(US Patent #5,007,387)

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Valve Area Comparison

1.60"  Ex. Area is 2.01square in.

2-1.40" Ex. Area is 2.99 sq. in.

36%

more valve area

Why 4 Valves

Check out some Flow Charts

Intake valve flow and horsepower

This huge valve area can be used with no loss of low end torque. This is because the ports can be made with the same cross sectional area as a 2 valve head. (the CC’s of the runners that is commonly used). This means that the port will have the same velocity as a 2 valve head, hence the same low end torque. Similar to a long hallway that is the same size,  but with 2 big doors at the end instead of 1. The hallway will get up to high flow earlier  because the area of the doors opening can reach the full flow of the hallway much faster. So with each opening and closing of the doors, since they get up to the large area earlier are flowing the full capacity of the hallway for a longer period of time. (Meaning more crankshaft degrees of high intake port flow). This gives us a higher overall average velocity,  and this fills the cylinder with more air fuel mixture on the intake stroke and makes more horsepower, since more air fuel mixture in, means more to explode, a higher cylinder pressure to push the piston down and more horsepower.

More advanced explanation of curtain flow area.

Note: This section is more advanced, for the engineer.

Curtain flow area defined, is the (perimeter of the valve) X  (the height of the lift). This is the actual flow area (the actual flow window) that the air sees. The band of area around the lifted valve to seat.

INTAKE:

1)      A 2.02” intake valve X .600” lift has a curtain flow area of: (2.02”) X (3.14) X (.600)= 3.81 sq. in.

2)      2: intake valves at 1.65” each X .600” lift has a curtain flow area of:  (1.65”x 2 valves) X (3.14) X (.600)= 6.22 sq. in. 

What this huge curtain area increase does is open the flow window of the air much faster and earlier in the valve lift cycle. Even if we take two heads, a regular 2 valve head and a 4 valve head. They are both ported for 300 CFM of intake flow. (by the way none of our heads flow this little) The 4 valve will still make substantially more horsepower and torque. Why? Because with the intakes reaching high flow much earlier, (for example most of the 4 valve heads flow 50% more air at only .050” lift than an aluminum 2 valve head) there are many more crankshaft degrees of really high intake flow to more fully fill the cylinder. The same peak port velocity, but a higher average port velocity because it starts earlier and ends later.        

This can be shown graphically when the two intake flow graphs are overlaid on the same page. The area under the curve difference shows how this phenomenon  works. This difference in the way the two different types of heads work must be understood to fully comprehend the performance gain.  

This is the main reason for the difference in performance over the standard head.

EXHAUST:

1) A 1.6” exhaust valve has a curtain flow area of: 1.6” X 3.14 X .600” lift = 3.01 sq in.

2) 2 exhaust valves at 1.40” each has a curtain flow area of: (1.40” X 2 valves) X (3.14) X (.600” lift) = 5.28 sq in.

What this increase in exhaust curtain flow area does is enables the cylinder to be evacuated with less energy from the piston needing to push out the spent gases. This less back pressure allows the cylinder to be more fully evacuated, leaving less hot dead no oxygen gases to take up precious space that the new incoming fresh charge can occupy. This works well in normally aspirated motors, but is further exemplified in blown or nitrous motors.

This is why the 4 valve heads have nearly twice the exhaust sound than 2 valve heads. The sudden hot gases opening to atmosphere, makes the largest sudden pressure differentiation and the most noise. This is why the Small Block 32 valve sounds like a KB Hemi.

Exhaust valve flow and horsepower

On the exhaust stroke this faster area opening of the doors means that the superheated exhaust gases are taking less pressure to push out the ports, which means the piston doesn’t need to push as hard against the gases. And taking less crankshaft horsepower to evacuate the cylinder. Meaning more crankshaft horsepower available. There is also a more complete evacuation of  the exhaust gases, meaning a cleaner chamber with no contamination of non oxygen carrying gases to just take up useless space on the next intake cycle.   

Combustion Chamber Design

The 4 valve per cylinder head incorporates the most modern of combustion chamber designs. The centrally located spark plug offers the shortest flame front to any spot in the cylinder bore. The 360 degree squish band accelerates all of the air on the compression stroke to the center,  making the fastest most completely burning chamber of all. Making the motor less prone to detonation. This is why the 4 valve head can run half a ratio higher on pump street gas than any 2 valve head. Another advantage is the 2 exhaust valves, even though combined have much more area than one valve, do it with 2 smaller valves. They run cooler because of more cooling up the same size valve stems. This has less tendency to glow red and pre-ignite the mixture.

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