage. Drive your car as you normally would, and let your tank deplete to at least a half of a tank of fuel. Get to the fuel station and ...


4

If the location shown in your profile is accurate, ambient pressure should be around 29.7 in Hg, so your neighbor's car seems to reflect the correct altitude. As @barbecue mentions, Wolfram|Alpha shows that 29.2 in Hg reflects an altitude of 205 m (674 ft) above sea level. If you compare the air densities resulting from these two readings, the percentage ...


4

On most vehicles, the larger the engine the more fuel it burns. The 5.8L size is the displacement (or swept volume) of all the cylinders (eight in your case) added up. When the cylinders fill with the air/fuel mixture, this mixture should be stoichiometric at about 14:1 ratio (no matter what kind of gas/petrol engine you run, this is basically what you are ...


4

A lot of that depends on the type of vehicle, and your definition of 'fast'. Take this with a grain of salt, but a while back BBC's Top Gear did a test involving a V8 powered BMW M3 and a Toyota Prius. The Prius was driven as fast as it could go around their test track, while all the M3 had to do was keep up. After a few laps, the Prius had done ~18 mpg, ...


3

Just measure your actual MPG by filling your tank all the way, then divide how many miles you drive until the next fill up by the number of gallons of said fill up. My mileage was off with a similar setup because I had larger aftermarket rims and tires, which means the car travels a longer distance for each rotation. Even a different profile tire can make a ...


3

Considering on this website they say you can figure out the amount of CO2 emissions per km based on the fuel mileage, I'd suggest they are saying the rate of emissions is proportional to the MPG (given their constant). This makes sense to me because there are so many carbon atoms in a gallon of gas. When burnt (correctly), the CO2 emissions are going to be ...


3

The level sensor works with essentially sliding contacts. These contacts wear out over time and crud, dirt and corrosion can build up on them. Did i mention that the sensor is submerged in gasoline. Some cars have known problems with level sensors but i'm not aware of BMW specifically having a problem. If you don't want to spend any money this problem can ...


3

If the Barometric sensor (BARO) is incorrect will the fuel mileage will be affected? It depends, and only rarely . In control systems that use MAF sensors such your Azera the BARO is not needed except as backup to the MAF sensor. The MAF sensor measures the mass of the air entering the engine which is used by the PCM to decide how much fuel to mix with it ...



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