I would say that when picking a cam DURATION, the focus needs to be based more on the stroke than the overall cubic inches.

You can have a 5 inch bore, or a 4 inch bore. They both travel the same distance down the bore and spend the same time doing so in degrees of crank rotation, (no?) so I would say that generally they would both need roughly the same duration as one another and that the larger bore for example would need not necessarily more duration, but more of an opening to breathe through (larger cylinder head port and maybe higher valve lift) than the smaller bore, but not necessarily duration. A larger cylinder bore (larger cubic inches) isnt going to benefit from hanging the valve open any longer than the smaller bore.

Now take (again as an example) a 4 inch stroke and a 5 inch stroke.
The 5 inch stroke is going to have a piston travelling down the cylinder on the intake stroke (for example) for a longer length of time empasized in degrees of crank rotation than the 4 inch stroke. So by that virtue, you are going to want to open the valve for a longer time in crank degrees of rotation on the 5 inch stroke than the 4 inch stroke as the 5 inch stroke is spending more time creating a depression in the intake port, or breathing in.

So I would say that when picking a duration for a cam. It is really more reliant for the most part on what the stroke is than the actual cubic inches.

I briefly skimmed through the thread and correct me if I am wrong, but I didnt see any mention of stroke...but this is why an engine that has a longer stroke (408 over a 360) needs more duration, and also explains why the 360 with too much duration becomes a dog.

Think about that for a second....the 360 with 270 @.050 lobe isnt able to make the vac that the 408 would because the valves are open too long and a lot of that fuel isnt being retained in the cylinder to be burned, or even exhausted.

And this is why the 360 will have the higher powerband, and the same cam in the 408 will have a few hundred less rpm. Because of the stroke. Not really because of the cubic inches.

If I had a 360 and 408, (one larger than the other only because of bore size and not stroke for example) I would only want a larger port feeding the larger bore, and maybe more valve lift to help ensure that since the larger bore will indeed breathe in more air than the 360, but it's still spending the same amount of time doing so as the 360.

With a longer stroke, there is more time spent in degrees of crank rotation breathing in and that is where duration comes into play.

Not really.

More mistakes than content = too much work.

There are surly some mistakes but...If you read into the content, I think some of it is just the wording is wrong.... just simple stuff like time & speed. Even though its not technically correct, if you think about some of the opinions they have merit or express another way to look at things, most of the greatest achievements on this planet stemmed from mistakes. I understand why you don't post the long version anymore.... but bother to comment.... Vic, this was not to you.