Time to go to work
oh good an expert, take it away lance i always like to learn...
First you need CCV which is combustion chamber volume
You'll need a 50cc glass burrette preferably with stand
Dial indicator
good set of accurate calipers
piece of clear plastic 1/4" X your dome od + 1/2". Drill 1/4" to 3/8" hole in the middle and debur.
Take head off,
roll engine to TDC,
lightly seal around edge of piston with grease. Try to gently push down @ edges to get good seal. Clean up any excess grease. Check your TDC again,
Re-install head
pour gas & oil mix that you run and fill to top of spark plug hole.
Record cc volume.
Pull head,
Screw spark plug in hole,
Put plug in vice and set a level across both ways, then lightly apply a very thin bead of Vaseline around on dome to seal against plastic. Press down firmly and or add weight to hold down.
pour through hole until full. You'll have to play with a little to get it level, just watch the bubble when it comes up against the plastic. When it comes up against bottom of hole in middle STOP!
Record cc volume. This is your head "flat plate volume". This is to reference to this dome only . Deduct plug hole volume from CCV, which is usually around 1.8 to 2cc. (You can measure this with your burrette) to be certain.
Now it's just math, divide cylinder volume, (stroke times bore) by CCV and you have your compression ratio pretty precise if you measured good.
You will do a squish to piston clearance with solder when you have head off also.
Now, the biggest things that is going to dictate what you can run for compression are head combustion chamber design which includes a whole lot of variables, of course fuel, altitude and all the rest pipes, pipes etc.>>>>>>>>!!! Your combustion chamber is going to dictate where your timing will be. We can get into that later.
Biggest thing I've noticed with people buying mod motors that don't have any idea what they bought, who can't find good info on the particular build, they end up with a disaster.
This will get just get you started. If this is too much bother for you to get a nice mod motor to run perfect, don't bother any more because it's just the beginning. I can steer you the right direction when I have time.
Good luck!