Originally Posted by Phantom
I figured that if he wanted to increase the compression from 9.4:1 to 9.99:1 the total hight of the cylinder would be decreased .03" changing the total volume from 231.4ci to 229.3ci thats a 2.1ci decrease in volume
Basically what Ben said in the post following yours. An example. Ford produced the 4.6L v8(281 CI) from 91 till current. Between 91 to 98, the head design was just about identical(minor changes in port sizes and valve guide placement). The one constant was the combustion chamber in those heads(except the 96-98 heads had a little more swirl fin). Referred to by us Ford guys as NPI Heads. 96-98 heads(F5 castings) were superior to the 91 heads(F1 castings), and 92-95 heads(F2 and F4 castings). All of those year heads had a 53CC combustion chamber(I think, I can't remember specifically). All of these had a 9.0:1 CR from the factory
The 99+ heads(PI heads) were different. Bigger valves, ports, cams and combustion chamber. Faster burning, much like the 3800(heart shaped). Those heads had a 43CC combustion chamber. The only difference throughout the entire shortblock(besides plant manufacturing), was the pistons going from 10.5CC(91 to 9
to 16.5cc (99 to current). The 99+ 4.6L had a factory CR of 9.4:1. The engine still measured out to 281 CI or 4.6L
This only accounts for the SOHC 16 valve 4.6L'*, not the SOHC 24 valve and DOHC 32 valve engines.
Again, simply put. The displacement of the engine is measured by the bore and stroke of the short block and does not change unless the stroke/bore is altered. Decking the block down is another idea to raise CR, but not needed as the heads can be milled as far as anyone would ever need them. Even decking the block doesn't change the displacement until you get the top of the piston coming past the deck.
Now if i could only do a .040" overbore on MY engine... I'm limited to .020" max because the headgasket fire ring is so small:(