how much NET valve lift to employ ?

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RevTheory
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Re: how much NET valve lift to employ ?

Post by RevTheory » Tue Jul 17, 2018 10:31 am

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 :-k

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.

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Re: how much NET valve lift to employ ?

Post by David Redszus » Tue Jul 17, 2018 11:58 am

hoffman900 wrote:
Mon Jul 16, 2018 8:23 pm
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.

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Re: how much NET valve lift to employ ?

Post by zums » Tue Jul 17, 2018 8:00 pm

David Redszus wrote:
Tue Jul 17, 2018 11:58 am
hoffman900 wrote:
Mon Jul 16, 2018 8:23 pm
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

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Re: how much NET valve lift to employ ?

Post by cjperformance » Tue Jul 17, 2018 8:02 pm

zums wrote:
Tue Jul 17, 2018 8:00 pm
David Redszus wrote:
Tue Jul 17, 2018 11:58 am
hoffman900 wrote:
Mon Jul 16, 2018 8:23 pm
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!
Craig.

zums
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Re: how much NET valve lift to employ ?

Post by zums » Tue Jul 17, 2018 8:05 pm

cjperformance wrote:
Tue Jul 17, 2018 8:02 pm
zums wrote:
Tue Jul 17, 2018 8:00 pm
David Redszus wrote:
Tue Jul 17, 2018 11:58 am


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

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Re: how much NET valve lift to employ ?

Post by cjperformance » Tue Jul 17, 2018 8:25 pm

zums wrote:
Tue Jul 17, 2018 8:05 pm
cjperformance wrote:
Tue Jul 17, 2018 8:02 pm
zums wrote:
Tue Jul 17, 2018 8:00 pm


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!? :lol:
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.
Craig.

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Re: how much NET valve lift to employ ?

Post by swampbuggy » Thu Jul 19, 2018 11:29 am

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.

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Re: how much NET valve lift to employ ?

Post by David Redszus » Thu Jul 19, 2018 12:08 pm

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.

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Re: how much NET valve lift to employ ?

Post by gruntguru » Thu Jul 19, 2018 7:57 pm

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).

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