Supercharger sizing question

[Greenwood037]

Hello Guy,
I am looking at supercharging my Lancia Scorpion. I am currently running a ported 8v head with stock valves on a 2.0. I have run through some basic math to try to figure the CFM required out of the compressor to achieve a desired boost pressure. Here is what I have:

(target boost +1) x engine displacement x (rpm/2) = CFM required

With those parameters, I get:

(1 bar + 1) x .07 cu ft x (6000 / 2) = 420 CFM to achieve 1 bar overpressure

I know this calculation is fundamentally flawed based on the fact that I will never get 100% of the incoming charge forced into the combustion chamber. I would think that the higher the flow (for example 16v vs 8v) the closer I will be to requiring the 420 cfm from the compressor. I would also think that the higher flowing head would (of course) produce more power, but read a lower boost pressure. Due to the fact that there is less charge left in the intake manifold after each intake valve opening.

What I am looking for is a formula to calculate how much charge will be allowed into the combustion chamber. I would expect that it is possible that a compressor that will produce 1 bar on an 8v 1995cc engine would fall short of producing 1 bar on a 16v engine, while producing more power.

Does all this matter? Should I just go with the smallest blower that will give me the required boost, just based on my crude calculation?

As far as I can tell, so far, the compressor for me would be the Eaton M62. A twin-screw compressor would be better, but I am having trouble finding the compressor map for the only affordable OEM twin-screw I have been able to find.

Thanks for your help, please let me know if I am leaving out any needed information.
Jason Greenwood

[petert]

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