awesome formulae!:bigsmile:Try this:
Boost (psi) = (PR x 14.7 x V / C/2 ) - 14.7 - I
PR is pulley ratio, crank pulley diameter divided by drive pulley diameter.
14.7 is the pressure of the air we live in, we don't live in a vacuum, we live in 14.7 psi.
V is the volume of your blower for one rotation.
C is capacity of the engine in cc
C/2 is C divided by 2 - because for one rotation, a four stroke engine is only half way through a complete cycle. When the piston is up the top and starts going down, air and fuel go in, then it gets to the bottom and goes back up and compresses the mixture. That's one rotation. Then the spark plug ignites the mixture and it starts to go down again, it gets to the bottom and then goes back up again pushing the burnt mixture out the exhaust valve and returns to the top to start over again. That's two rotations.
I (capital "i") is an allowance for boost lost due to valve overlap. All engines have valve overlap; the intake valve opens before the exhaust valve closes - the incoming fresh air and fuel pushes out the last of the burnt exhaust gases.. The allowance is around 5% boost lost for every 10 degrees of overlap.