does excess lift hurt velocity???
09-23-2004, 03:40 AM
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http://www.eng-tips.com/viewthread.cfm?qid=92513
Here is a great website for engineers. Click the link and this is a thread on mid lift VS high lift flow #s and there importance. Under the SN MAXRACESOFTWARE...Larry Meaux has some very good input. He talks about the potential gains from increased valve lifts as well as maximun recomended valve lifts. Great thread! Guys a genious
Its a bit tough to follow in some spots since he spits it out so quick. Here is a small excerpt.....read the bold letter statement near the bottom of my quoted paragraph.
Here is a great website for engineers. Click the link and this is a thread on mid lift VS high lift flow #s and there importance. Under the SN MAXRACESOFTWARE...Larry Meaux has some very good input. He talks about the potential gains from increased valve lifts as well as maximun recomended valve lifts. Great thread! Guys a genious
Its a bit tough to follow in some spots since he spits it out so quick. Here is a small excerpt.....read the bold letter statement near the bottom of my quoted paragraph.
use .87 % PerCent times the "Theoretical Cam's Max Lift"
then make sure i have great FlowBench CFM numbers from that point to ( .25 * Int_Valve_Diameter )....along without sacrificing too much flow at any other points below that range.
the .87 % => accounts for Valve Lash Loss, valvetrain deflection losses, some intake manifold and carb CFM loss,
and accounts for where the cam's "lift dwell time" would be most effective if you looked at Valve Lift / Piston Velocity / CFM demand
a .800" Lift cam - .025" Lash = .775"
.775" - another .025 to .030" valvetrain deflection loss
= .750" or so
.750" = valve lift is only at .750" a few degrees
.800" Lift times .87 % = .696" rounded off to .700" lift
cam will be at .700" lift to .500" lift when piston velocity is at maximum till cylinder volume is at maximum
its very important to have great Cyl Head Flow from
.25 * Int VD to between .37 to .41 times Int VD
Curtain_Area = Valve_Area when Valve Lift is .25 times Valve_Diameter
you still want Low-Lift flow to take maximum advantage of Inertia/Ram effects at Intake Valve closing point
and Intake Valve opening point...
but you want the Intake valve to act like a one-way valve
=> letting air flow into cylinder, but not letting air escape back out the cylinder
50,55,58 degree seat angles will help make intake valve seem like one-way valve...along with using a number of distinct valve seat angles ..instead of using a radius valve job on Intake side
on a few engine Dyno tests i did => Radius -vs- Angle
Intake valve jobs ....the "series of Angles" valve job on Intake side made Torque sooner in RPM curve and wider Torque Curve ..than the Radius Intake valve job...but both made close to same Peak HP
on older style cyl heads that have abrupt short turns
the Max_Useable_Valve_Lift = .37 * Intake_Valve_Diameter
on ProStock Technology;
the Max_Useable_Valve_Lift = .39 * Intake_Valve_Diameter
to
the Max_Useable_Valve_Lift = .41 * Intake_Valve_Diameter
anything greater seems to loose too much curtain area velocity without gaining enough CFM flow
.42 * Intake_Valve_Diameter would be the most Lift possible that would make Power
your Intake and Exhaust valve sizes should determine your Camshaft's max useable Lift in all out Race Engines !
to see if greater Intake Valve Lift would help ??
then just multiply ;
HP Potential Gain = .257 * CFM@28" * Number_of_Cylinders
.257
.285
.310 Factors
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
then make sure i have great FlowBench CFM numbers from that point to ( .25 * Int_Valve_Diameter )....along without sacrificing too much flow at any other points below that range.
the .87 % => accounts for Valve Lash Loss, valvetrain deflection losses, some intake manifold and carb CFM loss,
and accounts for where the cam's "lift dwell time" would be most effective if you looked at Valve Lift / Piston Velocity / CFM demand
a .800" Lift cam - .025" Lash = .775"
.775" - another .025 to .030" valvetrain deflection loss
= .750" or so
.750" = valve lift is only at .750" a few degrees
.800" Lift times .87 % = .696" rounded off to .700" lift
cam will be at .700" lift to .500" lift when piston velocity is at maximum till cylinder volume is at maximum
its very important to have great Cyl Head Flow from
.25 * Int VD to between .37 to .41 times Int VD
Curtain_Area = Valve_Area when Valve Lift is .25 times Valve_Diameter
you still want Low-Lift flow to take maximum advantage of Inertia/Ram effects at Intake Valve closing point
and Intake Valve opening point...
but you want the Intake valve to act like a one-way valve
=> letting air flow into cylinder, but not letting air escape back out the cylinder
50,55,58 degree seat angles will help make intake valve seem like one-way valve...along with using a number of distinct valve seat angles ..instead of using a radius valve job on Intake side
on a few engine Dyno tests i did => Radius -vs- Angle
Intake valve jobs ....the "series of Angles" valve job on Intake side made Torque sooner in RPM curve and wider Torque Curve ..than the Radius Intake valve job...but both made close to same Peak HP
on older style cyl heads that have abrupt short turns
the Max_Useable_Valve_Lift = .37 * Intake_Valve_Diameter
on ProStock Technology;
the Max_Useable_Valve_Lift = .39 * Intake_Valve_Diameter
to
the Max_Useable_Valve_Lift = .41 * Intake_Valve_Diameter
anything greater seems to loose too much curtain area velocity without gaining enough CFM flow
.42 * Intake_Valve_Diameter would be the most Lift possible that would make Power
your Intake and Exhaust valve sizes should determine your Camshaft's max useable Lift in all out Race Engines !
to see if greater Intake Valve Lift would help ??
then just multiply ;
HP Potential Gain = .257 * CFM@28" * Number_of_Cylinders
.257
.285
.310 Factors
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
Last edited by 383LQ4SS; 09-23-2004 at 03:50 AM.
