[3G_SDS]

Subject: How do you figure final compression ratio for supercharger applications?
Answer:
The formula is: FCR= (Boost/14.7)/1xCR FCR: Final Compression Ratio CR: Compression Ratio

Comp.Ratio Boost (in pounds per square inch)
SEE LINK FOR CHART:
http://www.rpmrons.com/detonation.html#supercharger

Final compression ratios above 12.4:1 are not recommended for use with "premium pump gasoline."
The higher the final compression ratio, the higher the octane rating of the gasoline must be, in order to avoid detonation and serious engine damage.

Altitude plays an important role in determining compression ratios. If the altitude in the area where the vehicle is driven is significantly higher than sea level, then the compression ratios will vary. To determine the effects of the altitude on a calculated compression ratio, us the following formula: Corrected Compression Ratio = FCR - (altitude / 1000) x 0.2

 

[callmeebryan]

:twothumb:

So basically, to rework the equation, If you know how much psi you are planning on running, in order to find out what compression pistons would be good for use with premium pump gas, the equation would be this.

(Piston Compression Ratio)= (12.4)/(Boost/14.7)

So if i wanted to run 20 psi on premium pump gas, this is what it would look like.

(Piston Compression Ratio)= (12.4)/(20/14.7)
Piston compression ratio= 9.1:1

 

[NAPALM]

THese things arent very practical in the real world.
It all comes down to tuning...

 

[Guest]

THese things arent very practical in the real world.
It all comes down to tuning...

Does the formula tell you you'll need 5:1 pistons? :squint:

 

[MattS00]

THese things arent very practical in the real world.
It all comes down to tuning...

True. i.e. what octane is premium. It also doesn't mention anything about changes to timing advance, combution chamber design, spark plug heat range, combustion chamber burn rate, cam overlap (which can lower compression), A/F ratio, or even how long the boost is applied to the motor (1/4 mile or road track). :noway:

 

[3G_SDS]

I just thought it was fun brain food. If it were the bible my engine would be toast.