Measuring Comp. Ratio?

[PINK71T/A]

This may sound stupid guys but how do you determine Compression ratio? Is it as easy as putting a compression tester on your engine if so how would you tell if you motor is apart? is there a formula? I had a guy asking me the other day and i was like Ummmm, looking like a idiot! i said i dunno! i remebering seeing a Magazine article once and they had a glass plate attached to the bottom of the cylinder head and they pumped fluid? into the Chamber and measured the fluid used and i guess what i got from the article was they were able to tell from that and some other measurements what the compression ratio was. I would be very grateful if someone could explain this to me better so i can have a better response next time instead of looking like Joe Dirt! id rather know instead of " How does a Posi-traction rearend on a Plymouth work! It just does!" Thanks for any answers to my Dumb question!

[jimbo7074]

There are many formulas out there,but you still have to measure certain things.You have to cc the heads to get that number,then you have to take into account the bore and stroke of the motor,head gasket thickness,and how far below the deck,or above the deck the piston is at TDC,and also if the piston has valve reliefs or a dished surface,and figure out how many cc's that tkes as well.If you have this information on hand the KB pistons website has a calculator,that you simply put in your figures and it will give you the number.

[sanborn]

Let me say it a little different from Jimbo. Compression Ratio is the relationship of swept volume to compressed volume.

Swept volume is the total volume required to fill the cylinder bore, cylinder head, valve reliefs, negative deck height, head gasket thickness at Bottom Dead Center.

Compressed volume is the total volume required to fill the cylinder,head,etc. at Top Dead Center.

Dividing the Compressed Volume into the Swept Volume yields Compression ratio.

[PINK71T/A]

Thanks Sanborn that makes sense! Thanks for the replies!