Importance of mid-lift flow numbers
10-05-2004, 05:04 PM
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Importance of mid-lift flow numbers I have never started a thread so here I go. At 6000 rpm the engine sees max lift of the average street cam for .00003 of a second, but at the same rpm the engine sees mid lift twice so from the time the ramp passes mid lift to the time it ramps back down to mid lift takes .00388 of a second. Kind of puts things in perspective. CAN YOU BREATH THAT FAST?!
10-05-2004, 08:48 PM
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No I can"t but you"re motor can.Low to midlift flow is important because the air needs to start moving as soon as the valve first sstarts to open,also like you said the valves see the low to midlift numbers twice,going up and going down.Pretty cool! 
10-05-2004, 09:29 PM
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I check out a book at my local library on cams, I was looking for a cam and decide I needed to know more. Unbelievable complex, you better have a PHD math. I had on chance of understanding it. But one thing I did pick up, is how important low and mid flow numbers are, ramp angles.
10-05-2004, 10:25 PM
#7
I think he used:
(Duration @ a given lift)/(RPM*360*60)=time
You can get duration at a given lift off the cam card, 360 is for number of degrees in a revolution, 60 is to convert minutes to seconds. Converting to time doesn't really matter, you can just as easily compare duration in degrees at mid lift to max lift.
(Duration @ a given lift)/(RPM*360*60)=time
You can get duration at a given lift off the cam card, 360 is for number of degrees in a revolution, 60 is to convert minutes to seconds. Converting to time doesn't really matter, you can just as easily compare duration in degrees at mid lift to max lift.
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10-05-2004, 10:40 PM
#11
Originally Posted by KingCrapBox
I'm bored, so I'll throw this out. What is happening in your motor when the valve is only at .100" and .200" of lift?
10-05-2004, 11:07 PM
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I posted this in another thread. Its an enginerring message board with all types of info. One of the "gurus" on the automotive section is Larry Meaux. he has a close working relationship with Alan futral if Im not mistaken. the guy is a genious. Anyways...the link is a question on whats more important between midlift and high lift flow #s. LArry gives some good info here with very specific criteria. A little hard to follow because of the way he writes...but its all in there.
http://www.eng-tips.com/viewthread.cfm?qid=92513
Here is a little bit from ONE of his posts. he goes by MacRaceSoftware
http://www.eng-tips.com/viewthread.cfm?qid=92513
Here is a little bit from ONE of his posts. he goes by MacRaceSoftware
MaxRaceSoftware (Automotive) Apr 16, 2004
Rick360,
i 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
LJW (Industrial) Apr 19, 2004
What a great thread!
What is the best strategy for dealing with very low lift/diameter ratios (.428 total lift/1.570 Intake Valve diameter)? Are tricks to limit reversion helpful in engines that do not have a lot of overlap?
Larry Wiechman
MaxRaceSoftware (Automotive) Apr 20, 2004
(.428 total lift/1.570 Intake Valve diameter)
============================================
equals = .2726 Lift/Diameter Ratio
its above the .25 L/D Ratio ...so might watchout for effects of BackCut angle on the intake valve -VS- no BackCut angle on intake valve ....just depends on how you port the bowl-area , short-turn, and valve job.
a 1.570 Intake Valve , using a safe .87 Factor times OD
will give you 1.837 sq. inches of cross-sectional area
that you shouldn't exceed if you want good port velocity
Cross-sectional area = 1.570 * .87 * 3.1416 * .428
if you had no overlap period...the engine would still respond to low-lift flow and valve job specs
because of Inertia Ram/Wave tuning effects at intake valve closing point
you could use .87 , .89, .90, .91 to (.92 as absolute max)
Factor ....this Factor accounts for the fact that the actual diameter at seat insert is much less than the valve's OD because of seat angle widths and number of seat angles, and transition into bowl and short-turn.
same way with effective valve area calculation
you have to also account for the valve stem dia.
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Rick360,
i 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
LJW (Industrial) Apr 19, 2004
What a great thread!
What is the best strategy for dealing with very low lift/diameter ratios (.428 total lift/1.570 Intake Valve diameter)? Are tricks to limit reversion helpful in engines that do not have a lot of overlap?
Larry Wiechman
MaxRaceSoftware (Automotive) Apr 20, 2004
(.428 total lift/1.570 Intake Valve diameter)
============================================
equals = .2726 Lift/Diameter Ratio
its above the .25 L/D Ratio ...so might watchout for effects of BackCut angle on the intake valve -VS- no BackCut angle on intake valve ....just depends on how you port the bowl-area , short-turn, and valve job.
a 1.570 Intake Valve , using a safe .87 Factor times OD
will give you 1.837 sq. inches of cross-sectional area
that you shouldn't exceed if you want good port velocity
Cross-sectional area = 1.570 * .87 * 3.1416 * .428
if you had no overlap period...the engine would still respond to low-lift flow and valve job specs
because of Inertia Ram/Wave tuning effects at intake valve closing point
you could use .87 , .89, .90, .91 to (.92 as absolute max)
Factor ....this Factor accounts for the fact that the actual diameter at seat insert is much less than the valve's OD because of seat angle widths and number of seat angles, and transition into bowl and short-turn.
same way with effective valve area calculation
you have to also account for the valve stem dia.
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
10-07-2004, 09:30 AM
#13
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Welcome to the board.
I can't see the issue
. I don't think it is possible to have better high lift flow without better low lift flow into the bargain. Air flows to the maximum allowed in the system.
Go for the highest flowing heads you can find and they will also give the best low lift flow numbers.
And Yes, as the guys are already pointing out, the flow either side of peak lift is the most important.
Tom.
I can't see the issue
. I don't think it is possible to have better high lift flow without better low lift flow into the bargain. Air flows to the maximum allowed in the system.Go for the highest flowing heads you can find and they will also give the best low lift flow numbers.
And Yes, as the guys are already pointing out, the flow either side of peak lift is the most important.
Tom.
10-07-2004, 07:25 PM
#14
The reason why mid-lift flow is so critical on the LSX motor is that your piston is at maximum speed on the down stroke when the valve is opened between .300-.400" lift. Once the intake valve gets near and past .500" lift, the piston is starting to slow down as it approaches BDC. Put another way, there is more piston suction when the intake valves are at .300-.400" lift than there is when the valve is open more than .500" lift. Killer mid lift makes killer horsepower.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
10-07-2004, 07:31 PM
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Damn Al.... I understand this stuff pretty good, but I got lost like a little kid in the woods reading what you quoted... LOL (note to self, must slow down on the beer 
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10-07-2004, 07:45 PM
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Tommy some ls1 heads that flow say 300 cfm at .600 do have lower cfm numbers at say .300 or .400 compared to other heads.A good way to compare cfm is .100+.200+.300+.400+.500+.600+.500+.400+.300+.200+ .100,take the flow numbers from these lift numbers and add them together,you can divide by 11(these lift numbers added together) if you want just for comparison sake.Its more of a real life way the flow is every cycle,either intake or exhaust.
10-08-2004, 08:33 AM
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Hi Fastone,
My point with the flow thing was that I just can't understand a physical reason why a runner that flows well at .6 lift wouldn't flow well at .3 I get the reverse, obviously. 
My goals for the cam are getting wilder and wilder. I'm really tempted to go a bit crazy and see just how far I can go. I'm getting hold of a two piece T/C cover so I'll be able to swap out cams easily (mid-engined advantage). Also had some info from HSV1 (an Aussie) telling me that once you have a TB on each port the improvement at idle and in drive-ability is incredible. Predator posted a sound clip of a 242/242/106 and it idled like a dream. So that's the way I'm going.
A big thanks to you, Predator and Granny for helping me in understanding extreme cams a bit better the relevence of the LSA.
My point with the flow thing was that I just can't understand a physical reason why a runner that flows well at .6 lift wouldn't flow well at .3
I get the reverse, obviously. My goals for the cam are getting wilder and wilder. I'm really tempted to go a bit crazy and see just how far I can go. I'm getting hold of a two piece T/C cover so I'll be able to swap out cams easily (mid-engined advantage). Also had some info from HSV1 (an Aussie) telling me that once you have a TB on each port the improvement at idle and in drive-ability is incredible. Predator posted a sound clip of a 242/242/106 and it idled like a dream. So that's the way I'm going.
A big thanks to you, Predator and Granny for helping me in understanding extreme cams a bit better the relevence of the LSA.
10-08-2004, 10:16 AM
#20
Tommy, the mid-lift and high-lift thing is much like a see-saw. If you favor one too much, you hurt the other. You can set up the valve job with a steeper bottom cut, open up the venturi, and lay the short side radius back for killer high-lift numbers, but the mid-lift flow will suffer. Mid-lift likes a fatter short side radius, a shallower bottom cut, AND and smaller venturi to flow well. So, basically, the valve job, short side radius, and venturi size is specific for either mid or high lift.
The trick that all head porters try to do is find a happy place where mid and high lifts perform well. These days, whre people are running so much lift, up to .650" on the street, finding a combination of all those things so that the head has good flow everywhere in the curve is tougher.
The trick that all head porters try to do is find a happy place where mid and high lifts perform well. These days, whre people are running so much lift, up to .650" on the street, finding a combination of all those things so that the head has good flow everywhere in the curve is tougher.