Confusion on published cam specs

[Trackrash]

If you want to learn way more than necessary about cam design here it is.

Secrets Of Camshaft Power - Hot Rod Network

Here is what I was talking about when I mentioned the peak lift may not be at the center of the lobe.

[tirwin]

Well, you know I always want to know more than necessary. Thanks for posting!

So if symmetry cannot be assumed, is there any way of determing the amount of overlap?

[Trackrash]

I would think, in theory at least, that you could still compute the overlap with the opening and closing numbers. What would vary due to asymmetry of the lobe would be the volume or area under the curve, but not the number of degrees of overlap.

[tirwin]

I think you’re right.

By the way, the reason I’m asking all this is that I’m working on a way to visualize cam differences. First, I needed to make sure my calculations were correct and I didn’t have any egregious errors. Second, I think my initial concern has been validated. Discrepancies and inconsistent specs are going to make it a challenge. I’ll give it some more thought and keep working on it. When I have something I’ll publish it so people can comment.

For instance, I can make an assumption that there is lobe symmetry. It won’t be perfect but likely good enough.

But that also brings me back to the question that still hasn’t been answered. Are the differences in the two different sets of specs for what is supposedly the same cam important?

[Bill Verburg]

Originally Posted by tirwin

I...
But that also brings me back to the question that still hasn’t been answered. Are the differences in the two different sets of specs for what is supposedly the same cam important?

It was answered back is post #2
to reiterate
there are different ways to spec cams
seat to seat in degrees
at 1mm lift
at .05" lift

also the valve lash spec is needed

the simplest way to compare cams is to look at the overlap timing spec which eliminates all the other variables


here's a survey of most factory cams, the one # that summarizes the impact of the cams is the overlap timing #, the higher the racier, the lower the more street/ecological