I have a question. When you look up the specs of an engine and it says 8:1 for compression ratio what is that a ratio of? Cylinder volume at BDC compared to TDC?
You are compressing the atmospheric pressure (14.7 psi at sea level) 8 times on an 8:1 ratio. If there is absolutely no leakage of compression your gauge should read 117.6 psi at sea level.<br />Backlash
Thanks Backlash Ive been wondering about that for years.<br /><br />Wetwolf Im sure someone on this forum knows that. If you dont get an answer start a new topic.
If you really want to know you need the volume of the cylinder head space (Vh). You can measure it if you have a burrette like they use in a laboratory by filling it with water and measuring how much it takes.<br /><br />If the volume of the cylinder =Vc<br />the volume of the head =Vh<br />and the volume of the cylinder and head = Vc+Vh <br /><br />The compression ratio is the ratio (Vc+Vh)/Vh.<br /><br />Vc= stroke*Pi*(bore/2)squared<br /><br />So if your head Vh was 50cc and<br />your cylinder Vc was 500cc<br />Vc+Vh would be 550cc and your compression ratio would be 550/50 which is 11:1
<br /><br />Wolf