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To this day, most of the licensed drivers in existence have at least had contact with a naturally aspirated engine during their driving school days – but perhaps most people never care.
This oldest, most primitive, and simplest type of engine has been born almost with the car for more than a hundred years. Whether it is the oil crisis in the 70s, or the popularization of turbines in the new century, or the trend of new energy today, it has not completely driven the self-priming engine out of history.
Even, as 2022 approaches, there are still manufacturers who continue to work on naturally aspirated engines.
Porsche has just come up with the performance ceiling of the 718 series, using the 4.0L self-priming engine on the 911 GT3, and it will be sold domestically; Ferrari's latest limited model, the Daytona SP3, uses the V12 self-priming and ignores all hybrid systems; Toyota and Subaru continue to cooperate to create a new generation of 86/BRZ, adhering to natural suction and increasing the exhaust volume from 2.0L to 2.4L against the trend...
718 GT4 RS sold for 1.578 million yuan, don't be too expensive, this may be the last and cheapest high-performance naturally aspirated car that can be bought in China. For these "retrogrades", of course, feelings are on the one hand, but without some new things that are different from driving school cars, feelings alone are not enough to allow them to survive the horsepower inflation of turbines and motors.
As the name suggests, the air required for combustion inside the engine is naturally "pushed" into the cylinder by atmospheric pressure, without any help. The internal combustion engine was invented in the beginning of this way, and it will only be done this way, and later everyone came up with a variety of pressurized "crooked ideas" to increase the intake of air.
For self-priming engines, and in the past era of self-priming, when supercharging was not common, the intake system is critical to the performance of an engine. Everyone knows that displacement plays a decisive role, so how can there be a difference between the output of the engine with similar displacement?
For self-priming engines that pursue extreme performance, the variable air intake system is a must-have weapon against the supercharging camp.
Porsche's variable intake manifold
When the engine is running under different working conditions, the characteristics of the air that need to be sucked in are different: at low speeds, it needs to be sufficient and long, and the intake line is best "fine water and long flow"; at high speed, it needs to be fast and powerful, requiring the intake line to be short and direct. In the conventional fixed intake system, the internal intake line is naturally fixed and unchanged, which is a contradiction.
An engine with complete performance must have better performance in various working conditions. If the intake system is immutable, if you take care of this head, you will inevitably lose that head, and eventually you will need to make a trade-off between engineers. Many times, car design is a trade-off between "raising the limit" and "guaranteeing the process", so the real limit is often based on new technologies to "liberate" other restrictions.
CVVT, VVT, VVL and other technologies often heard in the early years are the changeable improvements to the gas distribution mechanism such as camshafts, which are limited to the intake valve exhaust valve above the cylinder. These technologies are becoming more widespread today (and not limited to self-priming), and for self-priming engines with higher pursuits, it is necessary to make a big move, variable intake manifold.
A type of variable intake air, adjust the central valve to change the length of the intake path
Porsche uses variable intake manifolds with multiple resonant valves in its self-priming engine. Under preset operating conditions, the path of air into the cylinder can be selected and varied by the combination of opening and closing valves. At low speeds, allow air to flow over longer distances to reach the cylinder, and when high speeds require a lot of air, adjust the valve to use a short intake path.
The variable intake manifold allows the engine to have a more comprehensive torque output in a wider rpm range, the so-called "improved torque curve". Since the maximum engine power is related to the torque at high speeds, the limit output is indirectly increased. In fact, many of the "variable" in the engine are to achieve "balance", because the other side of "balance" is always to make "high" can be "higher".
Ferrari is also a big fan of variable intake manifolds, and the bright red "box" above the engine is a complex intake system. The internal moving structure can change the length-to-diameter ratio of the intake manifold, helping to shorten the intake manifold at high speeds and vice versa at low speeds. Such a variable intake air makes the self-priming engine have high output in the speed range of nearly 10,000 revolutions, and makes full use of the high speed to improve the power limit.
The 5.5-liter self-priming LT6 engine mounted on the Chevrolet Corvette Z06 has a pressure regulating chamber for each of the two exhaust cylinders, and three valves are also arranged in the middle, which can also play a variable intake manifold effect with the fluctuation effect of the intake and exhaust of each cylinder.
The naturally aspirated engine's initiative to improve intake efficiency is also reflected in the application of ITB's independent throttles.
Most civilian cars will only have one throttle, which is what we call "throttle" every day, which directly controls the power output of the vehicle. But one throttle controls multiple cylinders, meaning it must be away from the gas gate. This distance makes it a time difference between the throttles to quickly press down when the air reaches the cylinder.
The solution is simple and crude: install a separate throttle (ITB) for each cylinder. Each command of the throttle is issued directly to the cylinder door (valve), and it can no longer rely on the distance between the throttle and the valve, which can be described as a government order in the engine to the grass-roots level, which greatly improves the response speed of the power.
Independent throttles that often appear in racing cars and movies
Sound wave is a big difference between natural aspirating and turbocharged engines, because the turbocharged engine has more supercharger compressors on the intake path, and engine noise is no longer easy to emanate from the intake side, and you will find that today's turbocharged cars emphasize the so-called "cannon sound" of exhaust more.
The sound wave of the self-priming engine can be transmitted from both sides of the intake and exhaust without hindrance, and the cavity design with the pressure stabilization chamber can also improve the tone and bring more attractive sound waves (such as LFA). The Porsche 718 GT4 RS, an extreme street car focused on track driving, featured the engine intake at the rear of the unique side windows, which brought the engine sound closer to the driver's ears.
The 718 GT4 RS has a very special intake arrangement
The dispute between the turbine and the self-suction is a century of debate in the automotive circle. The small displacement turbines that are now spread across the market give the answer, and the arrival of electrification makes this answer instantly meaningless.
However, whether it is the entire fuel vehicle, or the refinement to the self-priming engine, it still has its irreplaceable characteristics and advantages. For some driver-focused performance machines, there is no substitute for self-priming engines to bring fast power response, and hybridization and electrification can bring similar effects at a higher cost of weight.
So even if there is no trace of possibility of becoming the mainstream, there is still interest for energy, driving the self-priming engine to continue to develop towards the extreme.