Supercharger Cfm


safe supercharger cfm = (162)(3.14)(stroke)(bore ÷ 2)2
                                                    compression


Supercharger_123rf

Pictured is a supercharger with 2 carburetors and the air intake on top.


What you do:

Calculate the super charger cfm (cubic feet per minute or ft3/min) your engine can handle.


Factors to consider:

1. Supercharger boost is measured in psi (pounds per square inch or lbs/in2) and determined by how many cfm the supercharger is pushing in compared to how many cfm the engine would normally draw in. Supercharger boost adds pressure to the air, which makes the air denser. Denser air can have more fuel added to it, which will add more power.

maximum supercharger boost in psi = 14.7 psi x supercharger cfm
                                                                         engine cfm

Engine cfm is typically between 500 - 1500. The algorithm to accurately calculate engine cfm is long, so see factor 2 (below) to get an easier set of equations to use.

2. Your engine can only handle a certain cfm from the supercharger before intense heating occurs in the cylinder. In HiPerMath, when the cylinder gets too hot, the engine loses power. In real life, the excessive heat will cause the fuel to detonate when the piston comes up and compresses the mixture. This is bad for the engine and likely to destroy it. The amount of heat in the cylinder can be reduced by reducing the compression. Typical compression ratios for supercharged engines are 7.5:1 or 8:1. The following equations help you determine how many cfm to put out from the supercharger based on compression ratio.

First, calculate the cubic inches of the cylinder when the piston is at tdc (top dead center). The term tdc means the piston is at the top of its travel.

cubic inches at tdc = (3.14)(stroke)(bore / 2)2
                                            compression

heat factor =      supercharger cfm     
                         cubic inches at tdc

If heat factor > 162, your supercharger is beginning to produce significant heat. You can still increase the supercharger cfm past this point, but you will soon begin to lose horsepower. The equation below puts it all together.

safe supercharger cfm = (162)(3.14)(stroke)(bore / 2)2
                                                    compression

3. Weight. The larger the supercharger you have, the more weight is added to the total weight of your car.

The HiPerMath equation is:

supercharger weight = supercharger cfm + 50
                                               10

Supercharger weight includes the belt, pulleys and intake pieces, such as spacers.

A supercharger is driven by the crank, so its cfm is related to rpm (revolutions per minute). There is no lag in boost, like a turbo would have.


Definitions:

cfm = cubic feet per minute = ft3/min
psi = pounds per square inch = lbs/in2
rpm = revolutions per minute