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Discussion Starter #1
I'm looking for a little bit of cheap power out my cb350 twin by milling the head down, but I can't find a calculator online to figure out how much to take off to get different compression ratios. It's the stock bore & stroke with about 31cc of volume in the head and the stock domed pistons(no idea on what the cc of the dome is). I know it's a popular bike for this kind of stuff, so if any of you experts could hook me up with something to figure this out with or even tell me how much you've taken off and what your ratio was I would be extremely grateful.

p.s.- If anyone could share the stock squish clearance that would be awesome too, my motor is in pieces so I can't measure it :/
 

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You can wrap something around the piston that is fluid tight, pour in fluid from an accurately marked lap type beaker thingie. Since you know the bore of the piston x the height you fill with liquid that gives you how much liquid SHOULD be in there without the dome....pour the liquid back into the beaker...measure how much actually WAS in there...the difference gives you the volume of the dome.

Chamber volume, plus the bore x gasket thicknes = chamber volume. Then minus the dome volume, gives you the chamber volume at TDC. With that, plus the bore and stroke you should be able to calculate compression.
The do the same thing over again subtracting (bore x mill amount) from the chamber volume, should show you an estimate of the compression change.
JohnnyB
 

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Discussion Starter #4
I found the dome volume by pressing it into play dough to make a mold then filling that with water from a syringe. I don't know the compressed gasket thickness is, but I'm going to look around the net a little and see if I can't figure it out. Thanks for the input jbranson.
 
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