I now have the gasket info to enter for a corrected CR ( compression Ratio). Recap: .25 over bore for new cylinder volume,head cc of 49, gasket #s for cc. I had a thought of coming up with a easy way to do the math for correction and computation of the numbers. SO I built a spreed sheet to enter the information and made a work book for alteration based on the base line information. The method only required the numbers already taken and the additon of piston crown cc and exhaust port height to top of cylinder. This based on using stock base gasket.

SO I need to find out for this method the cc difference between the piton dome cc and the cylinder volume for the piston crown height. In order to do this I will take a .25 over cylinder and old piston and get to work.

First: I installed a copper wire arond the piston in the ring groove to help seal and hold pistonin place for cc the cylinder.

Second: I installed the piston in the jug ( cylinder) and set the piston crown at the top of the cylinder ( deck). using a flat bar and bolting it down to the jug using the head studs and some nuts.

Third: I installed a grease seal around the piston land area ( edge of piston crown to top ring) for sealing. Usally the land area is fiquerd into the equation , however for this it is not that critucial.

Fourth: I measured the distance from piston crown edge to deck ( top of cylinder). I willuse this number to calculate the total vloume like I would do for the head gasket and get total CC's.

Fifth: I will get out the fluid and cc using the same method as I did for the head. I then will take this number and subtract it from the volume number to get a correction factor for the piston dome.

Sixth: Enter this into the spreedsheet for the calculation.

The easy method I will call it now can be done by simply mesuring the corrected swept volume of the cylinder by using the bore # and the top of ehaust to top of deck( top of cylinder). This will give me a correct swept volume in cc's and I can add the gasket, the head, total and then subtract the piston dome and use a formula to find corrected CR.

With this base information in a work book one can change the values and dial in the modafaction and tract changes in CR based on bores, head and deck numbers. If for some reson you change type of base or use spacer plate a simple change can be made to the calculate the CR effects.

I find this may be usefull for pre port and modafaction change before you blow one up. What if you run the limits of pump gas like I do It will help make slight changed to keep in check. Plus by entering the number ahead of the time you have a working guide to go by. This is just one step in the rebuild process not the only one when you go changing things. I now have a way to do pre work instead of post work modafactions, I hope.