Comp ratio calculations

[jimmy six]

Bring up this website and go to calculations for static and "actual" CR. Have your head, piston and cam card ready....www.KB-Silvolite.com          Good Luck...JD was an eye opener for me

[willieworld]

http://www.rbracing-rsr.com/compstaticcalc.html                  also there is a bunch of other cool stuff   willie

buchta



click on calculations at bottom of page

[Milwaukee Midget]

Thank you for this, Jimmy.  This is a great starting point for some numbers that aren't always easy for a knucklehead like me to figure.

Bookmarked.

[fredvance]

Anybody know what the cc's of an '08 Busa piston is??

[jimmy six]

The biggest problem is knowing what the cc's of your popup piston is. If they are off the shelf call the manufacturer they should give you this info. You can do it your self with releasing agent and plaster of paris.

Even the diameter of a head gasket changes things. Since I have a .000" deck height and use an .060" thick gasket now I can "trim" some off the block to raise the compression. I was surprised to see what .020" did. I have the luxury of a fairly low RPM engine and steel rods which helps if I make the decision to do it. Still need to watch the gap of the valves near overlap...Good Luck to all.

PS: when you factor in the cam timing you get to see the real picture

[VeeTwin]

An easy way to do dome volume is the 1" down test. Grease the top ring and put the piston 1" down the bore and fill the area above it with a burette. The volume of the cylinder at 1" (i.e. pi *r squared * 1) minus the measurement gives you the dome volume.

You don't have to do it at one inch of course, if you have one of those foreign jobbers.

[Dean Los Angeles]

fill the area above it with a burette.

Do I crush the glass first? 

[Peter Jack]

fill the area above it with a burette.

Do I crush the glass first? 

Don't you hate the racing off season.

Pete

[panic]

The original reason for the "1 inch fill" rule was practical rather than scientific.
1" was the tallest compression dome on the 426 hemi engine, and the entire dome must be submerged for fill volume to work.
If you're not sure and have a strange (alcohol) engine, use whatever depth you need to get the pop below the deck, and substitute that distance in the volume math as the height of the cylinder.