Quote:
Originally Posted by snbush67
Because the 911 pistons are shaped hemispherical and protrude into the combustion chamber the edge or shoulder of the 911 piston is used to determine deck height.
They way that I understand it is that deck height is the difference between the shoulder of the piston when it is at TDC, and the top of the cylinder. The shoulder of the piston is the "deck". Whereas if you had a normal flat piston you would use the top as the "deck". To determine deck height is to determine the distance between the deck and the top of the cylinder. I may be stating this wrong as some people refer to the top of the cylinder as the deck, either way deck height is the difference between the two.
The squish area may be different depending on the shape of the head and the piston. For example the shape of the head where it meets the cylinder is initially the same shape as the cylinder wall so it is a continuance of the cylinder, and in some heads the pistons deck can continue past the seam into the head.
I hope you can see the difference, the thing is I do not think this is the way it is explained in Wayne's book. And after saying all of this I really don't think deck height by itself matters, only the squish actually matters.
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Wayne's book, as great as it is, does not do a great job of explaining this.
Your explanation is correct: deck height is the distance between the "deck" of the cylinder (the term originated long ago-- think about the cylinder head mating surface of a Model T iron block to visualize "deck") and the theoretical top of the piston WITHOUT THE DOME. Some JE pistons have a flat land machined into the edge of the piston to make it convenient to measure. Others, you have to measure then subtract the dome height. But it takes you to the same place.
Many confuse head-to-piston clearance with deck height which is only an accurate use of the term with a flat top piston. Think back to the Model T example. Or 930 turbo pistons. . .
