How to calculate air flow?

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Is this right?

I use ((130cid*7000rpm*0.5*0.9ve)/25043))*2.5pressure ratio=40.8 lb/min

How much this is in cfm? 500-550.

I use american units because all the compressor maps are made for lbs/min.

550cfm is about 15500liters per minute.
Now i had to calculate airspeed at intercooler tubing.
If i had 60mm,63mm or a 76mm inner diameter ic tubing, how fast air flows in tubing at 15500liters per minute flow rate?

My math skills stops right here!

If flow rate exceeds mach 0.4 flow resistance will grow very fast, and if charge pipes are too big flow goes from laminar to turbulentic.

I figured out that in my application max airspeed is something about 0.24-0.25mach which is very good, this is with 60mm tubing.
I found a chart in the internet.

but it would be nice to know how that is calculated!

If someone knows how this is calculated, please put the formulas there!

Hi, assuming 76mm tube,

15500l/s = 15,5m^3/min = 0,258m^3/s
cross sectional area of tube = 1/4*pi*D^2 = 0,25*3,14*0,076^2 = 0,00453m^2

Volumetric flow / Area = Velocity, so: 0,258/0,00453 = 57,0 m/s

Speed of sound in air = 343m/s at 20 degrees c.

Mach = Speed of medium / speed of sound in medium = 57,0/343 = 0,17

Sjeng said:

Hi, assuming 76mm tube,

15500l/s = 15,5m^3/min = 0,258m^3/s
cross sectional area of tube = 1/4*pi*D^2 = 0,25*3,14*0,076^2 = 0,00453m^2

Volumetric flow / Area = Velocity, so: 0,258/0,00453 = 57,0 m/s

Speed of sound in air = 343m/s at 20 degrees c.

Mach = Speed of medium / speed of sound in medium = 57,0/343 = 0,17

Click to expand...

Thank you very much!

I just calculated that 60mm pipe has max airspeed of 0.265mach.

That is just below 0.3mach, which is good, but i think that i put a 2.5" piping so i can crank the boost up and even then max airspeed is below 0.4mach which is desired goal.