What is Lobe Area

[csx7031]

... and what does it affect? I'm looking at a Cam Analyzer printout for the first time. All input welcome. Thanks, Chuck

[Walter R. Malik]

... and what does it affect? I'm looking at a Cam Analyzer printout for the first time. All input welcome. Thanks, Chuck

A lobe profile will present a curve like a bell shape ... lobe area is the area under that curve.

[David Redszus]

... and what does it affect? I'm looking at a Cam Analyzer printout for the first time. All input welcome. Thanks, Chuck

A cam lobe area is the summation of lift at every degree of rotation.
It is sometimes called "angle area."

It can be measured at the cam or at the valve. The later is preferred.

Using the Cam Analyzer, examine the acceleration curve; it is the most important curve of all.

[engineguyBill]

When camshaft events are plotted on a graph (valve lift per degree of crankshaft rotation) the area under the graph is referred to as the lobe area. Theoretically, the more area under the graph results on more air/fuel being passed through the engine and the higher the volumetric efficiency - BUT real world testing has proven that this is not necessarily true. When and how the valve is opened/closed are important considerations when designing cams for four cycle engines (actually any engine for that matter . . . . .)

[csx7031]

Thanks for all the responses. So lobe area reflects acceleration rates of the ramps, is that correct? Does a smaller number mean higher acceleration rates? Does the number indicate the ability of the cam to maintain valve train stability at high RPM? Sorry for all the perhaps stupid questions, I'm really trying to understand what is happening and why it is happening. Thanks, Chuck

[Walter R. Malik]

Thanks for all the responses. So lobe area reflects acceleration rates of the ramps, is that correct? Does a smaller number mean higher acceleration rates? Does the number indicate the ability of the cam to maintain valve train stability at high RPM? Sorry for all the perhaps stupid questions, I'm really trying to understand what is happening and why it is happening. Thanks, Chuck

A smaller lobe area number merely means the actual lobe is smaller and the actual area the valve is open is less.

This can be caused by the combination of any number of things; lift, duration, acceleration, velocity, etc.

[David Redszus]

Thanks for all the responses. So lobe area reflects acceleration rates of the ramps, is that correct? Does a smaller number mean higher acceleration rates? Does the number indicate the ability of the cam to maintain valve train stability at high RPM? Sorry for all the perhaps stupid questions, I'm really trying to understand what is happening and why it is happening. Thanks, Chuck

Lobe area (or angle area) does include the area contributed by the opening and closing ramps.
But lobe area has nothing to do with valve acceleration rates of the ramps or the rest of the cam.
The lobe area is only an approximation of the flow area provided by the cam and valve train.

As EngineguyBill correctly stated, lobe area is not an accurate predictor of performance. The reasons are several:
lobe area includes the ramps at IVO and IVC, both of which may be experiencing reversionary or negative flow. If so, negative values must be subtracted from the total lobe area.

Lobe area (angle area) measurements are static predictions. In an actual running engine, the valve does not perfectly follow the cam profile; the valve flutters and vibrates a lot, particularly at certain rpms.

While we start with a lift curve, either computed or measured, its real value is that it allows us to compute valve velocity, acceleration and higher derivatives. The valve velocity curve can be used to determine required tappet diameter and ramp characteristics. It can be used to identify a cam intended for solid lifters or hydraulic lifters.

The acceleration curve is used to determine the valve forces, positive and negative, which are needed to determine valve spring rates and forces required to control the valve motion.

Valve train stability is predicted by the shape and value of the higher derivative curves. Smooth, continuous, jerk curves are required to produce a stable valve motion.

If your cam supplier really likes you (and trusts you), he can provide an accurate cam lift curve, seat to seat. It would not include rocker and valve train effects but would be a very useful start by which to compare cams.

While these gymnastics reveal camshaft dynamic behavior, they still do not tell us which cam should be used in a specific engine for its intended mode of operation.

[csx7031]

David, Many thanks for taking the time to respond. I think I understand at some level now. Chuck