I'm pretty sure it's only one at a time that is open but I want to make certain I'm right because I'm trying to do some math based upon this (I'm trying to calculate head-flow based upon total engine air-flow)

 

that can depend on the cam you are running, But I want to say 3 can be open somewhat at the same time..

 

OK here is what I have:
(note this is not in the correct firing order) IO = Intake Open EO = Exhaust Open IC = Intake Closed EC = Exhaust Closed
1 Bottom Intake Stroke, IO EC
2 1/2 Down Intake Stroke, IO EC
3 Top Intake Stroke IO EO (overlap)
4 1/2 Up Exhaust Stroke IC EO
5 Bottom Exhaust Stroke IC EO
6 1/2 Down Powerstroke IC EC
7 Top Powerstroke IC EC
8 1/2 Up Compresion IC EC

Ok, I think I am right on this

 

Isn't that what "overlap"

 

I mean: how many are completely open ??...I know about the others that are opening and closing (and calculating percentages for those valves)

 

WOW...that was WAY more dedicated than I got when trying to figue this out....Good Job and great info

 

Overlap is when the Intake and Exhaust Valves are open at the same time, and the turbulence accelerates the exhaust out, and atomizes the fuel better. IE: LSA Lobe Seperation Angle, the angle between the peak of the intake and exhaust valves, always less than the duration of a cam...the more overlap the higher the RPM range of the cam (amount of time both valves are open, there is a magic number)

 

C.... the answer is C....

 

.....

 

I am going to say 2 (fully open), the intake valve on one cylinder, and the exhaust valve on the opposite cylinder. Or if you have a Mazda Rx8 you will have 0 valves open, hell you have 0 valves, damn rotary engine.