So how does it all work
this is  physics
in a simple explanation

This article is very contentious as its people who believe air is sucked into a engine and those who know air travels at 343 meters per second into a vacuum.
Laws of physics fact,  
When the downstream pressure (the vacuum) is very low compared to the upstream pressure (the air), the flow becomes "choked," meaning the flow rate is limited by the speed of sound and doesn't increase further even with a larger pressure difference.
Factors Affecting Flow Rate:
The actual amount of time it takes for air to fill a vacuum depends on factors such as the size of the chamber, the pressure of the chamber, and the size of the opening through which the air flows.
Speed of sound in air:
The speed of sound in air is approximately 343 meters per second (or 1234 Kilometres per second) at room temperature.
What does it mean air travels into a vacuum, in depends on several variables many explained by physics, but air travelling into a vacuum works differently as its not restricted by the same things when the air is sucked in, mainly the inlet restrictions.
A more detailed explanation
When air rushes into a vacuum, the speed is determined by the speed of sound at the prevailing temperature and pressure, not by any "sucking" action of the vacuum itself.
Here's a more detailed explanation:
Pressure Difference Drives Flow:
Air flows from an area of higher pressure to an area of lower pressure, not the other way around.
Vacuum Doesn't "Suck":
A vacuum doesn't have the ability to pull air in; rather, it's the surrounding air pressure that pushes air into the vacuum.
Speed of Sound as a Limit:
The air molecules entering the vacuum will move at approximately the speed of sound at the current temperature and pressure.
Choked Flow:
When the downstream pressure (the vacuum) is very low compared to the upstream pressure (the air), the flow becomes "choked," meaning the flow rate is limited by the speed of sound and doesn't increase further even with a larger pressure difference.
Factors Affecting Flow Rate:
The actual amount of time it takes for air to fill a vacuum depends on factors such as the size of the chamber, the pressure of the chamber, and the size of the opening through which the air flows.
Speed of sound in air:
The speed of sound in air is approximately 343 meters per second (or 1234 Kilometres per second) at room temperature.  

  Michael Fowler Professor of Physics

I must say what a vacuum is, when the air pressure drops below 14.7 pound per square inch, so when a piston goes down in a cylinder it creates a difference in air pressure between the cylinder pressure and the pressure outside the engine, but because air travels so fast that difference in air pressure in the cylinder will never get much under 14.7 lbs per sqr inch but its still a vacuum of 1 lbs a sqr inch, but at 10,500 rpm a 60cc stroke the piston travels at 12 mrs per second but at 10500 RPM the piston speed is 23 m/s  at this speed is the max the air can travel before it takes the air longer than the piston speed resulting in the piston travelling faster than the air resulting a loss of air fuel mixture, at 11,000 rpm the air pressure will be 13.23 lbs per sqr inch which is a loss of 13% of power and it continues to lose power the higher the rpm, at 13,000 its has a loss of 78% due to air fuels starvation, but air travels at 343 m/s. 
What can make a huge difference in air speed if all you require is 10,500 rpm then you can play around with the air speed, at low revs we know the cylinder is going to be filled so by reducing the inlet size by 75% and the revs 75% 2,500 rpm the air can then travel at 343 m/s 4 times the speed and much better air fuel atomisation giving more power, the ideal system would be a air restrictor between the inlet manifold and the cylinder head that can vary the restriction from semi closed at low rpm to no restriction at high rpm, this method would give max BHP and torque through the whole rev range and fuel efficiency.
What this is telling you is the speed of air entering the cylinder, the higher the speed the better to fuel air mixture atomisation, better atomisation more power. You can also experiment with inlet valve opening time, the later the faster the air flow. As a guide go to car-calc and calculate and enter the cc of one cylinder and it will tell you what you max rpm is before the engine has to start sucking air in, then use this as a guide.
Because air is relatively incompressible at low speeds, it cannot simply pile up in a narrow passage; therefore, its speed must increase to pass the same amount of air through a smaller opening (Area ×cross ×Velocity = Constant).
Air travels at 343 m/s into a vacuum, that like a high depression flowing in to a low depression we call it wind, but in a engine we are looking at flow rates at their maximum, so if air has to travel through an aperture and there is a vacuum at the other side then the air speed will be 343 m/s.
The maximum air can travel is when a plane goes faster than 1234 Kilometres  per hour, it splits the air creating a vacuum and as the forces are so great to fill that vacuum the collision speed of the air is 686 M/s per second and when the gap is closed it causes a sonic boom.
At low RPM a small valve is better as the speed of the air is faster giving better atomisation more power leading up to a large valve at high RPM as it requires volume. The perfect system would be a variable size inlet, small for low RPM to large for high RPM optimising atomisation for more power over a larger RPM range. These act in a different way to the butterfly, at low RPM the aperture in the inlet would be small and the butterfly would be fully open.
The perfect adjustable air valve would be similar to what's in a camera, but to trial it cut a slot in the inlet manifold cylinder head side to take a large washer, starting with a washer with a small hole 20mm if the port size is 40mm working up to fully open, theoretically when you get the fuel mixture correct at say 2,500 rpm everything points at increased torque and BHP. Another way is to ajust the camshaft timing so valve opens full at 135 degree ATDC, this will have the same effect as reduced intake
  There is a test you can do to see air working at atmospheric pressure, with piston fitted and the cylinder head fitted with valves closed try to pull the piston to the bottom of the bore, you will find its nearly impossible and your only pulling against 14.7 per square inch of air pressure normal atmospheric pressure.


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Air pressure explained
Air absolutely has mass and weight because it's made of molecules (like nitrogen, oxygen, water vapor) that take up space and are pulled down by gravity, even though it seems weightless because it's so spread out (low density), but you can prove it by weighing a deflated balloon versus an inflated one, or a container with and without air. The total mass of Earth's atmosphere is enormous, around 5.15 quadrillion tonnes, demonstrating air's significant mass.
Matter: Air is matter, meaning it has mass and occupies volume.
Composition: It's a mixture of gases, primarily nitrogen (78%) and oxygen (21%), all made of molecules with mass.
Density: Air has low density (about 1.29 kg/m³ at sea level), making its mass hard to notice, but it's still there.
Proof: An inflated balloon weighs more than a deflated one, and a vacuum chamber shows a measurable weight difference when air is removed, proving air has mass.
Atmospheric Pressure: Because air has mass, gravity pulls it down, creating atmospheric pressure that pushes on everything.
For engine builders we use PSI pounds per square inch 14.7 psi, we also work with Bar which is 14.5 psi
What I am trying to get across how air has body and can travel at very high speeds, but as we think we cant feel it or weigh it we tend to overlook the power of air.
The two most common units for measuring air pressure are Millibars (mb) used heavily in meteorology, and Kilopascals (kpa) the standard SI unit, often alongside inches of mercury (inhg) U.S. weather reports, with atmospheres (atm) and pounds per square inch (psi) also frequently seen, especially for general or technical
An American university did a experiment, take a meter long tube place a ping pong ball in the tube box tape both ends then suck out the air, the prick the end and the ball comes out the other end at 375 MPH, that is the power of air.
When a compressor explodes, if you use high speed recording the tank doest destroy its self when it bursts, its after the air has been expelled the air then fills the vacuum at 343 m/s that destroys the tank.
So how does it all work
Its  laws of physics in a simple explanation
Air travels into a vacuum at 343 m/s or 1234 kilometres per hour into a vacuum, so air is not sucked into a engine its pushed in as it has to fill the vacuum.
A piston descending in a cylinder creates a vacuum and as the piston is only travelling at 25 meters per second the air has more than enough time to charge the cylinder, it only when the piston speed + volume does it stop and then relies on suction.
We can work out the RPM of that cylinder which is determined by piston cubic capacity, lets say your cubic capacity is 300cc per cylinder.
To work out maximum RPM a engine will run at we only need to look at one cylinder and at 11,500rpm
my avenger is 326cc which will rev to 10,500 before it has to suck in air, which can be done and my car-calc program will tell you a % in loss of power over max revs over the law of physics.
The fact air will find its way into the cylinder you can start playing around with valve size, inlet size and exhaust size. By fitting a smaller inlet valve means the air speed over the valve has to be faster to fill the cylinder in the given time, but this means much better air to fuel atomization giving more power at lower revs but will still reach the max rpm.
One of the best engines to exploit this was the 60s GT40 when they enlarged the cubic capacity they reduced the valve size, this gave the car more torque but still revved to its max which was much less than a Ferrari  V12 revving to 12,000rpm but little torque, as a driver i would rather have torque in a 24 hour race, a winner every time in my book.
So to design your engine you only need to develop one cylinder, say 300cc reving to 11,500rpm once you have developed it to its max then you can add on cylinders depending on what overall cubic capacity you want, 4 cylinders = 1200cc 8 cylinders = 2,4000cc and 12 cylinders = 3,600cc and all will rev to 11,500rpm.
Take my engine producing 180bhp from a 1300cc engine but taking the cubic capacity to 2,600cc doesnt mean it will still rev to 11,500 rpm it wont it will be 5,500rpm but make it 60cc per cylinder 8 cylinder total 2589cc will rev to 10,500rpm.
The reason it works is a Professor told me it would work and i believed him, and worked on it until it did what he said, so its all about belief.








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