Mathematically speaking, it's dead-nuts accurate, at least when you're using .050 numbers. Those are the only things you need to calcluate the opening and closing points. If you have access to the cam card for your cam and you compare the numbers from it to what the cam calculator spits out they will be the same every time. All you're doing is reverse-calculating the numbers.

There is definitely weirdness when trying to compare Advertised lift numbers and .050 numbers, however. I'll jsut let you know that all the major cam companies numbers (including GM cams) will make a lot more sense to you if you use the .050 numbers.

If you use the Advertised lift numbers the words "relative" and "arbitrary" are being kind. I would even add "damned near random." Not only is the Advertised lift point arbitrarily chosen and different between different companies but it can even be different for different cams from the same company. Couple that with the fact that all modern cam designs lift the valve faster than they set it down and it makes it very tough to ever use Advertised durations for anything meaningful. There's good reason why .050 numbers are a much more widely accepted and better way to compare different cams.

 

Link worked for me.

 

Got the link to work today...don't know why it wouldn't work yesterday??

Off topic question, I don't understand this from the article:
Looking a bit further at the timing points, the first one we see on the diagram is the exhaust opening point. We have all noticed the different sounds of performance cams, with the distinct lopes or rough idle. This occurs when the exhaust valve opens earlier and lets the sound of combustion go out into the exhaust pipes. It may actually still be burning a little when it passes out of the engine, so this can be a very pronounced sound.

I thought idle quality had to do with overlap, not exhaust opening. I started a thread a few weeks ago about this exact topic and thought I had it understood.

 

The amount of lope and idle vacuum comes from the overlap, some extra sounds can come from too early of a exhaust valve opening.

Bret