I have a question about calculating compression ratios under forced induction.
#1
Staging Lane
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I have a question about calculating compression ratios under forced induction.
I have been trying to understand how to calculate compression ratios under forced induction conditions and dont seem to be getting anywhere. I understand that a compression ratio is the (volume of the cylinder at BTC)/(volume of the cylinder at TDC). What I was wondering and hoping someone in this forum could explain to me was how boosted applications effect this.
For example, say you have a car boosted to 1 bar (2x atmospheric pressure in the cylinder, right?) and with a compression ratio in the engine of 9 to 1. What does the compression ratio become? I dont know if this is the case but if doubling the pressure doubles to compression ratio wouldnt you end up with 18 to 1 compression? That seems way to high for a gasoline engine.
If someone could straighten me out here I would greatly appreciate it.
Thanks
Rob
For example, say you have a car boosted to 1 bar (2x atmospheric pressure in the cylinder, right?) and with a compression ratio in the engine of 9 to 1. What does the compression ratio become? I dont know if this is the case but if doubling the pressure doubles to compression ratio wouldnt you end up with 18 to 1 compression? That seems way to high for a gasoline engine.
If someone could straighten me out here I would greatly appreciate it.
Thanks
Rob
#2
FormerVendor
This is the equation for determining "effective compression ratio"
((boost psi / 14.7) + 1) x static compression = effective compression
Here is how it breaks down on my engine.
(( 19 / 14.7) +1) x 9.2 = 21.09
Damn, I'm only running a 50/50 mix of 93 and 110 for an effective 21-1 compression ratio
IMHO calculating the effective compression ratio is completely worthless.
Basically, I base compression ratio and cam specs on desired power output and fuel octane. (other things like intercooling, vehicle weight, intended use (load), engine type, bore size, etc, etc, must also be taken into consideration when putting together a combination.)
((boost psi / 14.7) + 1) x static compression = effective compression
Here is how it breaks down on my engine.
(( 19 / 14.7) +1) x 9.2 = 21.09
Damn, I'm only running a 50/50 mix of 93 and 110 for an effective 21-1 compression ratio
IMHO calculating the effective compression ratio is completely worthless.
Basically, I base compression ratio and cam specs on desired power output and fuel octane. (other things like intercooling, vehicle weight, intended use (load), engine type, bore size, etc, etc, must also be taken into consideration when putting together a combination.)