12-1 If I shave the head?

Total Combustion Chamber Volume For a Specific Compression Ratio

Cylinder head chamber volume = swept volume / (desired compression ratio - 1)

Example: Swept volume = 716.62 cc
Desired compression ratio = 11:1

Cylinder head chamber volume = swept volume / (desired compression ratio - 1)
Cylinder head chamber volume = 716.62 / (11:1 - 1)
Cylinder head chamber volume = 71.66 cc

Compression Ratio

Compression ratio = (swept volume + total chamber volume) / total chamber volume

It is important that we understand two terms and their relationship to compression ratio: Swept Volume and Total Chamber Volume. Swept Volume is the area the piston travels through bottom dead center to top dead center. Total Chamber Volume is all the area above the piston at top dead center. This would include the area above the piston in the cylinder block, the area of the compressed head gasket, the combustion chamber, the valve pocket, and the dome of the piston. The compression ratio is the relationship of the swept volume to the total chamber volume.

To start, we need to know the Swept Volume of one cylinder. The size of one cylinder figured in cubic centimeters.

Swept volume (cc) = cylinder bore diameter (inches) X cylinder bore diameter (inches) X stroke (inches) X 12.8704

Example: Cylinder head cc = 72.18 cc
Piston = flat top with two valve pockets that measure a total of 4 cc
Head gasket = 4.000" round and 0.038" thick when compressed
Deck clearance = The piston at top dead center is 0.010" below the surface of the deck

Gasket cc = bore X bore X compressed thickness X 12.8704
Gasket cc = 4.000 X 4.000 X 0.038 X 12.8704
Gasket cc = 7.83 cc

Deck clearance volume = bore X bore X deck clearance X 12.8704
Deck clearance volume = 4.000 X 4.000 X 0.010 12.8704
Deck clearance volume = 2.059 cc

Total chamber volume = 72.18 + 7.83 + 4 + 2.059
Total chamber volume = 86.07 cc

Now we are finally ready to calculate the compression ratio!

Example: Swept volume = 716.62 cc
Total chamber volume = 86.07 cc

Compression ratio = (swept volume + total chamber volume) / total chamber volume
Compression ratio = (716.16 + 86.07) / 86.07
Compression ratio = 9.33:1

Ok I went out and rode it. I found out what was choking it off at high rpm. I backed the timing down and it rev's to 10 and really scoots that last part! She's got enough to stand it sraight up and over at 9+ . That's cool with me. It's clean and mean right through to 10. Really gota hang on to that sucker. Keeps popping out of second and revving over. It's got is the best throttle responce roll on too. Wind it up and look out! This is exactly what I wanted. Now maybe some more cylinder pressure and better head flow. It super charges itself coming up, it's awesome, kind of scares me some too. It's a heavy bike. It doesn't mess around getting up there. Im holding the shifter up with my foot, so it doesn't pop out of second. Then I need to hit third but can't get to it fast enough (gota let the lever return to center then move it up for third. The bike is always needing another gear so quick. guess I'll be fixing that second gear for good this winter and putting on the better head. When I got this engine to haul at those high rpms , run smooth at idle, have excellent midrange, flat out move, It made my day. I got alot more out of it than I thought I would, now I need some bigger carbs. Can't wait to see what Larry will say about that head. That head and a mill might be right what the doctor orded for this combo.