Determining Compression?

[mustang652]

Tried using the search mode, but no specificanswer. Having to drop back a few and punt as I and the car have been down since mid October. What are the steps I need to do to determine what's the compression ratio.

 

[fxp]

Try Bowling and Grippo

http://www.bgsoflex.com/auto.html

has a compression calculator 4 down on the left.

 

[jahearne]

http://falconperformance.sundog.net/compcalculator.asp

or you can take apart the motor to cc the head, piston dish/deck hieght and head gasket like I did. I wished I was smart enough to think of cc'ing the entire motor while it was assembled on the engine stand. You know, rotate the motor until the spark plug hole was level, the piston at TDC with both valves closed. Just measure what it takes to fill the combustion chamber right up the to bottom of the spark plug hole threads to get the entire combustion chamber volume:

CR = ( entire combustion chamber + piston cylinder volume ) / ( entire combustion chamber )

Piston cylinder volume = ( engine size ) / 6 = ( pi/4 ) x (bore)^2 x (stroke)

Head combustion chamber + dished piston + deck heigth + head gasket = entire combustion chamber volume

To convert inches into centimeters multiply by 2.54

A compressed composite head gasket takes up about 9 - 10 cc's.

Somebody double check me. I wrote this down from memory. I just did my motor last week.

 

[mustang652]

Thanks for the info. Due to some gasket problems, the heads got to come back off, so I'll cc the head and the top of the piston at that time. What is ment by deck height?

 

[jahearne]

Deck height is the distance between the top of the piston and the top of the block, the deck. On my 250, it is quite a lot.

cc'ing the piston at TDC gives you the volume of the piston dish and cylinder volume of the deck height all together.