Oh, wait, I added the gasket to the cylinder instead of the chamber. Be right back.

 

Sorry. It is 9.79:1 with the numbers you gave, using pi times radius squared, times stroke for the cylinder, and having google convert to cc gives 665.706449. The same formula gives 9.98299939 for the gasket. Gasket plus chamber equals 67.98. 665.706449 divided by 67.98 equals 9.79.

 

http://www.diamondracing.net/cocalc.htm

 

I could probably come up with more answers if I keep trying.

 

I would like to apologize for being so wrong and give an explanation. I was figuring the ratio of piston displacement to combustion chamber. I should have been figuring the ratio of overall volume (CI + cc) to chamber volume (cc). Maybe my epiphany will help others.

 

I still don't know all the parameters of this calculator to fill this out. Anybody?

 

8 to 9 lbs

 

The 10.79 that the calculator gives using the numbers you supplied will be all you need to know to answer your original question. At 10:1 compression (not figured by me), my truck is a little detonation prone at 9 psi. It shows up immediately after a fill up if they lied about what they sold me. Your engine should be less sensitive because of the smaller bore size. My guess is that with the added compression it will be similar to mine in octane sensitivity, and I'm happy with mine as a daily driver. As long as your low octane spark table is safe, I think you will be OK.