Intake valve lift at BDC
Moderator: Team
Re: Intake valve lift at BDC
Im assuming most here are likely not content with 100% VE or less. So why not look at things at and around the area where higher than 100% VE occurs.?
- Stan Weiss
- Vendor
- Posts: 4802
- Joined: Tue Feb 20, 2007 1:31 pm
- Location: Philadelphia, PA
- Contact:
Re: Intake valve lift at BDC
What I like to do is look at the intake port flow graphed as a function on the valve lift curve.
Stan
Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
-
- HotPass
- Posts: 3445
- Joined: Sat Feb 23, 2013 5:42 pm
- Location:
Re: Intake valve lift at BDC
This.
Focusing on the torque curve and horsepower will fall in line...
Here is a spare engine from a top MotoAmerica / FIA Superbike privateer team:
Being able to graph mass flow in EngMod4T has been most revealing to me.Stan Weiss wrote: ↑Tue Apr 28, 2020 1:55 pm What I like to do is look at the intake port flow graphed as a function on the valve lift curve.
Stan
-Bob
-
- Guru
- Posts: 1575
- Joined: Mon Apr 04, 2011 8:54 pm
- Location: central Florida
Re: Intake valve lift at BDC
Here's a hypothetical premise for discussion:
"On a fluid dynamics basis, the ideal intake valve lifts approaching BDC and on to IVC would produce optimum mixture velocities through the curtain area in support of the inertial ram process to maximize V.E. From max lift onward, some of these 'ideals' might well be much less than the mechanically-constrained current practice."
"On a fluid dynamics basis, the ideal intake valve lifts approaching BDC and on to IVC would produce optimum mixture velocities through the curtain area in support of the inertial ram process to maximize V.E. From max lift onward, some of these 'ideals' might well be much less than the mechanically-constrained current practice."
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
-
- Guru
- Posts: 1575
- Joined: Mon Apr 04, 2011 8:54 pm
- Location: central Florida
Re: Intake valve lift at BDC
Bill, i believe that i may have comprehended your Mechanical Engineer wording . Might you be thinking that the lift of the intake valve may well need to be a lesser amount at a given position in the cycle to maximize cylinder fill Mark H.
-
- Guru
- Posts: 6353
- Joined: Tue Jul 24, 2012 11:15 am
- Location: Roseville, Michigan (just north of Detroit)
- Contact:
Re: Intake valve lift at BDC
AND, then compare that to the piston position in the bore.Stan Weiss wrote: ↑Tue Apr 28, 2020 1:55 pm What I like to do is look at the intake port flow graphed as a function on the valve lift curve.
Stan
http://www.rmcompetition.com
Specialty engine building at its finest.
Specialty engine building at its finest.
Re: Intake valve lift at BDC
Exactly! (It sounds so simple when you put it like that... )swampbuggy wrote: ↑Wed Apr 29, 2020 7:06 am Bill, i believe that i may have comprehended your Mechanical Engineer wording . Might you be thinking that the lift of the intake valve may well need to be a lesser amount at a given position in the cycle to maximize cylinder fill Mark H.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: Intake valve lift at BDC
Well, RPM would definitely be a factor. Lift at BDC is going to be directly tied to IVC, which is directly tied to RPM. You can only shut the valve so fast. Too much lift at BDC would mean too late of IVC..too late of IVC within a given rpm or application can definitely hurt power...
-
- HotPass
- Posts: 3445
- Joined: Sat Feb 23, 2013 5:42 pm
- Location:
Re: Intake valve lift at BDC
My graph from an old thread. Simulated mass flow vs piston position vs valve lift profile.
You do not have the required permissions to view the files attached to this post.
-Bob
- Stan Weiss
- Vendor
- Posts: 4802
- Joined: Tue Feb 20, 2007 1:31 pm
- Location: Philadelphia, PA
- Contact:
Re: Intake valve lift at BDC
How does greater valve seat angles which reduces effective curtain area at lower lifts come into play?
I believe that this has been talked about before but can not find it.
Stan
I believe that this has been talked about before but can not find it.
Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
-
- Guru
- Posts: 9633
- Joined: Tue Nov 27, 2007 9:27 am
- Location: Chicago
- Contact:
Re: Intake valve lift at BDC
What if the piston position curve were replaced by a piston air demand curve?hoffman900 wrote: ↑Wed Apr 29, 2020 10:25 am My graph from an old thread. Simulated mass flow vs piston position vs valve lift profile.
3F6D2883-79F1-4815-A3C3-C728A991E951.jpeg
The inlet air mass flow curve shows twin peaks at near maximum piston speed. But at BDC
the piston air demand is minimal so that any continuing air mass flow must be a function of
air column momentum (actually, column pressure). This value would change with rpm while the
position (not amplitude) of piston air demand would remain constant.
If the valve curtain area is inadequate (relative to piston air demand) then the port velocity
will never reach its maximum capability. As Darren Morgan often stated: inlet flow is a
function of valve seat geometry.
-
- HotPass
- Posts: 3445
- Joined: Sat Feb 23, 2013 5:42 pm
- Location:
Re: Intake valve lift at BDC
I can work on that later. It should be noted that is mass flow a the valve seat. The port is more subdued of a curve and doesn't necessarily show as much negative mass flow at both ends of the lift curve.David Redszus wrote: ↑Wed Apr 29, 2020 12:16 pmWhat if the piston position curve were replaced by a piston air demand curve?hoffman900 wrote: ↑Wed Apr 29, 2020 10:25 am My graph from an old thread. Simulated mass flow vs piston position vs valve lift profile.
3F6D2883-79F1-4815-A3C3-C728A991E951.jpeg
The inlet air mass flow curve shows twin peaks at near maximum piston speed. But at BDC
the piston air demand is minimal so that any continuing air mass flow must be a function of
air column momentum (actually, column pressure). This value would change with rpm while the
position (not amplitude) of piston air demand would remain constant.
If the valve curtain area is inadequate (relative to piston air demand) then the port velocity
will never reach its maximum capability. As Darren Morgan often stated: inlet flow is a
function of valve seat geometry.
The lower the rpm, the more the curve follows the motion of piston demand, as piston speed increases it does what you see there, where the column pressure (momentum) and wave dynamics take over the filling process.
I believe the twin peaks near maximum piston speed is the sim picking up what would be the wave reflection by the very fast moving piston.
I hope this also illustrates that air does not "slam in the back of the valve" as coined by Superflow (I believe this was an imagined phenomenon and has been put into print so many times, it's become a "rule"). As MadBill said here probably a decade ago, if the air is slamming into the back of the valve, then it's probably closing the valve too soon
-Bob
- Stan Weiss
- Vendor
- Posts: 4802
- Joined: Tue Feb 20, 2007 1:31 pm
- Location: Philadelphia, PA
- Contact:
Re: Intake valve lift at BDC
If my intake valve closes @ lets say 80 ABDC. Then the piston has been compressing the air / fuel mixture for 80 degrees. How much above outside BP is the pressure on the back side of the valve to continue to have flow into the cylinder?
Stan
Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV