In this pic, we are looking at the front end of the camshafts: The A cam is on the left; the T cam is on the right.
I have rotated the cams to make it easier to actually look at the cam lobes; in order to compare their size and shape. The lobes that are upright in front are the exhaust lobes for number 1 cylinder.
Lobe shape and size, often called the lobe profile, controls what happens and when, as far as the opening and closing of the valve. The "when" and the "how much" (how far/how fast) of valve openings and closings have a great impact on the engine's performance. I want to find out what those "when's" and "how much's" are.
Just looking at the lobes on the two camshafts shows that the shapes of the lobes are similar; and it is obvious that the A cam lobe is a bit "taller" as well as "fatter". We'll see how similar and how different they are...
Test conditions:
...a 530 cylinder head in very good uncut, unwarped condition.
...camshafts tested are both in good used conditioned; cleaned and measured for wear. The wear measured was less than 0.001in for all lobes on all cams measured and tested: two T's and one A.
...the valves used in the cylinder head, as well as the other valvetrain components used, were cleaned and measured and inspected for any defects or variations.
...the valve springs used were CompCams valve test springs.
...the degree wheel is a 7in metal degree wheel; and was indexed to and mounted on a modified volvo cam gear.
...no rubber dampers were installed on the valve stems; to insure accurate clearance adjustment.
...valve clearance was set to 0.014in for both intake and exhaust valves; on all camshafts tested.
What I wanted to know:
...maximum valve lift
...actual valve lift
...valve duration [how long, measured in degrees of crankshaft rotation, the valve is open] and measured using 0.020in valve opening as the starting and ending points of duration.
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SIDEBAR FOOTNOTE:
I used the 0.020in valve opening as the lift point to measure duration because there is a general consensus that at less than 0.020in of valve opening, there is not any "effective" flow. [this is debatable and arguable; as is what the SAE J-604 spec for tappet lift actually IS.
In American aftermarket camshaft listings, duration is usually listed two ways:
...as the duration of valve opening based on 0.050in valve lift.
...as "advertised duration"...based on the J-604 spec.
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AND EVEN THAT CAN BE CONFUSING!!!
How so??? Tappet lift, or movement, can be quite different from valve lift, or movement. Tappets are in contact directly with the cam lobes. The valves may not be so directly connected. The valves can have intermediary components between them and the cam lobes that alter the cam lobes effect. A rocker arm is just such a device: it multiplies the tappet movement; commonly in the 1.5:1 ratio; where the tappet movement is increased by 50% at the valve.
But not all rocker arms are 1.5:1 ratio multipliers. To try to minimize the confusion, and to attempt to "standardize" the definition of duration, the SAE J-604 spec was developed; defining duration as occurring from X number of thousandths of an inch of "tappet" lift.
In spite of the SAE effort, people play around with that specification; and fudge the spec to their advantage or purpose.
The "duration at 0.050in valve opening" was another attempt to standardize cam specs for comparison purposes. It is helpful; but not perfectly so. The rocker arm ratio used in the valvetrain when measuring that camshaft will affect the validity, or true comparability, of that specification. And, people play around with that as well.
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For "Maximum Valve Lift", I used a dial indicator on the camlobes directly, to measure the total lift possible.
For "Actual Valve Lift", I used a dial indicator at the valve head, in the combustion chamber, to measure the actual lift of the valve. No fudging; no games; no tricks. I wanted to see it like the combustion chamber sees it: that is where the action is at.
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Advertised duration is very close to "total" duration, because the J spec calls for some movement at the tappet...at least a couple of thou.
My use of the term "total duration" means the duration from the point that the valve starts to open to the point that the valve closes: the TOTAL duration.
Further in this discussion, I bring up an observation about the clearance ramps of the cam lobes possibly having an impact on the camshaft's performance. And part of that ties into the 0.020in valve lift amount possibly affecting the mushroom effect onset.
Because of that, I have decided to stick with the use of valve opening of 0.020in as the basis of my duration measurements: in order to incorporate the mushroom effect into the duration readings.
I measured total valve opening duration as well; in order to compare total duration to the "effective flow" duration based on 0.020in valve opening.
In summary: I decided to take duration measurements using the starting point of duration from 0.020in of valve opening, the generally accepted point of commencement of "effective flow". After taking those measurements; and after observing the physical operation of the cam lobes/tappets at that 0.020in lift point, and beyond that point; I have concluded that using 0.020in valve lift as the duration reference is the wise course of action....on these SOHC cams.
UPDATE: I am in the process of organizing a followup gallery on camshafts. In it will be more camshafts, and the measurements of duration will be listed for all three methods:
...TOTAL duration
...duration at 0.020in lift
...duration at 0.050in lift
That will remove the confusion; and will standardize the comparisons completely.
Why so? Because the clearance ramps DO affect the lobe's operation.
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...valve event timing: opening and closing points at .020in lift; measured in crankshaft degrees
...valve overlap
...cam lobe center angle [hopefully]
...lobe separation angle [also hopefully]
...cam lobe base circle
Accuracy of measurements: within 2 degrees; within 0.002in
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I am satisfied that my accuracy in taking the measurements was tighter than "two and two". And that I could have been a bit of a smartass and made such claims. But I won't claim absolute accuracy; it is not necessary for my purposes. As long as I can be within 'two and two' consistently, the measurements are very useful for comparison purposes.
The other reason why I only claim "two and two" is this: I did not run 100 T cams or A cams through the measuring procedure so as to establish real and serious averages on all the dimensions. Perhaps some day when I have nothing better to do than run 100 camshafts through the procedure, I might.
Bottom line: I am satisfied that my readings are within "one and one"; but am not that much of a smartass.
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T cam intake valve results:
max valve lift: 0.389in
actual valve lift: 0.375in
valve duration: 218 degrees @ 0.020in valve lift
TOTAL duration: 254 degrees
valve event timing: opening of .020in at 0 degrees BTDC; closing to .020in at 38 degrees ABDC
T cam exhaust valve results:
max valve lift: 0.389in
actual valve lift: 0.375in
valve duration: 218 degrees @ 0.020in valve lift
TOTAL duration: 254 degrees
valve event timing: opening of .020in at 39 degrees BBDC; closing to .020in at 1 degree BTDC
Combined readings:
valve overlap: -1 degree
[based on the 0.020in valve lift numbers]
cam lobe center angle, intake: 109 degrees
cam lobe center angle, exhaust: 109 degrees
lobe separation angle: 109 degrees
cam lobe base circles: 1.417in
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A cam intake valve results:
max valve lift: 0.412in
actual valve lift: 0.398in
valve duration: 236 degrees @ 0.020in valve lift
TOTAL duration: 288 degrees
valve event timing: opening of .020in at 10 degrees BTDC; closing of .020in at 46 degrees ABDC
A cam exhaust valve results:
max valve lift: 0.412in
actual valve lift: 0.398in
valve duration: 236 degrees @ 0.020in valve lift
TOTAL duration: 288 degrees
valve event timing: opening of .020in at 48 degrees BBDC; closing of .020in at 8 degrees ATDC
Combined readings:
valve overlap: 18 degrees
[based on the 0.020in valve lift numbers]
cam lobe center angle, intake: 108 degrees
cam lobe center angle, exhaust: 110 degrees
lobe separation angle: 109 degrees
cam lobe base circles: 1.417in
