Duration Vs. Lift on NA Motor
Originally Posted by Old SStroker
Perhaps turbulent wasn't exactly the correct word, but it paints a picture. Let's say on the flow bench the flow increases steadily with increasing valve lift with a smooth sound until the ~.600 point where the flow virtually stops increasing and the sound in the port changes indication the air is not "happy". You might describe this as "chaotic" flow. If it's chaotic on the steady-state flow bench, picture what it is in a cycling engine.
I interpreted 12secSS's post to mean this. If you lift the valve into this chaotic flow regime, there is a good chance the engine won't like it. It does present a challenge to getting more air in. "Fixing the port" is not always possible.
Jon
I interpreted 12secSS's post to mean this. If you lift the valve into this chaotic flow regime, there is a good chance the engine won't like it. It does present a challenge to getting more air in. "Fixing the port" is not always possible.
Jon
When I came up with my cam I looked at several things. At the time there were not a lot of cars running the way I wanted too, and had heads that flowed what mine do. So I found the closest engine type that did. The 302 ford. It has a 4in bore and heads that flow in the 330 range with similar runner size. So I looked at Renegade spec cam's and based my choice on those. As for LSA I went from personal experience. I herd a 110 will not work on a power adder car, yet when we switched the same came specs from a 114, 112, then a 110 it was a whole new power curve. We went from slow with a 114 to on the bumper with the 110. N/A the car was allot faster too. As for the lift I flowed my heads with the intake and TB attached and went with the lift point that flowed the most plus .030 to compensate for bleed down and flexing of the push rods. When I ordered the cam they asked if I was sure this wasn't a solid roller cam lol. I still hear people try to say I'm over camed until the see my E.T's.
On The Tree
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From: Portsmouth, VA
Originally Posted by PowerShift408
I've always wondered why Gen 3 cams were big on lift, lower on duration as compared to say, a Gen 1 cam, which has very little lift even compared to our smaller cams, but waayy more duration.
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From: Upstate NY
Originally Posted by ONEBADWS6
When I came up with my cam I looked at several things. At the time there were not a lot of cars running the way I wanted too, and had heads that flowed what mine do. So I found the closest engine type that did. The 302 ford. It has a 4in bore and heads that flow in the 330 range with similar runner size. So I looked at Renegade spec cam's and based my choice on those. As for LSA I went from personal experience. I herd a 110 will not work on a power adder car, yet when we switched the same came specs from a 114, 112, then a 110 it was a whole new power curve. We went from slow with a 114 to on the bumper with the 110. N/A the car was allot faster too. As for the lift I flowed my heads with the intake and TB attached and went with the lift point that flowed the most plus .030 to compensate for bleed down and flexing of the push rods. When I ordered the cam they asked if I was sure this wasn't a solid roller cam lol. I still hear people try to say I'm over camed until the see my E.T's.
Originally Posted by Old SStroker
Perhaps turbulent wasn't exactly the correct word, but it paints a picture. Let's say on the flow bench the flow increases steadily with increasing valve lift with a smooth sound until the ~.600 point where the flow virtually stops increasing and the sound in the port changes indication the air is not "happy". You might describe this as "chaotic" flow. If it's chaotic on the steady-state flow bench, picture what it is in a cycling engine.
I interpreted 12secSS's post to mean this. If you lift the valve into this chaotic flow regime, there is a good chance the engine won't like it. It does present a challenge to getting more air in. "Fixing the port" is not always possible.
Jon
I interpreted 12secSS's post to mean this. If you lift the valve into this chaotic flow regime, there is a good chance the engine won't like it. It does present a challenge to getting more air in. "Fixing the port" is not always possible.
Jon
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From: Upstate NY
Originally Posted by Ari G
ok le´t say the peak flow is at 600lift,Do enginebuilders make the lift a bit higher 20-25% to get the peak flow twice in the event?And how is that a benefit?
I suspect you see that as a problem. What are the alternatives to get more air into the engine?
Jon
Originally Posted by Old SStroker
All I'm saying is that IF the flow goes "chaotic" at some lift point, liftiing the valve beyond that point, (.720-.750 in your example) might not be the wisest thing to do.
I suspect you see that as a problem. What are the alternatives to get more air into the engine?
Jon
I suspect you see that as a problem. What are the alternatives to get more air into the engine?
Jon
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From: Upstate NY
Originally Posted by Ari G
I was just asking if this is true(20-25%) and why it is done
As to how much above the max flow point to lift the valve, that might depend on how much area under the lift curve the engine designer wants. I suggest that the 20-25% you quoted might be high.
Thought experiment:
1) assume that flow maxes at .600 on the flow bench and basically holds there up to .750. This doesn't happen too often.
2) lifting the valve to .750 results in problems with springs and things.
2) what else could you do to keep the valve in the max flow regime for the number of degrees of duration needed to get the air you need and still maintain the IVO and IVC points that are best for the engine? (That's back to my previous post)
Your turn...
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From: Naperville, IL
Originally Posted by Old SStroker
Assuming the flow doesn't get chaotic above say .600 but it just stops increasing on the flow bench, increasing the max lift above the max flow point allows the flow to be at the max for a number of degrees. That will obviously allow more air in.
As to how much above the max flow point to lift the valve, that might depend on how much area under the lift curve the engine designer wants. I suggest that the 20-25% you quoted might be high.
Thought experiment:
1) assume that flow maxes at .600 on the flow bench and basically holds there up to .750. This doesn't happen too often.
2) lifting the valve to .750 results in problems with springs and things.
2) what else could you do to keep the valve in the max flow regime for the number of degrees of duration needed to get the air you need and still maintain the IVO and IVC points that are best for the engine? (That's back to my previous post)
Your turn...
As to how much above the max flow point to lift the valve, that might depend on how much area under the lift curve the engine designer wants. I suggest that the 20-25% you quoted might be high.
Thought experiment:
1) assume that flow maxes at .600 on the flow bench and basically holds there up to .750. This doesn't happen too often.
2) lifting the valve to .750 results in problems with springs and things.
2) what else could you do to keep the valve in the max flow regime for the number of degrees of duration needed to get the air you need and still maintain the IVO and IVC points that are best for the engine? (That's back to my previous post)
Your turn...
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From: Upstate NY
Originally Posted by Asmodeus
I'll guess.. you'd want more agressive lobe profiles to get the valve off the seat faster, and increase duration at lower lifts?
I would say that you would want a lobe on your cam that is more "flat" on top, for lack of a better term. Am I even partly close??
You may want the cam to come off of the seat slower, but really become aggressive after ~.200 lift?? And then more or less stall out at around .650 or somewhere close.
You may want the cam to come off of the seat slower, but really become aggressive after ~.200 lift?? And then more or less stall out at around .650 or somewhere close.
Originally Posted by Old SStroker
Max flow isn't at lower lifts. Low lift flow may hurt rather than help a highend engine.
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From: Naperville, IL
Originally Posted by Old SStroker
Max flow isn't at lower lifts. Low lift flow may hurt rather than help a highend engine.
Off topic a bit because I'm a cam newbie.. With heads aimed at good low-mid lift flow, and a lobe profile with an agressive ramp, would I want to then close the intake valve a little sooner to prevernt reversion? Or is that just a band-aid?
Originally Posted by DrkPhx
David Vizard wrote a real good article about cams that was specific to the LS1 a couple of years ago in GMHTP.
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From: Upstate NY
Originally Posted by Stang's Bane
I would say that you would want a lobe on your cam that is more "flat" on top, for lack of a better term. Am I even partly close??
You may want the cam to come off of the seat slower, but really become aggressive after ~.200 lift?? And then more or less stall out at around .650 or somewhere close.
You may want the cam to come off of the seat slower, but really become aggressive after ~.200 lift?? And then more or less stall out at around .650 or somewhere close.
Unfortunately you probably can't do it just with parts from Jegs.
Originally Posted by PowerShift408
I've always wondered why Gen 3 cams were big on lift, lower on duration as compared to say, a Gen 1 cam, which has very little lift even compared to our smaller cams, but waayy more duration.
Originally Posted by chae
Anyone have a link to this article or does anyone know which issue it was in? Thanks for your help.
Back in post #5.
