exhaust valves open?

[56 nomad]

hello,
I know many of you know this info by heart...i do not so i am hoping i can get pointed in the right direction.
will someone tell me where i can find information about the 911 valve train....more specifically i would like to know which exhaust valves are partially open as the engine rotates in the cylinders. i want to better understand the compression of the intake and exhaust cycle.
looking for some light reading.
regards, ben

[Tim L]

HowStuffWorks "Internal Combustion"

[56 nomad]

Originally Posted by Tim L

HowStuffWorks "Internal Combustion"

Tim,
thanks for responding ...let me ask the question another way ( same way?) as i understand how the internal combustion engine works but am trying to get a handle on the sequence of the cycle (combustion and ehaust). for example at tdc number 1 cylinder both valves are closed before combustion...in cylinder 6 (after 1 fires) exhaust closed intake beginning to open (drawing in fuel and air for combustion stroke etc. etc.
in the other cylinders which exhaust valves are beginning to open or are closed etc.
hope i made it clearer and not more confusing, ben

[Tim L]

it's the same in all cylinders it just happens in the sequence of the firing order of the engine in question. in a 6 cylinder there are two cylinders at top dead center at a time one is in compression and one is in exhaust then at 120 degrees of crank rotation the next two are up.... the firing sequence will tell you the order

[Flieger]

Do you want the valve timing for an individual cylinder- like the overlap? That info is in Porsche 911 Story by Paul Fere. The firing order is 1-6-2-4-3-5 I think.

[T77911S]

the only way i can think to answer it is starting with #1TDC, starting its power/down stroke after combustion.
you would also have to know what the cam timing of the motor you are talking about, IE when the valves open and close, if you wanted to be exact as far has how open/closed is a valve.

since one cylinder fires every 120 degrees of crank rotation,
#1 is TDC, the spark plug has fired, combustion has/is taken place and the piston is starting its power stroke, both valves closed.
#6 would be at 240 degrees, both valves are closed and it is on its compression stroke.
#2 would be at 120 degrees, and on the intake stroke with the intake valve open.
#4 would be at TDC, valve overlap (which is where cam timing is set), and it has just completed its exhaust stroke and begining its intake stroke. with most cams, both valve are slightly open with the exhaust closing and the intake opening.
#3 is at 240 degrees and on the exhaust stroke. exhaust open.
#5 is at 120 degrees nearing the bottom of its power stroke, both valves closed.

hope this helps.
start at TDC and work CCW in firing order.

[56 nomad]

Originally Posted by T77911S

the only way i can think to answer it is starting with #1TDC, starting its power/down stroke after combustion.
you would also have to know what the cam timing of the motor you are talking about, IE when the valves open and close, if you wanted to be exact as far has how open/closed is a valve.

since one cylinder fires every 120 degrees of crank rotation,
#1 is TDC, the spark plug has fired, combustion has/is taken place and the piston is starting its power stroke, both valves closed.
#6 would be at 240 degrees, both valves are closed and it is on its compression stroke.
#2 would be at 120 degrees, and on the intake stroke with the intake valve open.
#4 would be at TDC, valve overlap (which is where cam timing is set), and it has just completed its exhaust stroke and begining its intake stroke. with most cams, both valve are slightly open with the exhaust closing and the intake opening.
#3 is at 240 degrees and on the exhaust stroke. exhaust open.
#5 is at 120 degrees nearing the bottom of its power stroke, both valves closed.

hope this helps.
start at TDC and work CCW in firing order.

T77,
exactly what i was looking for....i guess i could have figured it out, thanks for helping me save my few remaining grey cells! let's close the thread.
thanks again and regards , ben

[HawgRyder]

Internal Combustion Engine.....Suck...Squeeze...Bang...Blow.
And there you have it.
Bob

[db_cooper]

Combustion Chamber - YouTube

Whats missing from the video is the scavenge stroke..