why do some smaller engines have lower gas mileage than some larger engines?
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Modern turbo engines are a great example of this. If you drive them like the factory tester going for the EPA certification numbers then they get good mileage. But take that same car out into the real world where everyone drives like an idiot, get on the boost and it drinks fuel like mad.
Because to get the power out, you still need to put the fuel in. Sometimes over-boosting small engines makes it worse than that bigger lazy engine that never breaks a sweat.
That said, peak engine efficiency at a steady cruise is somewhere around 70% load. So theoretically the small engine is better.
Basically, large engines always have an advantage when it comes to peak efficiency, but an engine has to be built to match a load. Engines perform best at lower RPM but almost max. throttle. If you have a big engine giving 200 HP at low RPM and full throttle and a smaller engine giving 200 HP at redline RPM and full throttle, the small engine will be less efficient, and because it still puts out the same power, will consume more fuel.
Take a small person and a muscular person as an example and have them move multiple 25lbs bags of sand, one by one repeatedly.
Small person can do the same lifting capacity as the larger but will require more energy/effort to do the work.
The larger person will use less energy, and require less effort to do the same amount of work.
Take a small person and a muscular person as an example and have them move multiple 25lbs bags of sand, one by one repeatedly.
Small person can do the same lifting capacity as the larger but will require more energy/effort to do the work.
The larger person will use less energy, and require less effort to do the same amount of work.
Engines don’t have a gas mileage.
Vehicles do.
And vehicles can, for example, vary significantly in weight, unrelated to the engine.
Engines don’t have a gas mileage.
Vehicles do.
And vehicles can, for example, vary significantly in weight, unrelated to the engine.
It takes energy to cause a piston to move, and it stops at each end of each stroke. Every time you move that piston, you expend energy just driving it. The faster you move it, the more energy you waste per stroke. The more frequently you move it, the more energy you waste. This is (part of) “pumping loss”. Broadly speaking, this is the energy the engine consumes within itself in order to be able to produce a useful output.
To develop a net 200HP at the output shaft, a small engine might have to turn 6000 RPM. The total power produced might be closer to 300HP, but 100 of that is wasted just moving the engine’s internal components. This engine, at this 200HP output, will be extremely inefficient.
A larger engine might produce 200HP out at 900RPM, with just 10HP in pumping losses. This engine, at this output, will be very efficient.
If you only need 10HP, though, that second engine might need to turn at 600RPM, with 9HP lost to pumping. The first engine might be able to achieve it at 900RPM, with 1HP lost to pumping. At this lower output, the smaller engine will be much more efficient than the larger.
The key to efficiency is matching your engine’s output to your load; or your load to the engine’s output. The greater the mismatch between optimal output and actual load, the less efficiently the engine will operate.
It takes energy to cause a piston to move, and it stops at each end of each stroke. Every time you move that piston, you expend energy just driving it. The faster you move it, the more energy you waste per stroke. The more frequently you move it, the more energy you waste. This is (part of) “pumping loss”. Broadly speaking, this is the energy the engine consumes within itself in order to be able to produce a useful output.
To develop a net 200HP at the output shaft, a small engine might have to turn 6000 RPM. The total power produced might be closer to 300HP, but 100 of that is wasted just moving the engine’s internal components. This engine, at this 200HP output, will be extremely inefficient.
A larger engine might produce 200HP out at 900RPM, with just 10HP in pumping losses. This engine, at this output, will be very efficient.
If you only need 10HP, though, that second engine might need to turn at 600RPM, with 9HP lost to pumping. The first engine might be able to achieve it at 900RPM, with 1HP lost to pumping. At this lower output, the smaller engine will be much more efficient than the larger.
The key to efficiency is matching your engine’s output to your load; or your load to the engine’s output. The greater the mismatch between optimal output and actual load, the less efficiently the engine will operate.
There are engine performance curves, if you run the engine outside its “sweet spot” it will degrade in efficiency and therefore have degrading fuel economy.
Each engine has a specific performance curve which is translated into manufacturer recommended operating procedures.
There are engine performance curves, if you run the engine outside its “sweet spot” it will degrade in efficiency and therefore have degrading fuel economy.
Each engine has a specific performance curve which is translated into manufacturer recommended operating procedures.
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