OK. I've heard about 22cc domes, 19cc...etc
Does this represent the size of the dome itself (over the squish), or is it the volume when the piston is at its higher point?
Thanks

 

It's the flat plate volume of the dome. The FPV is the volume of the dome including the pocket, squish band area, and in some cases even the spark plug itself installed.

To determine the FPV, orient the dome level with the pocket up. Install your normal spark plug. With a clean piece of plexi-glass apply a very thin coat of grease to the gasket mating surface. Your plexi will have a 1/2" or so hole drilled somewhere near where you can position the hole to the edge of the outer diameter of the squish band. Now with your calibarted burrette full of a light oil, Marvel Mystery oil works great(or graduated cylinder, or even in more of a pinch a syringe of sufficient size) begin filling the dome up with the oil until the dome is full, rock the dome as needed to expell the air bubbles out the same hole we filled the dome up with. Record your number of CC's. This is the FPV, and most often the number that is advertised such as the 21, 20, 19 cc's domes available. Heat ranges of spark plugs will typically vary by .1 of a cc. As in a B8ES will have .1 less than a B9ES.

The FPV differs from the trapped volume. Trapped volume is the volume trapped above the piston at TDC. To determine the trapped volume you'll need the piston crown volume (PCV), the deck hgt volume (DHV), the head gasket volume(HGV) and the FPV

Trapped volume=DHV + HGV + FPV - PCV

 

i learned the hard way isn't it the lower the number on plugs the hotter?? b8es is hotter than a b9es by .1 ??? maybe i'm wrong i don't know but that is what i thought.

-Ben #51-

 

The difference in plug heat ranges has an influence on the FPV of a head/dome by .1 cc. Your are right that the lower the number of a NGK spark plug, the "hotter" the heat range. I think that you may be a tad confused about the .1 cc difference, it had to do with head assessment and not so much with how a plug will operate.