Crankcase Compression Ratio

[djackbanshee]

Hey

Anyone here would know how to calculate the CRANKCASE compression ratio ?

Thanks

[RadarRacing]

Are you actually wanting the crankcase volume?Crankcase compression??? or are you wanting to get the uncorrected compression ratio of the combustion chambers?

[djackbanshee]

yes crankcase compression volume

 

i want to know the exact procedure to calculate it , i know the piston has to be at tdc and then the motor filled with liquid , but up to where i must fill with liquid , reed valves ? carb boot ? carb ?

[RadarRacing]

Maybe I'm wrong but I believe you are wanting to figure your cranking compression to figure octane requirements, dome size requirements etc.

You dont fill the bottom of the motor you fill the top above the piston. Slightly oil or grease the cylinders so the rings seal good and go to TDC and fill up the combustion chamber with oil till it fills right up to where the bottom of the sparkplug would be. Your motor has to be inclined so you dont have an airpocket in the head/combustion chamber.

Measure the CCs of oil that filled it up then take the displacement of only the cylinder you are measuring so half the CCs of a banshee's 2 cylinders. Take the Displacement in CCs divided by the volume of oil it held.

Example if it held 18 ccs of oil in one of the the combustion chambers and you have a 348ccs twin cylinder divided by 2 to only measure one cylinder =

174cc in one cylinder divided by the 18 ccs = 9.66.. to one compression.

CCs of cyl / trapped volume = comp ratio - 1

[djackbanshee]

Thanks But no i am really looking for crankcase compression also know as primary compression