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35

If the car is equipped with a modern fuel injection system, it will likely use less if left in gear and allowed to run against the transmission with no throttle as modern fuel injection systems can and do shut down the injectors completely thus use no fuel whatsoever. If the engine is at idle in neutral, the ECU will have to use a small amount of fuel to ...


19

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 ...


16

That is a great question. I believe the true answer here is "it depends". Like so many other things you can do with your vehicle, if your vehicle cannot use the higher octane fuel, it won't benefit from it. Something to remember about octane ratings is, the higher number does not mean it is more energy dense. The higher number indicates the fuel is actually ...


13

I can't give you numbers or calculations without some work, but I can tell you than energy is never free. Cars have an A/C compressor that is mechanically driven by the engine because this is the easiest way to get the job done in a typical consumer car. An A/C compressor actually takes a huge amount of energy to operate. In fact a central A/C unit for a ...


12

It absolutely does use more fuel. What the choke does is creates a restriction in the carburetor, which in turn creates a higher vacuum so the engine will draw more fuel when it is cold. This is called fuel enrichment. It allows the engine to warm up and keep running, but at the expense of using more fuel to make it happen. When leaving the choke on for a ...


11

One of the reasons is loads of extra weight added by safety features and options. 8 airbags, 12 speaker stereo, 14 way adjustable seats, tons of insulation all around, power windows, power locks, 18 computers with hundreds of sensors, etc. Also consider the size/power output of the engine. It looks like your car had a 4 speed manual. Most cars today ...


10

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 ...


10

Well, Teslas (and presumably other all-electric cars) have A/C so it's not impossible, but A/C takes a fair amount of power. On the other hand, Teslas store a lot of energy. The A/C is something like 2.4kW which is about 8,000 BTU/h or about 3HP. So using an electric motor on a conventional car might give you a few more HP briefly, but the alternator has ...


9

If you're looking at just the fuel consumption whilst going downhill, then yes, as Steve Matthews said you'll use less fuel if you're in gear and foot off the throttle - likely no fuel at all. But you also need to consider after the hill - if you don't brake and allow the car to freely accelerate down the hill, you'll then have considerably more speed than ...


9

As Steve Matthews noted, modern cars will not use fuel while coasting downhill in gear. This is called Deceleration Fuel Cut-Off and uses various sensors to determine the engine load (i.e. the car is driving the engine) and whether the throttle is at idle (i.e. the driver's foot is off the pedal). The engine computer will then stop injecting fuel. Generally ...


8

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. ...


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

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 ...


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 ...


8

Something to keep in mind is that the time an engine takes a great deal of its wear is cold starts. The oil isn't up to temperature yet, so parts are not separated as they should be and you get more wear. If you do this very frequently, like going from red light to red light, you're probably doing more harm than good. Also, if your car does not start as ...


8

The short answer to your question is no. As @JPhi1618 noted, the compressor is mechanically driven. Without the compressor you don't have any cooling. The AC runs by changing the state and pressure of a liquid, and compressing the liquid is a big part of that cycle. If you bolted an electric compressor onto the car you would have to find a way to switch ...


7

The short answer is no. The engine is most efficient at the RPM when maximum torque is achieved. It's easiest to explain with a picture. Power is a function of torque and RPM. Maximum torque is achieved because the engine is able to move the maximum amount of air and fuel in and out of the engine. The power continues to climb even when the torque starts ...


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 ...


7

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 ...


7

Modern gasoline engines have sensors to measure the amount of air that enters the engine. The ECU then injects fuel to give the correct mixture to get the most efficient burn. A dirty air filter will first show itself by limiting the flow of air at high throttle positions. Rather than causing a rich mixture however, the ECU will see the low air flow and ...


7

fuel injected vehicles don't require a crazy amount of fuel to get started, in terms of fuel economy alone anything over 30 seconds should be safe (although we are talking about levels of fuel only eco-modders care about). If you are concerned about wear, there's no good way to tell which is better. If you change oil regularly I wouldn't worry about the wear ...


7

wear is increased at engine start When you have no oil pressure and you start the car, that is when the most wear occurs on your bearings. Crank bearings in most cars are not roller bearings anymore. They are called plain bearings and rely on hydro-dynamic lubrication. Here is answer related to crank bearings with illustrations so you can understand ...


6

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 | +---------...


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 ...


6

Engine control systems in typical cars do not generally change the spark advance to add more than expected, the engine is designed to run at a particular efficiency for a given octane, so changing it from whats specified by the manufacturer isn't a good idea. If there is sub optimal conditions and the engine management detects a problem, fuel mix or knock ...


6

Two great comments already; couple of things to add. The reason why we have Octane types is because the lower-octane fuels tend to ignite at lower temperatures (ie. hot metal parts inside the combustion chamber, rather than the spark plug firing) or lower compression pressures (ie. the compression fires the engine like a diesel engine works). The octane ...


6

I'd suspect that it is causing extra wear on the starter motor and flywheel (where the starter motor engages). Considering the start isn't in motion at any point other than starting the car, and there's no contact between it and the flywheel unless you are running the starter, you are causing more wear. Depending on the cost of replacing those parts, it ...


6

Yes, this is possible. Several companies (VAG, BMW) have switched to AC units that are driven by electric motors. For BMW, this is part of their Efficient Dynamics strategy, where they'll switch the compressor on/off depending on engine load to optimize fuel consumption. When the weather's not too hot, you can run the compressor intermittently without the ...


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

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 ...



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