how much NET valve lift to employ ?

[RevTheory]

I have two programs that somehow compute max lift. One uses valve size and the other I'm guessing intake duration plus total engine combo I'm sure, but they can be as much as .050 off for the same combo (.650 on one and .600 on the other, respectively). I wonder what each one uses to come up with that "max lift" value

Perhaps that's one of those calculations that nobody really pays attention to. Beats me as I've never built an engine to those exact lift numbers and compared the two.

[David Redszus]

Dynamically, it allows for more lift area where you need it (which isn't necessarily peak).

Correct answer.
Peak air flow does not occur at max lift; it occurs somewhat earlier where lift is less. By increasing max lift, the curve is also raised at the max flow crank angle.

But, if valve curtain area (lift, valve size) is adequate, and port area is adequate (at the anticipated rpm), then excess max lift may not be necessary.

[zums]

Dynamically, it allows for more lift area where you need it (which isn't necessarily peak).

Correct answer.
Peak air flow does not occur at max lift; it occurs somewhat earlier where lift is less. By increasing max lift, the curve is also raised at the max flow crank angle.

But, if valve curtain area (lift, valve size) is adequate, and port area is adequate (at the anticipated rpm), then excess max lift may not be necessary.

Explain "adequate"
Tom

[cjperformance]

Dynamically, it allows for more lift area where you need it (which isn't necessarily peak).

Correct answer.
Peak air flow does not occur at max lift; it occurs somewhat earlier where lift is less. By increasing max lift, the curve is also raised at the max flow crank angle.

But, if valve curtain area (lift, valve size) is adequate, and port area is adequate (at the anticipated rpm), then excess max lift may not be necessary.

Explain "adequate"
Tom

Enough to do what you want it to do!

[zums]

Correct answer.
Peak air flow does not occur at max lift; it occurs somewhat earlier where lift is less. By increasing max lift, the curve is also raised at the max flow crank angle.

But, if valve curtain area (lift, valve size) is adequate, and port area is adequate (at the anticipated rpm), then excess max lift may not be necessary.

Explain "adequate"
Tom

Enough to do what you want it to do!

Really,? no kidding, and how do you use adequate in your engine building process
Tom

[cjperformance]

Explain "adequate"
Tom

Enough to do what you want it to do!

Really,? no kidding, and how do you use adequate in your engine building process
Tom

C'mon that didnt get a giggle!?
Adequate as in, enough airflow/csa to support the hp required, enough valve lift to access that airflow, as a loose start I will look at "lift where airflow is adequate X .88" to get a "quick and dirty" look at how much lift i need then asses wether that lift is practical(can i use more or do i have to use less) for the use going off of requirements like drag, endurance, lifter type , duration, intake type, exhaust system type, rpm range that will be used and of course the ever present constraint of budget.

[swampbuggy]

What David R. From Chicago said about Peak air flow being at less than full lift, now this sheds some light on the importance of how big the intake valve actually is, who agrees with this? Mark H.

[David Redszus]

Valve lift cannot normally be specified independent of duration. There are limits to valve acceleration which must be observed. If acceleration limits are observed, then increased lift must result in increased duration. That may be good or may not.

[gruntguru]

Similarly - if you need more lift away from the centreline (eg at point of max flow), you have to increase max lift or duration (or acceleration).