Hi guys,
Got a ? for anyone of you who don't mind bringing up these conversion site or may have the immediate knowledge to figure this one out. I have a mitsubishi 4G63 (JDM) engine in my Hyundai Elantra and after running a compression test on it, the average compression was 225psi. What compression ratio does that equate to? I'm assuming in the ballpark of 10.4:1 . I know it has more compression than the U.S. engines because this thing pings with the correct timing and it even pulls harder. Any help with this would be greatl appreciated.
PSI to Compression conversion
Well on one site I found the formula:
Compression = (CR - 1)^1.1 * Atmospheric Pressure
But they also said that you can use an exponent factor of 1.2
Making:
Compression = (CR - 1)^1.2 * Atmospheric Pressure
So, taking your case of 225 psi into account I calculated the following:
Using an exponent factor of 1.1 and assuming 14.7 psi of atmospheric pressure:
225 = (CR - 1)^1.1 * 14.7
(CR - 1)^1.1 = 15.30612245
Log<CR - 1> 15.30612245 = 1.1 <-- The <> brackets mean "to the base of .."
Log 15.30612245 / Log (CR - 1) = 1.1
Log (CR - 1) = Log 15.30612245 / 1.1
CR = log^ -1 {Log 15.30612245 / 1.1} + 1
CR = 12.94401023
Now looking at that, I find a stock CR of 12.9:1 to be way off. So now I'll use the 1.2 exponent factor:
CR = log^ -1 {Log 15.30612245 / 1.2} + 1
CR = 10.71376635
Now, we've got a CR of 10.7:1... which sounds more realistic.
Hope this helps,
Pete
Compression = (CR - 1)^1.1 * Atmospheric Pressure
But they also said that you can use an exponent factor of 1.2
Making:
Compression = (CR - 1)^1.2 * Atmospheric Pressure
So, taking your case of 225 psi into account I calculated the following:
Using an exponent factor of 1.1 and assuming 14.7 psi of atmospheric pressure:
225 = (CR - 1)^1.1 * 14.7
(CR - 1)^1.1 = 15.30612245
Log<CR - 1> 15.30612245 = 1.1 <-- The <> brackets mean "to the base of .."
Log 15.30612245 / Log (CR - 1) = 1.1
Log (CR - 1) = Log 15.30612245 / 1.1
CR = log^ -1 {Log 15.30612245 / 1.1} + 1
CR = 12.94401023
Now looking at that, I find a stock CR of 12.9:1 to be way off. So now I'll use the 1.2 exponent factor:
CR = log^ -1 {Log 15.30612245 / 1.2} + 1
CR = 10.71376635
Now, we've got a CR of 10.7:1... which sounds more realistic.
Hope this helps,
Pete
sounds good enough to me! This engine has a crap load of compression which means my Elantra can now beat up on SE-R's Civic Si's and most other N/A 4 cylinders:D LMAO.