Direct correlation between cam duration and powerband?
08-22-2004, 01:40 AM
#1
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Direct correlation between cam duration and powerband? Lately I've been wondering how cam companies arrive at the 'useful powerband' or 'useful RPM' range of values they quote with their cams. It seems that the longer/higher the duration, the higher up the powerband usable power comes on. Is this correct?
For example, Comp advertises the 'operating range' of some of their split duration 'RPM' camshafts as follows:
206/212: 800-5800 RPM's
212/218: 1200-6000 RPM's
216/220: 1200-6000 RPM's
220/224: 1600-6600 RPM's
224/228: 2000-6800 RPM's
228/230: 2200-7200 RPM's
...and so on.
The reason I am asking is this - while the low torque placement of a 206/212 appeals to me (as a heavy truck owner), I don't necessarily like that it runs out of gas at around 5800 RPM's. I'd like my cam to go up to 6000, 6200, or perhaps a little higher. If this is the case, can I assume that if I get a 208/214, that my powerband will move to 1000-6000 RPM's or somewhere thereabouts?
For example, Comp advertises the 'operating range' of some of their split duration 'RPM' camshafts as follows:
206/212: 800-5800 RPM's
212/218: 1200-6000 RPM's
216/220: 1200-6000 RPM's
220/224: 1600-6600 RPM's
224/228: 2000-6800 RPM's
228/230: 2200-7200 RPM's
...and so on.
The reason I am asking is this - while the low torque placement of a 206/212 appeals to me (as a heavy truck owner), I don't necessarily like that it runs out of gas at around 5800 RPM's. I'd like my cam to go up to 6000, 6200, or perhaps a little higher. If this is the case, can I assume that if I get a 208/214, that my powerband will move to 1000-6000 RPM's or somewhere thereabouts?
08-22-2004, 03:58 AM
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Duration is the primary spec that one would use to determine where the powerband will be. There should be no question or doubts about it.
I just installed the 206/212 cam on a 112 icl (2 deg retarded). I needed to increase my shift points a little to obtain better ET & mph at the drag strip. That means the upper power range INCREASED over stock. Hope this helps.
I just installed the 206/212 cam on a 112 icl (2 deg retarded). I needed to increase my shift points a little to obtain better ET & mph at the drag strip. That means the upper power range INCREASED over stock. Hope this helps.
08-23-2004, 12:27 AM
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Originally Posted by Naked AV
206/212: 800-5800 RPM's
212/218: 1200-6000 RPM's
216/220: 1200-6000 RPM's
220/224: 1600-6600 RPM's
224/228: 2000-6800 RPM's
228/230: 2200-7200 RPM's
...and so on.
The reason I am asking is this - while the low torque placement of a 206/212 appeals to me (as a heavy truck owner), I don't necessarily like that it runs out of gas at around 5800 RPM's. I'd like my cam to go up to 6000, 6200, or perhaps a little higher. If this is the case, can I assume that if I get a 208/214, that my powerband will move to 1000-6000 RPM's or somewhere thereabouts?
212/218: 1200-6000 RPM's
216/220: 1200-6000 RPM's
220/224: 1600-6600 RPM's
224/228: 2000-6800 RPM's
228/230: 2200-7200 RPM's
...and so on.
The reason I am asking is this - while the low torque placement of a 206/212 appeals to me (as a heavy truck owner), I don't necessarily like that it runs out of gas at around 5800 RPM's. I'd like my cam to go up to 6000, 6200, or perhaps a little higher. If this is the case, can I assume that if I get a 208/214, that my powerband will move to 1000-6000 RPM's or somewhere thereabouts?
08-23-2004, 09:01 AM
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That is true marc-w, but you have to increase the exhaust to keep up with the intake.If I was putting a cam in a truck I"d be more concerned with power from idle to say 4500, lets face it thats where you'll spend 90% of driving.More like idle to3000,get small duration with fair amount of lift say 550 to 575.Don"t know about lda, seems Comp makes their lower rpm cams with a tighter LDA.Also believe ICL would be critical to low rpm performance say from 110 to 107 as the lower ICL would close the intake sooner making more cylinder pressure so more torque.This could all be calculated in advance by figuring out overlap,and how you want your valve timing to be. 
08-23-2004, 09:16 AM
#7
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If you look at the cam thread we discuss valve events, which affect where the powerband happens at.
If you look at the CFM thread you can see some "ghetto math" on how to determine CFM/vs RPM requirements.
https://ls1tech.com/forums/generation-iii-internal-engine/163744-camshaft-discussion-cfm-requirements-rpm.html
This is from Erik @ HPE
If you look at the CFM thread you can see some "ghetto math" on how to determine CFM/vs RPM requirements.
https://ls1tech.com/forums/generation-iii-internal-engine/163744-camshaft-discussion-cfm-requirements-rpm.html
This is from Erik @ HPE
Well you can ghetto figure it as (346/2)CID*6800RPM/1728 CID per one Cubic Foot= air engine takes in at that RPM at 100 % VE or 680 CFM.
Now we see there are 8 cylinders so 680/8 = 85 CFM per cylinder but.......
The cylinder is only open say in a heads cam car for 224 out of the 720 degrees of the 4 cycle engine so it's only open .311111 of the cycle or roughly 31 % of the time in this case.
The actual airflow therefore has to occur during the short time the piston is traveling DOWN the bore and the little extra time it has before velocity is overcome by rising cylinder pressure from the upward motion of the rising piston in the bore.
85/.311111=273cfm average during this shorter but real period of intake port flow.
I could run MORE cam and slow the air down by running a longer duration cam but at some point the cam will both open too early on the exhaust stroke and close too late on the intake stroke so yes there are limits. Cams over 280 are getting more and more rare in racing as heads have gotten better and better.
Now we see there are 8 cylinders so 680/8 = 85 CFM per cylinder but.......
The cylinder is only open say in a heads cam car for 224 out of the 720 degrees of the 4 cycle engine so it's only open .311111 of the cycle or roughly 31 % of the time in this case.
The actual airflow therefore has to occur during the short time the piston is traveling DOWN the bore and the little extra time it has before velocity is overcome by rising cylinder pressure from the upward motion of the rising piston in the bore.
85/.311111=273cfm average during this shorter but real period of intake port flow.
I could run MORE cam and slow the air down by running a longer duration cam but at some point the cam will both open too early on the exhaust stroke and close too late on the intake stroke so yes there are limits. Cams over 280 are getting more and more rare in racing as heads have gotten better and better.
