camshaft duration question

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lil red

lil red

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looking for a bit of clarity, amidst the confusion of trying to understand camshaft duration....
Anyway, I understand that an accurate comparison of camshaft durations between manufacturers should be done at.050" lift, but is the difference in advertised duration a result of a different camshaft profile/curve, or is it because its measured at a different point when it moves of the base circle, like at ..002",.003", .006" or so?
for example the following 2 camshafts -
Lunati voodoo - 268*/276* and 226*/234* at .050" 1800 -6200 rpm
Howards - 273*/277* and 226*/230* 2200-6000 rpm

the lunati is 494/513 lift, the howards 525/531 and both 106 ICL

A 'step' in camshaft size is about 5* , so according to the duration at .050" these camshafts should be roughly the same size, correct?
Both are 226* at .050", however there is 5 deg. difference at the ad. duration
 
lil red said:
looking for a bit of clarity, amidst the confusion of trying to understand camshaft duration....
Anyway, I understand that an accurate comparison of camshaft durations between manufacturers should be done at.050" lift, but is the difference in advertised duration a result of a different camshaft profile/curve, or is it because its measured at a different point when it moves of the base circle, like at ..002",.003", .006" or so?
for example the following 2 camshafts -
Lunati voodoo - 268*/276* and 226*/234* at .050" 1800 -6200 rpm
Howards - 273*/277* and 226*/230* 2200-6000 rpm

the lunati is 494/513 lift, the howards 525/531 and both 106 ICL

A 'step' in camshaft size is about 5* , so according to the duration at .050" these camshafts should be roughly the same size, correct?
Both are 226* at .050", however there is 5 deg. difference at the ad. duration
Click to expand...
Yep. So the cam grinders are on the same playing field, the @.050 measurement is more constant. With the two cams being close to the same duration, The lift is where the higher rpm comes from. The Howards cam has some pretty fast lobes compared to the Lunati. It goes from a little lift @.050 to .525/.531 in the same time that the Lunati gets to a little over .500 lift.
 
yellow rose said:
The Howard's lobes are slower.

The answer is more complicated than that, but that's the short answer.
Click to expand...
Does my analogy make any sense then? I would think the Howards lobes were faster because they both start at relatively the same spot and open the valve for the same length of time but the Howards cam opens the valve further. I'm cornfused! LOL
 
There is a lot that goes into cam lobes and the short answer is it is complicated, as YR said in his post. Everyone uses a different formula for advertised. .050 is informative but is not your silver bullet. There are opening ramps, closing ramps, pressure loads, smooth profiles, and that is just some variables.
 
toolmanmike said:
Does my analogy make any sense then? I would think the Howards lobes were faster because they both start at relatively the same spot and open the valve for the same length of time but the Howards cam opens the valve further. I'm cornfused! LOL
Click to expand...

if the howards cam is faster, does that account for the larger advertised duration? does faster mean a faster rate of lift. With a higher lift on the howards camshaft, and the rpm moved up compared to the voodoo, the sweet spot would also move up affected by lift correct? (even though the cams are the same 'size')
 
The sweet spot will mainly be dependent on which engine or engines with what heads.
A 273 vs 340 with those cams will have way different sweet spots same with a 340 with X heads or fully ported W2 heads way different outcomes. Those sweet spots are probably based on what they think the average guy would that cam in, some kind of a 360 combo of their choosing, not really apples to apples.
 
lil red said:
looking for a bit of clarity, amidst the confusion of trying to understand camshaft duration....
Anyway, I understand that an accurate comparison of camshaft durations between manufacturers should be done at.050" lift, but is the difference in advertised duration a result of a different camshaft profile/curve, or is it because its measured at a different point when it moves of the base circle, like at ..002",.003", .006" or so?
for example the following 2 camshafts -
Lunati voodoo - 268*/276* and 226*/234* at .050" 1800 -6200 rpm
Howards - 273*/277* and 226*/230* 2200-6000 rpm

the lunati is 494/513 lift, the howards 525/531 and both 106 ICL

A 'step' in camshaft size is about 5* , so according to the duration at .050" these camshafts should be roughly the same size, correct?
Both are 226* at .050", however there is 5 deg. difference at the ad. duration
Click to expand...

lil red said:
if the howards cam is faster, does that account for the larger advertised duration? does faster mean a faster rate of lift. With a higher lift on the howards camshaft, and the rpm moved up compared to the voodoo, the sweet spot would also move up affected by lift correct? (even though the cams are the same 'size')
Click to expand...


You also have to look at lobe separation which for both is 110°...

Since both cams are ground on the same lobe centers, with the same intake center line, then with the larger advertised duration of the Howards will have more overlap and be a little choppier...

The Lunati has a faster ramp from .000 - .050 because it has lower advertised duration than the Howards... So it is covering the same lift in less duration - 268°/276° Lunati vs 273°/277° Howards...

Howards has a faster ramp from .050" to max lift because it has more lift than the Lunati at pretty much the same duration from .050"...

Keep in mind that the faster you close the valve, the higher the force on the valve and seat... So a faster ramp on the .000 - .050" will close faster with more force and wear on the seats - translation it will beat up the seats more with a faster ramp...

So with Howards having the slower ramp for opening and closing will be more friendly on your valves and seats for more durability.... The Howards will have a little more overlap and be a little rougher idle than the Lunati...

You will also have to run the proper valve springs and have your head guy make sure there is enough travel in the valve so you don't spring bind or bottom out the valve and break a valve... Any lift over .500 will need this checked and also check piston to valve clearance when you install it so a valve doesn't hit a piston which can put a hole in the block....
 
Plus a grinder can take a popular .050 cam spec, and put an advertised on it that makes it sound 3 sizes bigger when it's idling.
or conversely, snap it open so fast that the only way to keep it all together is with hi spring pressures.
Or they can just give you an advertised number from a different starting point.
Take the ever-popular 222@.050cam.
On the very same cam,it might measure as a 268 @.006, or a 264@ 008, or a 262@.010.
Or somebody could sell you a 270 cam and NOT tell you that it's a 270 @.008,and so, might be a 274@.006. Then He can tell you that his 270 will make more power than anybody else's 270. And maybe it will, cuz it's not a 270, when measured the same way as everybody else is measuring,namely at .006; but rather a 274. But if it doesn't, at least it will sound like it might.lol
Or someone could sell you a 222@.050 cam that has 70 degrees of ramps, making it a 292 advertised;Yet for 40*,or more, of those 70, it is slowly closing the intake and bleeding cylinder pressure back into the intake so the idle sounds like a top-fuel car. Hmmm Yeah I call that a poser cam.
But one thing that is almost for sure;among street 222@.050 cams, the one that has the highest lift, will likely have the fastest lobes on it, and will require the highest springing, and don't even care about the advertised, cuz the grinder will engineer the ramps to make sure his cam has a reasonable life-span with those springs. Then you the builder will set the Scr to work with those ramps, and stay within the working limits of the chosen fuel.
So a street cam, will end up completely different from a race cam. A street cam may have to endure 100,000 miles, and get 4 oil changes per year. Whereas a race cam has a lifespan measured 1/4 mile atta time,usually gets plenty of fresh oil, and it just gets swapped out as required.
 
Last edited:
273 said:
The sweet spot will mainly be dependent on which engine or engines with what heads.
A 273 vs 340 with those cams will have way different sweet spots same with a 340 with X heads or fully ported W2 heads way different outcomes. Those sweet spots are probably based on what they think the average guy would that cam in, some kind of a 360 combo of their choosing, not really apples to apples.
Click to expand...
yeah your right, didn't really think that out before i typed, sorry
but comparing identical engines with each cam...
 
krazykuda said:
You also have to look at lobe separation which for both is 110°...

Since both cams are ground on the same lobe centers, with the same intake center line, then with the larger advertised duration of the Howards will have more overlap and be a little choppier...

The Lunati has a faster ramp from .000 - .050 because it has lower advertised duration than the Howards... So it is covering the same lift in less duration - 268°/276° Lunati vs 273°/277° Howards...

Howards has a faster ramp from .050" to max lift because it has more lift than the Lunati at pretty much the same duration from .050"...

Keep in mind that the faster you close the valve, the higher the force on the valve and seat... So a faster ramp on the .000 - .050" will close faster with more force and wear on the seats - translation it will beat up the seats more with a faster ramp...

So with Howards having the slower ramp for opening and closing will be more friendly on your valves and seats for more durability.... The Howards will have a little more overlap and be a little rougher idle than the Lunati...

You will also have to run the proper valve springs and have your head guy make sure there is enough travel in the valve so you don't spring bind or bottom out the valve and break a valve... Any lift over .500 will need this checked and also check piston to valve clearance when you install it so a valve doesn't hit a piston which can put a hole in the block....
Click to expand...
ah , makes sense, thank you, very good explanation
 
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