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Like wtf bro, if you have a piston that's doing 12:1 compression ratio, that's a calculation based on volume. If you compress the air with a compressor, that pressure ratio is factored into the cylinder with the piston at BDC. Where is the calculation for the effective compression ratio where boost is added to the compression ratio at TDC? It doesn't exist, it's a conspiracy man. I mean what is the functional relationship? Is it additive? 14 psi of boost = 2:1 compression ratio, and an engine with a 10:1 geometric compression ratio now has an effective 12:1 geometric compression ratio? That can't be right, because then it would just be easier to use an 12:1 piston and save all the turbo plumbing. Is it multiplicative? 10x2=20? So a 10:1 CR piston with a 2:1 compression ratio from a compressor would effectively have 20:1 compression ratio? Or is it some other non-linear function that can only be gleamed through experimentation?

Like wtf bro, if you have a piston that's doing 12:1 compression ratio, that's a calculation based on volume. If you compress the air with a compressor, that pressure ratio is factored into the cylinder with the piston at BDC. Where is the calculation for the effective compression ratio where boost is added to the compression ratio at TDC? It doesn't exist, it's a conspiracy man. I mean what is the functional relationship? Is it additive? 14 psi of boost = 2:1 compression ratio, and an engine with a 10:1 geometric compression ratio now has an effective 12:1 geometric compression ratio? That can't be right, because then it would just be easier to use an 12:1 piston and save all the turbo plumbing. Is it multiplicative? 10x2=20? So a 10:1 CR piston with a 2:1 compression ratio from a compressor would effectively have 20:1 compression ratio? Or is it some other non-linear function that can only be gleamed through experimentation?

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[–] • 2 pts

You are confused. Compression ratio is the cylinder volume of BDC to TDC. This ratio effects efficiency, not "effectiveness."

Boost is the measure of increase over atmospheric pressure. It doesn't change volumetric compression ratio. As it changes charge density and not physical volume on either end of the stroke/cycle.

[–] • 0 pt

Compression pressure is both the geometric and manifold pressure, this means that both the geometric and atmospheric compression ratios combine to arrive at the cylinder pressure at TDC. Which means there is an effective compression ratio. Compression ratio is compression ratio, it has nothing to do with efficiency and everything to do with the compression of the air.

[–] • 0 pt (edited )

It doesn't change volumetric compression ratio.

I know, I said that, but the density increase increases the effective cylinder pressure, in the same way that the piston itself increases the cylinder pressure as it moves to TDC. So what then becomes the effective compression ratio when boost is factored in? With an axial jet engine the compression ratio is straight forward, the pressure tap reads 147psi at the end of the second spool compressor, that's a 10:1 compression ratio.

With a piston engine, you have volumetric compression of the air in the cylinder and density compression with the turbo. Both are physically compressing the air at a certain ratio, the two events do not exist in isolation, and combine to produce an effective cylinder pressure.

[–] • 1 pt

the pressure tap is psia?

[–] • 0 pt

Ask what you're trying to accomplish. Because you're stating things which are incorrect and asserting I'm the one in error.

[–] • 0 pt

What part is incorrect? What I'm trying to accomplish is stated in the OP.