Camshaft Terminology

[metalbeast]

Lift, duration, LSA...you hear Gear heads all over the world spouting off these camshaft terms. Just what do they mean? I will attempt to give definitions for the most common camshaft terminology.

Lift:

Lift can be divided into 2 categories Lobe Lift and Valve lift

Lobe Lift-If you were to cut a cam in to sections, then view those sections from then end you would notice that there are number of lobes (for a traditional OHV engine, 1 lobe for each intake and exhaust valve). These lobes resemble an egg when viewed from the end. The lobe lift is the amount that the lobe raises in radius above the base circle of the lobe.

Valve Lift-Generally speaking, valve lift is the distance that the cam lobe "lifts" the valve off of its valve seat. Maximum valve lift is calculated by multiplying the lobe lift by the rocker arm ratio. For example, if you know your lobe lift is 0.328 inches and you are using a rocker arm with a lift ratio of 1.6/1, then your maximum theoretical lift is 1.6x0.328 inches = 0.525 inches valve lift.

Duration:

If you take a look at your cam lobe again, you will notice that the profile of the lobe gradually slopes up then slopes back down to the base of the lobe. The number of degrees that the crankshaft turns in going from a given point on one side of the cam lobe to the corresponding point on the other side of the cam lobe is the duration of the cam lobe. Duration determines how long a particular valve remains in the open position. Duration is commonly measured in one of two ways:

Advertised Duration-This is the duration measured at 0.006 inches of lobe lift. In other words, once the lobe lifts the lifter 0.006 inches, the crankshaft degrees are measured until the point on the other side of the lobe where the lifter is 0.006 inches from the base circle.

Duration at 0.05 inches-As the name explicitly states, this the the duration measured from 0.05 inches lobe lift side to side. This is the standard used by engine builders to compare the duration of cams of different manufacturers.

Single & Dual Pattern Cams:

Single pattern cams are cams that have identical intake and exhaust profiles. In other words the lift and duration of both the intake and the exhaust is the same. Example: a cam with 220/220 duration, 0.500/0.500 lift is a single pattern cam.

Dual pattern cams have different intake and exhaust profiles. Therefore, the duration and the lift will be different for the intake and exhaust. Example: a cam with 233/236 duration, 0.550/0.576 lift is a dual pattern cam.

Centerlines:

The centerline for an intake or exhaust lobe is the midpoint in the duration of that lobe. Intake centerline is expressed in the number of crankshaft degrees after top dead center (ATDC). Exhaust duration is measured in the number of crankshaft degrees before top dead center (BTDC). The intake centerline of the number 1 cylinder is used to measure the position of the cam in relation to the engine.

LSA:

LSA is an acronym for Lobe Separation Angle. LSA is the number of camshaft degrees between the intake and the exhaust centerlines. LSA determines in large part, how much overlap you have between your intake and exhaust valves.

Overlap:

Overlap is the angle in crankshaft degrees at which both the intake and the exhaust valves are open. Overlap is a very important for engines that operate in the high RPM range. At high engine speeds, overlap uses the spent exhaust leaving the cylinder to pull in fresh fuel/air from the intake valve.

Well, those are the basics of camshaft terminology. Hopefully they will help you understand that funny looking bumpy stick they call a cam

[AAron]

good stuff.

this will help the newer guys figure out what we are talking about, and help them get on to the more involved info on cams

[jaberwaki]

ramp rate:
the percentage of angle grade that the lobe goes from .05 to peak lift, also described as how agressive you cams lobes are. the faster your lobe reaches your peak lift, the more agresive your cam lobes are.

Lobe events: Although most lobes have a basic egg shape to them, that does not mean that they are all PERFECT eggs, in fact a few dont look much like that at all. the reason for this is something called lobe events, an event is a change in one or all of the numbers in the cam at any given point in the cam. IE...

lets say a lobe starts at a 30% grade from .05 lift. but at .300 lift it gets much more agressive and goes to a 50% grade till it reaches your peak lift, and the return grade goes back to 30%.

these numbers are ficticious, only an example, but a good cam grinder can have a cam that advertises the EXACT same duration, lift, and LSA.... and still put out 10-20 more hp across the entire powerband. the reason is , the cam lobe events are MATCHED to the flow characteristics of your heads.



(just thought i would throw these in to show there is more to it then just advertised numbers ) feel free to copy and paist it into your write up and delete my part ;D

[metalbeast]

jaberwaki said:

ramp rate:
the percentage of angle grade that the lobe goes from .05 to peak lift, also described as how agressive you cams lobes are. the faster your lobe reaches your peak lift, the more agresive your cam lobes are.

Lobe events: Although most lobes have a basic egg shape to them, that does not mean that they are all PERFECT eggs, in fact a few dont look much like that at all. the reason for this is something called lobe events, an event is a change in one or all of the numbers in the cam at any given point in the cam. IE...

lets say a lobe starts at a 30% grade from .05 lift. but at .300 lift it gets much more agressive and goes to a 50% grade till it reaches your peak lift, and the return grade goes back to 30%.

these numbers are ficticious, only an example, but a good cam grinder can have a cam that advertises the EXACT same duration, lift, and LSA.... and still put out 10-20 more hp across the entire powerband. the reason is , the cam lobe events are MATCHED to the flow characteristics of your heads.



(just thought i would throw these in to show there is more to it then just advertised numbers ) feel free to copy and paist it into your write up and delete my part ;D

Excellent Jaber! I tried to write down all I could last night but I was pretty tired and I knew I would leave some stuff out (took me an hour to get down all the stuff in my head into something understandable in the thread). Everyone, cams are pretty complex items when you think about it so, if anyone else wants to add to the thread please feel free!!

[1bad2k2ta]

jaberwaki said:

ramp rate:
the percentage of angle grade that the lobe goes from .05 to peak lift, also described as how agressive you cams lobes are. the faster your lobe reaches your peak lift, the more agresive your cam lobes are.

Lobe events: Although most lobes have a basic egg shape to them, that does not mean that they are all PERFECT eggs, in fact a few dont look much like that at all. the reason for this is something called lobe events, an event is a change in one or all of the numbers in the cam at any given point in the cam. IE...

lets say a lobe starts at a 30% grade from .05 lift. but at .300 lift it gets much more agressive and goes to a 50% grade till it reaches your peak lift, and the return grade goes back to 30%.

these numbers are ficticious, only an example, but a good cam grinder can have a cam that advertises the EXACT same duration, lift, and LSA.... and still put out 10-20 more hp across the entire powerband. the reason is , the cam lobe events are MATCHED to the flow characteristics of your heads.



(just thought i would throw these in to show there is more to it then just advertised numbers ) feel free to copy and paist it into your write up and delete my part ;D

Good info. I would only add that more aggressive lobes are harder on the entire valve train, especially the lifters. The valves opening and closing will be accelerated and float can become a problem. Then you need stiffer springs which can cause the valve to hammer the valve seats. In a nutshell, you can make more power, but you will wear parts out faster. Just something to be aware of when you are planning your build. Sometimes you have to sacrifice some power for longevity, or conversely, some longevity for more power.

[jaberwaki]

1bad2k2ta said:

jaberwaki said:

ramp rate:
the percentage of angle grade that the lobe goes from .05 to peak lift, also described as how agressive you cams lobes are. the faster your lobe reaches your peak lift, the more agresive your cam lobes are.

Lobe events: Although most lobes have a basic egg shape to them, that does not mean that they are all PERFECT eggs, in fact a few dont look much like that at all. the reason for this is something called lobe events, an event is a change in one or all of the numbers in the cam at any given point in the cam. IE...

lets say a lobe starts at a 30% grade from .05 lift. but at .300 lift it gets much more agressive and goes to a 50% grade till it reaches your peak lift, and the return grade goes back to 30%.

these numbers are ficticious, only an example, but a good cam grinder can have a cam that advertises the EXACT same duration, lift, and LSA.... and still put out 10-20 more hp across the entire powerband. the reason is , the cam lobe events are MATCHED to the flow characteristics of your heads.



(just thought i would throw these in to show there is more to it then just advertised numbers ) feel free to copy and paist it into your write up and delete my part ;D

Good info. I would only add that more aggressive lobes are harder on the entire valve train, especially the lifters. The valves opening and closing will be accelerated and float can become a problem. Then you need stiffer springs which can cause the valve to hammer the valve seats. In a nutshell, you can make more power, but you will wear parts out faster. Just something to be aware of when you are planning your build. Sometimes you have to sacrifice some power for longevity, or conversely, some longevity for more power.

good point, it is exactly for that reason that when i am choosing a cam grind i want the "foward of peak" events to be very agressive, but on the after peak side(the way down) i want it to give a slightly more gentle slope.
this way you get as much opening time as you can(given the duration) and run the stronger spring, but it wont be as hard on your valve seats....