The YS-91AC 4 cycle engine is often cited as significantly more powerful than any other comparable (in cubic capacity) 4-cycle engine. Why is this and how can YS be so confident in their claim?

Well, they claim that the engine is fuel injected as well as supercharged. Let us see if these claims are true. If you were to take the classic descriptions used by the automobile or aero engine manufacturers on their fuel injection and supercharging techniques you may wonder at the truth of YS statement.

The 3 primary ways of supercharging an auto or aero engine are:

• 1. Use a belt driven or electric fan (blower) that increases the density and pressure of air into the engine air intake
  
• 2. Use the exhaust gasses to drive a turbine to get the same effect (this is often referred to as a "Turbocharger)
  
• 3. Cool the air to make it denser, therefore more air molecules per cubic foot, therefore more air molecules into the engine per intake "gulp" (this often called an Intercooler)

First of all let's get some terminology sorted out. When I refer to "Intake" I mean the primary breathing area of the engine - in a carbureted engine this mean the air entering the carburetor. When I say "Inlet" I am referring to the point that the fuel and air, either separately of as a mixture enter the combustion area of the cylinder.

Normalizing the three methods to their very basic function we can easily see that all three end up doing much the same, viz. provide a greater density and/or pressure of air to the engine. With the greater density there are more molecules of air per cubic unit, therefore more fuel per cubic unit can enter the engine at a given mixture ratio. So, if the action of providing this greater density and pressure of air to the "Intake" is the function of supercharging, then the YS is not supercharged. In the YS, the air is sucked in through the carburetor by the vacuum in the crankcase caused by the upward travel of the piston - just like all other non-supercharged model engines.

So, is there a legal case coming up? Is this false advertising? Well definitely "No!" If we revisit what is happening in the "Supercharging" of an engine just one step further and submit that the high pressure/density of air going into the "intake" is a means to an end rather that the end itself then YS can redeem itself. As we said, the reason we offer a higher density and pressure of air to the "intake" is to be able to increase the amount of fuel/mixture getting to the engine. More fuel, more power. In a regular non-supercharged 4 cycle engine, the vacuum that draws the air into the carburetor is also the vacuum the transports the fuel/air mix to the upper cylinder and it does this once every two revolutions of the crankshaft. YS take a different approach. They use the bottom end of the crankcase and the piston travel to first suck in the air and then to pump it out of the carburetor into the "Inlet" manifold (air chamber). A rotary valve connected to the rear of the crankshaft facilitates this. This 2 cycle "Suck/Blow" operation - once for each revolution of the crankshaft - provides the fuel mixture to be presented in higher density and pressure to the "Inlet" manifold (Air Chamber), and therefore into the upper cylinder. The mixture stored in the "Inlet" manifold is the result of two charges per power stroke. This happens even without pressurizing the air "intake". The end product is the same as that for a traditionally supercharged (pressurized air "intake") engine. So is the YS really supercharged. I say Yes!

Fuel injected? Now there's the other question. How can a fuel-injected engine have a carburetor and no fuel injectors? Well, you are thinking in the terms of traditional auto and aero engines again. Don't. YS have been very innovative. The complex auto and aero engines that use fuel injectors do so as a means to an end. Where have we heard that before? By injecting fuel through computer controlled injectors you can easily meter the amount of fuel per power cycle. This leads to more power and better fuel economy. So, instead of applying high-pressure fuel into the air inside the cylinder to create the mixture, the YS engine causes the fuel to still be pressurized but as part of the mixture in the Air Chamber - not in the cylinder. The supercharging effect that we already discussed provides that pressure in the Air Chamber ("Inlet" manifold). We saw that to do this, YS forced the fuel mixture into the manifold (Air Chamber) at crankcase pressure twice per power stroke. The disk valve in the crankcase keeps the pressure in the Air Chamber during the non-power stroke. So the mixing of fuel and air is done before entering the cylinder and twice per power cycle.

So if the purpose of fuel injection on an engine is inject high pressure fuel into the cylinder, then the YS engine is not fuel injected. But since the mixture is injected at high pressure into the cylinder (By virtue of it's "Inlet" manifold pressure) then we could say that the YS engine has "Mixture Injection" rather than fuel injection. So, I pose this question. Is the raw liquid from the tank the fuel or is the mixture of the liquid plus air the fuel? Let's look at one of Webster's entries for "Fuel":

fu·el pron. (fy l)
Something consumed to produce energy, especially:

• A material such as wood, coal, gas, or oil burned to produce heat or power.
  
• Fissionable material used in a nuclear reactor.
  
• Nutritive material metabolized by a living organism; food.

Based on this, I submit, since to produce energy the engine consumes both the liquid and the air, that it is the mixture that constitutes the actual "Fuel".
If so, then YS engines are "Fuel Injected"

The copious amounts of pressurized gasses and fuels inside the YS engine makes you completely understand why the YS 4-cycle engine "O" rings and gaskets must seal perfectly.

One more thing. To assist the drawing-in of the raw liquid fuel into the engine on each revolution, the YS engine requires raw fuel to be supplied at high ppressure. Therefore, the YS engine has a pressurized fuel system that uses crankcase pressure, supplied through a check valve to pressurize the fuel tank. This ensures the "On-demand" fuel system on which the YS engine relies.

So, 30% - 35% more power than more traditional 4-cycle engines? I believe it. No lawsuits coming from me.