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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 ...


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 ...


12

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 ...


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 ...


9

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 ...


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 ...


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 ...


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

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

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

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

... As the air gets thinner at higher altitudes, your air/fuel ratio is going try to stay the same (emissions, performance, fuel efficency) if you're under the control of the ECU in closed loop mode. Consider the Mass Airflow Sensor, which detects the total mass (not volume!) of air entering the engine by a hot wire resistance sensor. Note that I have no ...


5

Technically speaking, coasting in neutral may save you some gas, because mechanical losses in the engine at ~3000RPM are greater than the power needed it run it idle at ~500RPM. Coasting in gear won't consume any gas, but it will slow you down faster, requiring you to reaccelerate earlier than you'd have to when coasting in neutral. However, if you're in ...


4

The gas gauge is just an indicator and each vehicle is going to be different. I know the older Datsun Z cars had two gas gauges, one was the main one which showed the volume of gas down to 1/4 tank, while the secondary one showed from 1/4 down to empty. The secondary gas gauge was very accurate to give the driver a true indication of how much fuel was in the ...


4

TL;DR: On my experience - Long hills on gear, short slopes in the city - on the neutral (not breaking the limits of speed and sanity). On my petrol powered '97 MMC Galant i've got a custom made trip computer for counting fuel consumption, that is hooked up directly to the fuel injector wires. Here's my observations: when coasting downhill at 4-th gear (i've ...


4

Each car is a bit different but the highest efficiency for automatic transmission acceleration is usually at the point before the the transmission decides to automatically downshift. The data you should look for is called "brake specific fuel consumption". This may be a broad generalization, but your highest efficiency for normal gasoline cars with ...


4

There has been a lot of good information shared here, especially by Lawrence Wade (from my perspective). But we're slightly left hanging about the two closely-related fundamental questions from the OP: Will higher octane fuel, increase power while towing? and Will higher octane fuel impact the available power in common v-6 regular gas burning ...


3

A lot of people get confused with octane ratings. The octane rating is the fuels resistance to detonation, ie, the fuel / air mix igniting just due to pressure. When this happens the resulting burn is very violent and can easily cause major engine damage. When the fuel / air mix burns normally it pushes down progressively on the piston; when detonation ...


3

Physics suggests that its easier to pull vs push, but based on specific conditions and assumptions. Depends on the vector of the external force of the push / pull and where and how it acts on an object. I believe in a motorized wheeled vehicle, its not nearly as significant, especially since the rotational torques are being transferred to the ground at ...


3

Regarding aerodynamics, the back of the car is just as important as the front. While the front of the car is responsible for cutting though the air ahead of it, the rear is responsible for returning the air to the void that the front created. As seen in the above picture, when the air flowing over and around vehicle reaches the rear edge, it creates a ...


2

The more throttle you apply the worse your gas mileage is going to be. If you want to absolutely maximize your gas mileage, use the minimum throttle possible. So accelerate only enough to just barely creep the speed upwards. On a hill, you would want a constant velocity and use terrain to your advantage. Basically put the car in neutral when going down a ...


2

There are many factors, and some are already covered well above. However on a typical petrol engine the amount of power required is controlled by the throttle. This strangles the flow of air into the engine, and this results in pumping losses. If a car requires (say) 20hp for a constant speed then that is 20% of the available power of a 100hp car while ...


2

There is NO free lunch, you will need many batteries and a much better alternator. You could in fact attach a window mounted air conditioner like @Spehro Pefhany suggests. OR TEC Thermo Electric Cooling There are peltier elements that also generate a cooling effect compressor free. They are essentially a plate of ceramic postively charged, and one ...


1

Engine Position does play a part but its not what you think, RWD cars have the power transmitted to the rear wheels and has to make a 90 degree turn in the differential, resulting some power loss (fuel efficiency). FWD cars beat this by turning the engine sideways, now the axles turn parallel to the engine, no redirection of power is needed. The net result ...


1

This is what I did for my 2003 Opel Agila. Firstly, you need an android device. Mine is a Galaxy S4. Firstly, go onto eBay and search for an ELM327 reader, it will come up with lots of OBD-II readers for a few pounds/dollars. Make sure you click the UK Only box, or whatever your country is so you don't have to wait years for shipping. Then choose the price ...


1

The specific answer to your question lies in the BSFC (Brake Specific Fuel Consumption) map for your engine, combined with the desired output. The BSFC map shows how efficiently the engine converts chemical energy to mechanical work at any given condition. Here is an example:



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