| Author | Message | ||
     Roc |
Engine compression ratio is 10/1, what should compression test be in PSI? | ||
| Blake |
Minimum 120 PSI with no more than 10 PSI difference between the two cylinders. In theoretical terms, ten times ambient (atmospheric) pressure would be right around 147 PSIA (absolute pressure) or more appropriately for this particular discussion, 132.3 PSIG (gauge pressure). Gauge pressure equals absolute pressure minus ambient atmospheric pressure (PSIG = PSIA - PATM). Actual compression produced in a cranking engine is dependent also on dynamic factors. For instance, big cams with a lot of intake/exhaust overlap can show low compression during cranking via starter. But get the engine revved up into the powerband and exhaust scavenging and tuned intake ram effect can produce volumetric efficiencies exceeding 1.0, which means that with the help of the aforementioned factors, ambient air is being compressed as it enters the combustion chamber to greater than ambient pressure. A hot engine can also inflate engine compression test results since as the ambient air is heated inside a hot combustion chamber, its pressure rises; if liquid fuel is vaporizing inside the combustion chamber that will add to the measured compression too, just like how the CO2 in beer or soda adds to the pressure in a bottle when it changes from liquid to gasseous state. | ||
| 99buellx1 |
I think there was an answer somewhere in there, lets see if we can find it.
Ahhh, there it is.  Don't you have some pampering to take care of? (good on ya btw, give her my best) | ||
| Mbsween |
Don't forget to open the throttle wide when doing the test, lets max air in | ||
| Blake |
Craig, Gourmet meal has been prepared, served and voraciously consumed. Hydrocodone has been administered. The pampered one sleeps.  | ||
| 99buellx1 |
"Well wake her ass up, we've got to win tomorrow!"  Now, back to the eBay thread. Or is it the shonk thread? |
