mattdel

whats the difference between Advertised duration and actual duration, why do they vary

FullAuto

Different companies measure difference from a different starting point. So the same cam could have a different measurement from brand to brand. That's why there is duration @ .050. Every manufacturer starts from the same point so there is a fair comparision.

tinman

Ther are some folk's that say that the duration @.050 don't mean much untill lift is over .600 but I think they are full of it.
There is NO SAE standard that I know of for measuring cam duration.
Use the .050 numbers and I think you'll be OK......

Ecstasy

well unless you got a stroker motor you really dont want a really high duration, because.

tinman

Ecstasy, wrong-o bud. With a longer stroke you can use both more lift and duration.
Within limits.
Where I think lots of peeps get into trouble is the cam grinders like to ,list everything for a small block Ford togather in the books and then the guy gets too much cam in a 5.0.
Same can be done with heads too, it's easy to get too much.
Heads, induction, compression, bore and stroke all have to be taken into account before any cam selection can be made......