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Old 12-14-2012, 01:56 PM
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Let's call the cylinder volume 727.4 cc's.
Piston crown 11.0 cc's
Chambers 59.0 cc's
Piston deck height 7.3 cc's @0.035".
Gasket (0.015"/0.016") 3.3 cc's
Total 808.0 cc's
Total less cylinder 80.6 cc's
Divide the larger by the smaller and find 10.02:1 static compression ratio with ~0.050" squish.
If I could check both decks and both heads with a precision machinist's straightedge and found that all surfaces were flat within 0.002" and I was on a tight budget, that's how I'd build the motor. I might use a cam something like this one that closes the intake valve at 42 degrees ABDC.
Crane Hydraulic Flat Tappet Camshafts 114561 -
This cam would generate a dynamic compression ratio of 8.46:1, which I feel would work with pump gas and a 0.050" squish. You'll need to use more ignition timing at the crank and curve the weights in the dizzy for max 34 degrees, all in by 2800. I think I'd use a 3500 stall converter.

If any decks were wavy beyond 0.002", I would not use a steel shim gasket without cutting the decks/heads for flat.

DanielC, you are correct, with a dish shaped like this, math won't get you there, you should pour the crown with alcohol. You do not, however, have to position the piston down in the bore by 1". This will keep you filling the burette too many times and allow an error. You only need the piston down in the bore far enough for fluid to flow across the crown, like say 0.030". Then you do the math as if the dish were not there to find the volume of that space: (.7854) x 4.03 x 4.03 x .03 x 16.387, which would calculate to 6.27 cc's. You would write that down and then pour the volume. If, for instance, the fluid required to fill the dish and crown was 17.5 cc's, then you would subtract 6.27 from 17.5 and find a dish volume of 11.23 cc's.

Last edited by techinspector1; 12-14-2012 at 02:08 PM.
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