Fbronco -

The volume "swept" by the piston is one part of the initial volume. The rest of the initial volume is the "static" or "unswept volume consisting of the space that remains when the piston is at Top Dead Center. Imagine the piston TDC. The amount of liquid that would occupy the remaing area is the static volume.

Since the ratio of compression is determined by:

(Initial Volume) divided by (Final Volume)

then it becomes easy to see that these are represented by:

(swept + static) divided by (static).

Omitting the static volume from the total Initial Volume will not give a correct representation of the CR.

I have no idea whether I am helping you visualize this. Hope I'm helping.

M

mcollinstn, that helps. My problem is that I don't see how replacing the stroke with the deck height in the formula for the swept volume will get you the space between the piston at TDC and the top of the deck. I do understand that you need this along with the gasket volume and combustion chamber in head to get the true compression ratio. Maybe I'm not sure what the "stroke" actually means. If that is the length the top of the pistion moves from bottom to top, then you would still need to figure out how far the piston is away from the deck height when it is at TDC? Right? And use that measurement to replace the stroke in the formula you used for "swept" volume?

Thanks

Ahh, Bronco, thats not how it works, so it shouldnt make sense :)

The deck / piston clearance could be calculated with the following info:

Deck Height

Crank Throw (half of the stroke)

Rod length

Distance from the center of the piston pin to the top of the piston (Piston 'height')

It would be

Deck - (Throw + Rod + Piston)

I've got too much time on my hands so I drew this out to hopefully help everyone visualize this discussion...


--Adam

Jeez, you guys draw some really neat pictures.:D Now, as Yosemite Sam would say, "Alright rabbit, draw a gun!"

This is what happends when you are an unemployed sales engineer with a background in network architecture, hehe..

You get programmed to turn dry stuff into a pretty picture... Then get deprived of the need. hehe

:)

--Adam