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[Touring83]

I am looking at some pistons/cylinders that advertise 10.5 to 1 compression with 85cc chambers. If I have 96cc chambers, would this cause compression to be higher or lower with this advertised kit?

Thanks!

[coloradotom]

Lower

[Touring83]

Thanks for the reply. That's too bad, I was looking to head the other way, not lower.

[Yellow09SERG]

http://bigboyzcycles.com/TwinCamComp.htm

Try this link. Enter your information and it should give you an idea and get you close

[HD Street Performance]

Consider the dome shape
 The cvo, water cooled bathtub, and regular bathtub all take a different shape.
What is the displacement,  head being used and the camshaft?

[grc]

Static compression ratio is the mathematical ratio between the entire volume of the cylinder and combustion chamber when the piston is at bottom dead center and the volume when the piston is at top dead center.  The combustion chamber volume is part of both numbers.

Here's a simplified example:

Swept volume of cylinder = 50 cubic inches.
Volume of combustion chamber = 5.19 cubic inches (85cc).
Total volume of cylinder at BDC = 55.19 cubic inches.
Compression ratio = 55.19/5.19 = 10.6:1

Swept Volume = 50 cubic inches
Volume of combustion chamber = 5.86 cubic inches (96cc)
Total volume of cylinder at BDC = 55.86 cubic inches
Compression ratio = 55.86/5.86 = 9.53:1


Before anyone jumps in to tell me I'm not figuring in deck height, piston dome volume, gasket thickness etc., etc., this was not intended to be a full tutorial on compression ratios.  All those numbers are assumed to be the same for both examples.

Jerry