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🚗 | [Test drive] The new MR Wagon targeting young people was finished to satisfy even veterans [10 years ...


[Test drive] The new MR Wagon targeting young people was finished to satisfy even veterans [10 years ...

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Naturally aspirated engine cars also blow up lightly over the entire area, generating thick torque from the low rev range.

It is often said that "10 years ago", but about 10 years ago, there was a growing tendency for cars to emphasize the environment and safety.Yeah ... → Continue reading

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Natural aspiration

Natural aspirationWhat is Qiongqi?Turbocharger,SuperchargerSuch asSuperchargerWithoutAtmospheric pressureInhale into the cylinder withengineOne of the methods of distinguishing.NA(NA: Natural Aspiration)No superchargingOr sometimes called "non-turbo"[1].. EspeciallyAutomobileIn this way, the engine that does not have a superchargerNaturally aspirated engineCalled.This section describes the naturally aspirated engine in this automobile engine.


Originally, all engines, not just automobiles, were naturally aspirated, so the name "naturally aspirated", which was born after superchargers began to spread in automobiles, was an opposition to engines with superchargers.Retro NimIs.Naturally aspirated engines have become the mainstream gasoline engines for general automobiles with small to medium displacements, especially in terms of low fuel consumption and low emissions.For a car with a large displacement, it is difficult to balance cost and performance,sports car,Super carExcept for someTurbo engineIs the mainstream.


The characteristics of naturally aspirated engines, which are generally referred to, are that they do not have the advantages of superchargers, just as the origin of the word was reflected in the antonym of supercharged engines. It does not have the disadvantages of a turbocharger.

Generally, a naturally aspirated engine with the same displacement has a simpler structure and is lighter than an engine with a supercharger.This requires a structure in which an engine with a supercharger not only has a supercharger, but also has an oil pipeline for cooling / lubricating the supercharger, and also brings together the exhaust system and the intake system. It depends.In addition, since the supercharged engine is subjected to a huge amount of pressure more than the naturally aspirated engine, the block needs to be sturdy, and the engine weight inevitably increases due to the increase in strength.

Naturally aspirated engines tend to have high thermal efficiency and good fuel economy.However,dieselDirect injectionThis does not apply to state-of-the-art engines, including turbochargers.This is because moderate exhaust supercharging should increase thermal efficiency in principle in terms of regaining exhaust energy.In addition, the tendency for good fuel economy is largely due to the lightness of the engine and the light body (not necessarily sturdy) due to its low output.

Naturally aspirated engines generate less heat than supercharged engines.A supercharged engine can burn a large amount of fuel with compressed air in a combustion chamber having the same volume, so that heat generation is high.This reduces thermal efficiency.This is because the thermal efficiency is basically better (larger) as the temperature difference between the low temperature and the high temperature is wide.

The compression ratio is higher than that of supercharged engines, and it is around 7 for supercharged gasoline engines, while it often has 9 or more for naturally aspirated engines.A low compression ratio also reduces thermal efficiency.This low compression ratio is also a measure to avoid knocking due to high temperature (in a diesel engine, the compression ratio is rarely lowered even with a supercharger, which increases the thermal efficiency of the diesel engine).

The naturally aspirated engine is a high-speed type.In a supercharged engine, intake can be forced.However, at the same time, when the supercharger uses the exhaust gas to compress the intake air, it deprives the flow velocity of the exhaust gas.This creates a state in which the burned gas is not exhausted well, that is, the exhaust efficiency is reduced.If the exhaust efficiency decreases, the resistance received from the exhaust gas increases when the cylinder rises in the exhaust process.That is, a part of the output of the engine is consumed due to the exhaust of gas.Since this effect becomes more remarkable in the region where the piston speed is high at high rpm, the engine with a supercharger tends to reduce the torque in the high rpm region.Naturally aspirated does not have this property, so it exerts torque without slack even at high rpm.Famous as a representative of high-speed NA engineHonda・,Nissan VQ37VHREtc.

The naturally aspirated engine has a flat output distribution.In a supercharged engine, a huge amount of torque is generated after the inside of the supercharger rotates and supercharging is started.Therefore, the torque distribution forms a steep peak in combination with the torque decrease at high rotation speed.This is often referred to as the "doccan turbo" and expresses the difficulty of adjusting the accelerator.Naturally aspirated engines do not have that characteristic.

Naturally aspirated enginethrottle(Accelerator) Excellent output response to operation.This is because the supercharger does not intervene in the intake air.If a supercharger intervenes, it takes a moment for the inside of the supercharger to rotate when the accelerator is depressed.It is similar to the fact that the turbocharger has a moment of inertia.The advantages of this responsive property are not small in terms of ease of driving and maneuverability.In addition to the flat torque characteristics mentioned above, it can be said that the naturally aspirated engine, which is often one step inferior to the supercharged engine in terms of absolute output, has gained strong support in sporty cars and GT cars.


The naturally aspirated engine responds to the accelerator quickly and linearly (increasing in proportion to the amount of depression), but on the other hand, it is the same.DisplacementIt is less powerful than the supercharged engine.Therefore, various measures were considered to increase the output.

As a method for increasing the output, add a supercharger andMechatuneThere is.With the addition of a supercharger, it will have the characteristics of a supercharged engine.Select this if you simply want to focus on output.If the same model car has a supercharged engine,To replace it with that engine, Added supercharger as after-parts[2]I have something to do.Mecha tunes are expensive and are sometimes said to cost 1 yen per horsepower (it costs 1 yen to increase one horsepower).Means are also limited, but naturally aspirated properties can be preserved or enhanced.But in the world of street tune,VVTEtc.Variable valve mechanismIn some cases, such a mechanism is removed.

Practical high-power engine with naturally aspirated engine

The output (especially horsepower) can be increased by the variable valve timing mechanism (lift mechanism).Automakers are actively adopting it.Honda's representative oneVTEC(VTEC) And ToyotaVVTs(Including derivative versions of VVTL-i and Dual VVT-i, VVT-iE, Dual VVT-iE), NissanNEO VVL, MitsubishiMIVEC(Including derivative version of MIVEC-MD).


  1. ^ When describing, it may be written as "N / A" or "NA".
  2. ^ In the case of a turbocharger, such a retrofit is "ン ル ト オ ンIt is called "turbo" or "bolt-on turbocharger", and in the case of a supercharger, it is called "bolt-on supercharger".

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