Hey,

Ok, I know what lift and duration both mean by definition and I understand the concepts but as far as analyzing one set of cams compared to another, I'm lost.

For example skunk2 stage 2's are:

IN. 0.485, 266
EX. 0.466, 262

Can you explain what those numbers mean and how I should use them to compare cams?

Thanks

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by litterbox &raquo;</TD></TR><TR><TD CLASS="quote">Hey,

Ok, I know what lift and duration both mean by definition and I understand the concepts but as far as analyzing one set of cams compared to another, I'm lost.

For example skunk2 stage 2's are:

IN. 0.485, 266
EX. 0.466, 262

Can you explain what those numbers mean and how I should use them to compare cams?

Thanks</TD></TR></TABLE>

Duration is the number of degrees (out of 360 total) that a lobe of the camshaft is acting upon the valve(s) it controls.

Lift is the maximum distance traveled, usually in inches, of the listed valve(s).

Duration keeps the valves open for longer, thus increasing cylinder volume per cycle and, as a result, power output. The downside to duration is that when you gain too much of it, you get a rough idle and shitty gas mileage.

Enough duration on the intake and exhaust sides of the camshaft(s) creates overlap. Overlap is, as it would suggest, when the intake and exhaust valves are being acted upon in the same reference frame. Overlap shifts your powerband higher - generally - and often times results in post-combustion or "backfire". The physics behind overlap is something like this: if the exhaust valves are open when the intake valves are open, the pressure differential from the atmosphere side of the exhaust will help "suck" or "jam" air in from the intake side. Unfortunately, because so much of a good idle depends upon vacuum retention, overlap can all but slay your idle completely and will devastate gas mileage.

Of course, the above is referencing high-overlap applications.

Lift is a simple y-axis movement of the valve. For the most streetable results, maximize lift and optimize cam timing without dialing in too much overlap.



EDIT: Furthermore, when comparing camshafts, the one that will net you the most performance "out of the box" is usually the one with the largest lift and duration figures, however, a less aggressive camshaft can make significantly more power with proper tuning than a more aggressive camshaft with no tuning whatsoever.

Also, it is important to remember that the camshaft is basically the heart of your engine, dictating the biorhythm (for lack of a better word) of the interdependent parts. As such, you should choose a bumpstick that compliments your previously added parts. If you want top end performance and you've already bought a large-plenum intake manifold and longtube 4-1 header, you might want to see more overlap and slightly less lift out of your camshaft so your gas mileage doesn't go completely to **** while getting great performance.

<u>Gestalt</u>. Look it up. Modify accordingly.

 

Thanks for the clear explanation Archidictus.

So now if we go back to the example of the skunk2 specs:

IN. 0.485, 266
EX. 0.466, 262

This means that IN valves are pushed up 0.485inches and open for 266degrees of the cam's lobe? Is that right?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by litterbox &raquo;</TD></TR><TR><TD CLASS="quote">Thanks for the clear explanation Archidictus.

So now if we go back to the example of the skunk2 specs:

IN. 0.485, 266
EX. 0.466, 262

This means that IN valves are pushed up 0.485inches and open for 266degrees of the cam's lobe? Is that right?</TD></TR></TABLE>

This means that the intake valve will be moved away from the surface of the combustion chamber a total of .485 inches at max lift, yes. The duration figure of 266 degrees tells us that for 266 of the camshaft's 360 degree turn, it will be acting upon the valve. That's a healthy duration.

If you can find the activation point (xx degrees past TDC, for example) for both the intake and exhaust lobes, you can do some simple math and figure out the overlap .

 

Crystal.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Archidictus &raquo;</TD></TR><TR><TD CLASS="quote">

Duration is the number of degrees (out of 360 total) that a lobe of the camshaft is acting upon the valve(s) it controls.

Lift is the maximum distance traveled, usually in inches, of the listed valve(s).

Duration keeps the valves open for longer, thus increasing cylinder volume per cycle and, as a result, power output. The downside to duration is that when you gain too much of it, you get a rough idle and shitty gas mileage.

Enough duration on the intake and exhaust sides of the camshaft(s) creates overlap. Overlap is, as it would suggest, when the intake and exhaust valves are being acted upon in the same reference frame. Overlap shifts your powerband higher - generally - and often times results in post-combustion or "backfire". The physics behind overlap is something like this: if the exhaust valves are open when the intake valves are open, the pressure differential from the atmosphere side of the exhaust will help "suck" or "jam" air in from the intake side. Unfortunately, because so much of a good idle depends upon vacuum retention, overlap can all but slay your idle completely and will devastate gas mileage.

Of course, the above is referencing high-overlap applications.

Lift is a simple y-axis movement of the valve. For the most streetable results, maximize lift and optimize cam timing without dialing in too much overlap.



EDIT: Furthermore, when comparing camshafts, the one that will net you the most performance "out of the box" is usually the one with the largest lift and duration figures, however, a less aggressive camshaft can make significantly more power with proper tuning than a more aggressive camshaft with no tuning whatsoever.

Also, it is important to remember that the camshaft is basically the heart of your engine, dictating the biorhythm (for lack of a better word) of the interdependent parts. As such, you should choose a bumpstick that compliments your previously added parts. If you want top end performance and you've already bought a large-plenum intake manifold and longtube 4-1 header, you might want to see more overlap and slightly less lift out of your camshaft so your gas mileage doesn't go completely to **** while getting great performance.

<u>Gestalt</u>. Look it up. Modify accordingly.</TD></TR></TABLE>

well said

 

Wow that sucks, I didnt know that camshafts were that complicated to pick out. I just read your re: post and I am mind boggled. So, what about when going to a shop and have it done, would it be better to go to the manufacturer itself (skunk2 is only 15 min from my house ), or to a trusted mechanic....I am trying to go all motor but have no experience building the top/bottom ends.....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bee18Hatch &raquo;</TD></TR><TR><TD CLASS="quote">Wow that sucks, I didnt know that camshafts were that complicated to pick out. I just read your re: post and I am mind boggled. So, what about when going to a shop and have it done, would it be better to go to the manufacturer itself (skunk2 is only 15 min from my house ), or to a trusted mechanic....I am trying to go all motor but have no experience building the top/bottom ends.....</TD></TR></TABLE>
its not as easy as some think..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bee18Hatch &raquo;</TD></TR><TR><TD CLASS="quote">Wow that sucks, I didnt know that camshafts were that complicated to pick out. I just read your re: post and I am mind boggled. So, what about when going to a shop and have it done, would it be better to go to the manufacturer itself (skunk2 is only 15 min from my house ), or to a trusted mechanic....I am trying to go all motor but have no experience building the top/bottom ends.....</TD></TR></TABLE>

I would suggest going to a shop with a good reputation. The questions you need to ask yourself are:

1.) how able is my cylinder head to deal with the punishment of a high-lift and long-duration camshaft

2.) what is my compression and how will it compliment the cam's profile

3.) how much money do I have for tuning and fuel/spark system modifications to make my allmotor project safe.

Once you have these dialed in you should be able to work with a reputable shop to find the camshaft that is perfect for your goals.

 

man sorry i had to resurrect this old thread. i'm so glad i readed this. it was the best info i've read in a while and better than make a new thread.