peak cylinder pressure. u talking about an engine with the spark grounded out so it's not firing? if ur talking about a running engine, it would obviously have to be a few degrees after tdc, making the power to push the piston down. where would depend on spark timing, octane, compression ratio, etc. but if ur talking about just cranking a motor and where the highest compression is reached, i would say it would also depend on where in the chamber you are talking. top of piston would be top dead center, b/c it's being compressed into the smallest area and the piston is doin the work, but if ur talking about the top of the combustion chamber where the spark plug is, i would say a few degrees after tdc b/c of squish velocity and the momentum of the air. it would take a (although very small) fraction of a second for that pressure wave being created by the piston to compress thru the air and reach the spark plug. hope that made sense lol.
the 195 duration would have a (very slightly) smaller static compression ratio compared with the 190 b/c the top of the exhaust port is higher. so although you are compressing into the same area, your starting from a slightly smaller volume. but thats just static, dealing with simple math. when you factor in for what kind of pipe ur running a dynamic compression ratio might actually be higher cuase it give the pipe that little bit longer time to push the air back into the chamber.
i agree with samolia about the compression ratios and octane. ideal gas law states that if you compress a gas it gets hotter. one proffessor showed us this crazy little experiment that made me realize just how hot that compressed gas gets. he took a glass tube sealed at one end and put a very small piece of toilet paper in it. then took a rod that fit tightly into the tube and set the bottom of the tube on the table and smacked the rod, creating like a small combustion chamber, but without spark. when he hit it the toilet paper burst into flames. all b/c of the air getting heated up, hot enough to light the paper. that's exactly what happens when you get detonation, only the toilet paper is replaced with gasoline.
this part is irrelevant so don't read it unless ur bored. he told us a story that he read on one of his physics professors forum things that it was suggested to use a few square centimeters of flash paper. so he did it in class once and it blew the glass tube apart, mildly injuring a few of the the students. lol. he went back on and told his forum what happened and the guy that suggested it said ooops, i meant a few square millimeters, not centimeters. lol. so he put 100 times as much as he should have. then he told us this is why he always harps on us about including appropriate units with our answers.
ok flotek, so your talking dynamic compression. makes sense. but also then with dynamic compression what kinda pipe u run is going to effect compression too....
gotta remember. the engine is a system, not just a compilation of parts.