rocker arms
#11
03-07-2011, 12:52 PM
What I can understand is a "percieved" increase in the duration due to the valve opening faster. If the valve opens faster (which it would have to due to the ratio increase) then the gasses comming in and out would have a little more time to be effective, thus making is seem like the druation is increased. But mechanicly I cant see how it could increase without redesigning the cam's profile.
Massey
Massey
#12
03-07-2011, 12:55 PM
disagree. the time open is not affected by lift. the opening will be larger at any given point in time, but the time between completely open to completely shut is exactly the same per revolution of the engine.
#13
03-07-2011, 01:00 PM
I never said the time was changed, just the perception was changed. The valve will open faster and close faster but not for a longer period. This will allow more air in sooner due to the increase in the lift at any given point. There is no mechanical change but there is an effective change in the valve opening faster. That is why I said "percieved" duration.
Does that make sense?
Massey
Does that make sense?
Massey
#14
03-07-2011, 01:07 PM
What I can understand is a "percieved" increase in the duration due to the valve opening faster. If the valve opens faster (which it would have to due to the ratio increase) then the gasses comming in and out would have a little more time to be effective, thus making is seem like the druation is increased. But mechanicly I cant see how it could increase without redesigning the cam's profile.
Massey
Massey
#15
03-07-2011, 01:09 PM
I think i know what u mean. but that is much closer to an increase in lift than in duration. (actually... it IS an increase in lift)
both things will allow more air in, but the difference is in air/unit time vs. total time.
duration affects total time, lift affects air/unit time.
Changing the rocker is the same thing as swapping out your cam for one with the same duration but a small increase in lift. would you apply your above statement to a situation like this cam swap?
both things will allow more air in, but the difference is in air/unit time vs. total time.
duration affects total time, lift affects air/unit time.
Changing the rocker is the same thing as swapping out your cam for one with the same duration but a small increase in lift. would you apply your above statement to a situation like this cam swap?
#16
03-07-2011, 01:11 PM
I kinda figured that so I tried to explain it differently. It is all good. I agree with you 100% you cant change the mechanics of the cam with the rocker. Now a different size roller on the lifter could cause a duration change but I have never heard of some one redesigning lifters to make for a longer duration... Too expensive.
Massey
Massey
#17
03-07-2011, 03:35 PM
see what I started...............
if you measure at 50 then yes, but, since the valves are open sooner then it does slightly change duration. I'm heading out but I will find the graph. I don't make up these things because I too simply thought it was lift. Now I'm not saying that you'll get noticable duration change and it's an alternative to a cam swap.
if you measure at 50 then yes, but, since the valves are open sooner then it does slightly change duration. I'm heading out but I will find the graph. I don't make up these things because I too simply thought it was lift. Now I'm not saying that you'll get noticable duration change and it's an alternative to a cam swap.
#18
03-07-2011, 04:20 PM
Join Date: Oct 2007
Location: The 'Burbs of Chicago
Posts: 18,306
quick question about this:
in 1.5 rockers, is the 1.5 a result of the ratio between the distance between the pushrod contact point and the rocker bolt and the distance from the rocker bolt to the spring cap contact point?
(pushrod to center/center to spring). If so then your calculation makes sense. But i was under the impression that the rocker was a direct measurement either of the arm distance or something like that. If so then the actual lobe lift couldnt be calculated from the numbers given. I have seen similar calcs done, but never calling the .334 number the actual lobe lift. usually they refer to a stock setup with the 1.5 rocker, and then do a ratio calculation to find new lift. i.e. if lift was .500 with a stock 1.5 rocker, the lift would be .500*(1.6/1.5)=.534 with a 1.6. but this calculation uses the ratio in a way that skips any actual cam measurements.
I honestly dont know either way. I just wanted to bring up how I have seen this done in the past
in 1.5 rockers, is the 1.5 a result of the ratio between the distance between the pushrod contact point and the rocker bolt and the distance from the rocker bolt to the spring cap contact point?
(pushrod to center/center to spring). If so then your calculation makes sense. But i was under the impression that the rocker was a direct measurement either of the arm distance or something like that. If so then the actual lobe lift couldnt be calculated from the numbers given. I have seen similar calcs done, but never calling the .334 number the actual lobe lift. usually they refer to a stock setup with the 1.5 rocker, and then do a ratio calculation to find new lift. i.e. if lift was .500 with a stock 1.5 rocker, the lift would be .500*(1.6/1.5)=.534 with a 1.6. but this calculation uses the ratio in a way that skips any actual cam measurements.
I honestly dont know either way. I just wanted to bring up how I have seen this done in the past
http://www.compcams.com/Company/CC/c...?csid=107&sb=2
#19
03-07-2011, 06:07 PM
see what I started...............
if you measure at 50 then yes, but, since the valves are open sooner then it does slightly change duration. I'm heading out but I will find the graph. I don't make up these things because I too simply thought it was lift. Now I'm not saying that you'll get noticable duration change and it's an alternative to a cam swap.
if you measure at 50 then yes, but, since the valves are open sooner then it does slightly change duration. I'm heading out but I will find the graph. I don't make up these things because I too simply thought it was lift. Now I'm not saying that you'll get noticable duration change and it's an alternative to a cam swap.
