Relationship of lift & duration for cam specs

[VegasEx'r]

I've got a fairly technical question about cams. I know what lift & duration #'s represent, but I also know that bigger isn't always better. How can you tell what kind of cam you have when you look at its' specs? I know that there is much more info about a cam, but as far as ATV cams go, about all you can get from the manufacturer is lift & duration @ .050. So for example, the HRC specs are:

lift (in/ex); duration @ .050 (in/ex)
.350 .339; 254 256

This cam creates more power in the mid to top range, and sacrifices some power in the bottom (so I'm told). There has got to be a way to know this by looking at these numbers. Can someone explain to me how?

Thanks

[Wheelie]

The duration is the biggest factor in the RPM range of a cam. More duration = upper rpm power-----less duration= low to mid range power/stump pulling low end torque.

[bama400ex]

good question. anybody know of any good websites about engine building and math in general? i cant seem to find any. and im not talking about a website about how to rebuild a 350 chevy, im talking about the good technical stuff. blue printing, porting, math, rod ratio's, cams. anybody?

You really need to know the lobe center angles and the ramp speeds of a cam to make a solid decision (good luck). However most ramp speeds and duration of wide open lift of an aftermarket cam will be substantially more than a stock cam even if duration at .50 is the same. Longer rods usually transulate into a longer dwell time at tdc and contribute to more time for flame front travel at tdc and thus greater initial torque on the piston's downstroke. These are general answers to general questions as I am not an engine builder nor have any scientific specs on the ultimate 400ex engine- it has yet to be built. :confused: