To determine lobe centerline, measure at 0.050 on either side of maximum lobe lift and tak
Measuring lobe lift is extremely simple. All you need is a valid indicator with an extension so you can reach the cam lobe through the lifter bore. The indicator should be in the same line that the lifter would follow in order for the readings to be accurate.
Spin the crankshaft until the dial indicator is on the cam lobe's base circle. That is the area on the back side of the lobe that provides zero lift. When you know the dial indicator is on the base circle, zero out your gauge. Now, spin the crank and keep an eye on the indicator. As the lobe moves underneath the end of the dial indicator, the needle will start moving. Watch until the needle stops and begins to move in the opposite direction. This is maximum lobe lift.
It is important to note that lobe lift is not the same thing as valve lift. If you are checking against your cam card, make sure you are looking at lobe lift numbers. To determine total valve lift, multiply your maximum lobe lift findings by your rocker ratio. For example, if total lobe lift is 0.420-inch and you are using 1.6:1 ratio rocker arms, your total valve lift should be 0.672-inch.
The lobe centerline is defined as where max valve lift occurs and is measured in terms of crankshaft degrees from piston TDC. Lobe centerline is often-but not always-the halfway point of that lobe's duration. When this happens, it is called an "asymmetrical lobe" and is usually reserved for ultra high-end race cams.
Begin with the dial indicator in place on the intake lobe for the number-one cylinder and rotate the crankshaft clockwise until you reach the valve's maximum lift. Zero out your dial indicator. Now rotate the crank counterclockwise until you have dropped at least 0.100 in valve lift. Spinning the crank clockwise again, turn the engine until the dial reads 0.050. The 0.050 is our target number, but we went beyond it and then came back because you always want to take your readings with the engine turning in the same direction it will be when running. Slack in the timing chain can throw your readings off if you take any measurements when spinning the engine backwards. If you have all eight pistons installed, the rings can make turning the engine over and hitting your marks difficult. If you accidentally go too far, back up and try again. Just do not take any readings directly after turning the crank counterclockwise.
The NASCAR Technical Institute's worksheet for determining lobe centerline. Courtesy of NT
Once you have the indicator on 0.050, take a reading from the degree wheel. Most degree wheels allow you to measure in degrees from TDC (the zero mark) in both directions. Count the degrees from TDC to your pointer along the shortest path. In other words, your reading should be less than 180 degrees. Once you have that measurement taken, rotate the engine clockwise past maximum valve lift until it has dropped 0.050 on the other side. Take your measurement from the degree wheel once again. And again, take the shortest path as you count up from the TDC mark to the pointer (it should be less than 180 degrees).
Your centerline is the average of those two numbers. For example, if your readings were 60 and 145.5 degrees, then your centerline would be 102.75. This means that the intake valve reaches max lift 102.75 degrees after the piston has reached TDC. Repeat the process again for the exhaust valve.
The process for measuring duration is similar to finding lobe centerline, except you measu
Once you are able to determine your lobe centerline, it is possible to influence your engine's power band by advancing or retarding the camshaft's position relative to the block. There are several different ways to change your cam timing, but all vary the relationship between the cam gear and the crank gear in some way.
Advancing the cam timing moves the valve opening and closing events earlier in the cycle. Since the relationship between the intake and exhaust lobes cannot be changed, advancing or retarding a cam affects both the intake and exhaust valve equally. Also, the most important thing advancing or retarding a camshaft affects for engine power is when it closes the intake valve. For example, if the camshaft is advanced, the intake valve closes sooner. This typically increases cranking compression on a high-duration race cam. The result is more torque and power in the lower rpm ranges. But as the rpms increase, the velocity of the air/fuel charge in the intake ports also increases dramatically and the early intake valve closing hurts power.