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Compression ratio formula, need a little help or info

kart43, with everything else being equal, in my information provided. What would the compression ratio be with a 32cc head with your calculations? Also I was just rounding off the compression ratio you guys gave me. I guess I am used to rounding off compression ratios. Like if it was 11.1-1 I'd just say I have 11-1, I have 11.3-1 I just round it up to 11.5-1
 
Kart43 said:
The head gasket volume does not get included in the pistons swept volume when you have zero pop up The head gasket volume now becomes part of the combustion chamber.
Click to expand...
Having read this several times i think the light came on today .
Effectively lowering the compression ratio .
Now the question . With pop -up it becomes part of the pistons swept volume?
 
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Can't the head volume just be cc'd with the engine assembled (at TDC with the valves closed)? That eliminates all the issues, correct?
 
flattop1 said:
Having read this several times i think the light came on today .
Effectively lowering the compression ratio .
Now the question . With pop -up it becomes part of the pistons swept volume? In turn it would raise the compression ratio?
(Because the piston take up some of the volume of the gasket)
Click to expand...
Pop-up does not affect the swept volume, it only changes the volume in the head at top dead center. Same with the dished piston. A dish in the piston adds to the combustion chamber volume.
 
Can we think of swept volume as that volume defined by bore and stroke?

The shape and volume of the dome or dish is the same at the top of the stroke as it is at the bottom.
 
Swept volume is the displacement of the piston, the dome or dish plays no part until it enters the combustion chamber. Yes the most accurate way to calculate would be determine the CC volume when engine is assembled, that accounts for space around piston down to top ring, any difference in depth of valves, and accurate gasket volume. Flattop1 if the piston rises above or below the deck, all of the volume above the piston has to be accounted for in the combustion chamber. CCing assembled engine is best way.
 
Looks like I need to do it that way, assembled As that’s probably 100% accurate.
I guess with the head off gives you more a good estimate, head on is 100% accurate?
is there a different formula Or calculation to use with the head assembled?
or do u use the same calculations In this thread?
 
Put piston at tdc
Set up burrette with more volume than possible for displacement and combustion chamber.
fill combustion chamber thru spark plug hole. This is cc of your combustion chamber.
Roll engine to bdc.
Finish fill to top of spark plug hole. This is your total volume.

total volume /cc of combustion chamber = compression ratio.

The spark plug will affect the cc of combustion chamber slightly.
That difference could be measured with the head off and the burrette.
 
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