Let's Build a 416 with Cast Iron Heads and Manifolds

12many said

If the heads highest flow is at a certain lift and you only cam it with a lift in that range than how much time is it really open at that lift? Not much. I’ve always understood (I know I’ve read that here and over on Speed-Talk among other sources) that you want more lift (to a point) so the valve spends theoretically more time in that usable lift range as it reaches a higher lift where it’s not really open there very long anyway. Maybe the flow bench experts can clarify or expound on this?

Edit: yup, I lnew I’ve read about this elsewhere. (again, more lift “to a point”)

One example: lift vs. peak head flow - Don Terrill’s Speed-Talk

Click to expand...

Port flow and at what lift does it go flat is the determining factor for valve lift. Kind of wasting expensive heads that will flow high numbers up to 0.700" lift. Conversely using a cam that provides that lift with heads that peak at about 0.500"lift is pointless. If the heads peak at 0.500" valve lift, then a cam that provides a max lift of 0.530" will allow a few degrees more time at that flow rate. Considering that higher lift requires stronger springs to maintain valve control, and those springs create higher friction in the engine. A few thousandths will not create exponentially high loading.