I get 10.65.

3.43 is what I came up with for your valve reliefs. I think you're getting different results based off what people are calculating for that.

110 CC is 6.71261 CI. The volume of your bore with the piston 1/2 inch down should be 6.50332 CI. The difference of 0.20929 converts back to 3.43 CC for the valve reliefs.

This is a flat top piston I assume?

Aren't you the madscientist? I thought you would have been good at math too

I think along with the rounding errors, depending on how far out you take it after the decimal, is how far out you take pi.

I used:
708.2 swept
12.2 gasket
67.0 head
3.35 piston
-9.4 deck height
-----------
781.35 total
73.15 total minus swept
-----------
10.68 (781.35/73.15)

Depending on the ring down placement and the actual piston diameter above the ring, there's going to be another 1-1.5cc there, so in reality it's more like 10.5-10.55:1.

I ASSumed the 3.32cc valve relief to be correct, however I even got a different result from yours when I calculate the volumes.
Pi*R squared*.500= 106.62cc
110cc-106.62cc=3.38cc making the Comp ratio 10.658:1

But yes, I would expect a scientist to be stellar at math as well

When I do the fill volume check on motors that have a dome above the deck hieght or positive deck hieght piston to figure out the dome volume I use a small needle nose end on my small hand held grease gun to seal the tops of the piston tops to the cylinder walls and I know thier is a small amount above the rings that I don't have filled so like already posted I could add another 1.0 to 2.0 CCfor that, I don't NHRA doesn't add any more to thier figures so I don't either

WRT "the actual piston diameter above the ring"

That's included in the fill volume, but not in the deck height, because it assumes the dome is actual bore size - which is never true.

How are you getting 73.15 for a chamber volume?

I get 67 for the chamber, 12.2 for the gasket and approximately 3.5 for the DISH that I am measuring. That would be:
67
12.2
3.5
for a total of 82.7

With a swept volume of 706.3 plus the chamber volume of 82.7 is 789 divided by 82.7 is 9.54


I can do math. Its just this one is pissing me way off.

Its simple math but we are all getting different numbers. Im losing the last bit of my mind thats left.

I always use the CR calculator on Diamond Piston's web site. Pretty much fool-proof... ==> diamondracing.net

Tim, the 10.65 is a good number. You are forgetting that the positive deck is reducing your chamber volume.

It doesn't say that's the chamber volume....... It's the total volume minus the swept volume.

Maybe he's at a higher altitude...

SPECIAL THANKS to Mike at B3 racing engines. I called him on the phone and he held my hand and walked me through my math mistake.

Porter has his numbers correct. Later tonight I will re-calculate the CR on this project out to the 3rd digit and then I'll be good to go.

It will be close to 10.5:1 or so.

Gotta remember to calculate the flat that comes out of the bore. That's where DP got the extra 9 cc's that I was missing.

Thanks to all that posted and especially Mike.

What do you do for a living?

Retired machinist, weldor and gunsmith. I still do some of all of it when I want to or need to.

Fix that carb yet............

10.6776658 LOL!

10.68

Sheeeeeeeeiiiiiiiiitt!!!

I'm slow as hell. It runs but don't drive yet. Front shocks will be here late this week. I'll get it lined up next week.

What a PITA.