Welcome • User Guide
ToS • Privacy • Canary
Donate • Bugs • License

©2025 Poal.co

560

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?

(post is archived)

You are currently inside a comment thread.
Click here to see all the comments (41).
[–] • 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.

[–] • 0 pt (edited )

I'll try but I do not believe you understand what you're saying.

Boosting does not change the compression ratio. Period. It changes density. Or another way to look at it is air flow.

50000000psi into a 8.5:1 engine is still 8.5:1. It will move a shit ton of air through it, but the compression ratio is unchanged.

Again, what is it you are really trying to figure out? Because the statements in OP is in error, resulting in a position which cannot be resolved.

[–] • 0 pt

Boosting does not change the compression ratio. Period.

The compression ratio is a ratio that the air has been pressurized to, relative to atmospheric conditions. 10:1 compression ratio is the same whether achieved by a piston squeezing air or a compressor raising the pressure in the manifold.

In a cyliner, volume goes down for a given air mass, pressure increases. In a turbo, volume is constant for an increasing air mass, pressure increases. In both cases the pressure increases, that compression ratio above atmospheric can and should be expressed as a combined effective compression ratio. Instead we use the cylinder pressure ratio which must be measured directly.