Hi-lift flow vs Mid-lift flow 2

[Rick360]

When porting a set of heads there are ways to enhance high, mid or low lift flow characteristics. I realize the ideal is to gain at all lifts but sometimes there is a tradeoff.
Which one would you trade for what other one? and why?

I profiled a cam which has .800" net lift thru its entire lift curve to see how long the valve was at what point, the piston velocity, and the flow at that lift. I then calculated theoretical flows throughout the intake stroke to see which lift points made the bigger difference. It seems that .700" and up had a bigger effect. Does this hold true on a dyno? Would gaining 10cfm at .7" - .8" be worth giving up 10 cfm at .5"-.6"?

Rick

 

[SMOKEY44211]

I have found the biggest single factor affecting low, mid and high lift flow is the valve seat angle. Shallow angles (15-30deg)tend to favor low lift flow. In some racing classes where the cam may be lift restricted there is some gain to optimizing low lift flow. Current trend in Pro stock drag class seems to favor steep (55deg) intake valve angles to take advantage of the high lift flow. Port shape and sizing seems to favor all lift ranges. If a port change enhances high lift flow low lift flow is better also.---------Phil

 

[Rick360]

There are things that can help at certain lift ranges on some types of heads. What I would like to know is which is more important. Is it the highest .100" that matters most given equal port sizes, as I have calculated?

Rick

 

[patprimmer]

I don't think it's that simple

It will depend a lot on cam profile, pressure gradient across the port to chamber interface and piston speed at the particular valve lift. This is I think a complex subject and variable from engine to engine.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SMOKEY44211]

If highest power is your primary consideration then I would have to say high lift flow is paramount. When the other factors of fuel economy, desire for broader torque curve, physical restrictions, rules restrictions enter into the equation then you are forced to look at both ends of the lift/flow curve. Every application has a different answer based on those variables.-----Phil

 

[MaxRaceSoftware]

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]

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]

(.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
Support Israel - Genesis 12:3

 

[CurtisBoggs]

Larry,

I have a simular problem, .. and have several questions for you, ..
but I'll start with a description of my project.

Round port, 3" long, 1.24" round at gasket tapering to 1.34" at the short turn or entry into the valve bowl.
The valve bowl is 1.40", throat under valve is 1.290" and the OD of the valve is 1.54"

spec cam has a max lift of .348" at the valve.

So, .. low lift flow is all I have to go after and the flow number that seems to transfer to the dyno & race track is .250" to .300"

I've been able to get 94 cfm @ 10" h2o at .350" lift.

So my questions, .. first your overall thoughts on the port size and their effects on the flow at .300" VS .200"

Second, .. I have been a "hands on" cylinder head guy for most of my life, ,,
and lack the math knowledge without the use of computers. Tips on getting the basics for a guy like me, . . . teach an old dog to be an engineer?

Curtis

Curtis Boggs
Racing Flow Development

http://www.raceflowdevelopment.com

 

[MaxRaceSoftware]

.226 Lift/Diameter Ratio = (.348 / 1.540)

so its below the .25 L/D Ratio Valve-to-Port transition point, that means the valve job and Bowl-Area is mostly controlling all the Flow characteristics.

don't make the Cross-sectional area larger than 1.490 sq.in
and probably smaller than 1.200 is too small unless you are turning this engine at very low RPMs ?

Valve-----Curtain(effective)
Lift------Area
.200------0.714 sq.inches
.300------1.071
.348------1.242
.400------1.428

94 cfm @10" = 157.3 cfm @ 28 inches

1.540 od = 1.863 area = 84.4 cfm/sq.inch ratio @ 28"

----HP per Cylinder (28")-----(600 Rpm/Sec Dyno Rate)----
.257 Flow Factor = 40.4 HP potential per Cylinder
.285 Flow Factor = 44.8 for very good SuperStock engines
.300 Flow Factor = 47.2 for 16:1 CR State-of-Art ProStock


1.290 / 1.540 = 83.8 % ..sort of small ...should be able to effectively use 87 to 90 PerCent at the throat or seat insert area
87+ % percent should work better ??


------Velocity in Feet per Second-----(.350" Lift & 28")
1.240 area at gasket = 312.6 fps
1.410 area at valve bowl = 267.7 fps
1.307 area at throat = 288.9 fps

312.6 fps is about the highest velocity you would want to see inside your Port at the smallest cross-sectional area when flow tested at 28 inches ...anything too much higher than that will be on the verge of loosing HP ..you sure won't be able to push it past 350 fps at 28 inches

at 10 inches = 209.3 fps is too high
at 28 inches = 350.3 fps is too high
at 36 inches = 397.2 fps is too high

even though you see Flow gains on the Bench it will begin not to correlate into real world HP past 350 fps port velocity at 28 inches or 209.3 fps @ 10 inches...in fact if you make the head flow more with a Sonic Choke problem..you'll just make the head go sooner into Sonic Choke on a live engine

at 350 fps at 28 inches you might only see a few HP loss, but as go go past that point...HP drops like a rock as Sonic Choke sets in earlier in the Lift Cycle

Example=> small Block Chevy engine 570 HP 165 cc port volume 1.940/1.500 valves 375 fps port velocity max @ 36 inches on FlowBench with 36 " Test Pressure

2 different pairs of the same exact casting number/valve sizes/port volumes/etc. ..even have identical flow numbers on intake and exhaust sides (just different port shapes)

1 pair has 458.6 fps port velocity at 36 inches
and looses over 75 HP at 7500 RPM compared to the other identical pair of heads that had 375 fps port velocity

if you add more max lift with a head like this, you just go into Sonic Choke earlier..thats why some engines don't respond to cam/valve lift increases.

if your engine doesn't like at least .37 Lift/Diameter Ratio then you have a severe Sonic Choke/Flow restriction problem

if rules allow , on the Intake side an engine should like .37 to .42+ L/D Ratio on max effort type engines

if port axis to valve axis is severe..heads might only respond up to .37-.39 L/D Ratio..as short turn radius gets better and port-to-valve axis gets better, then engine should respond towards .41-.42+ L/D Ratios on the Intake side

the Exhaust L/D Ratio is usually 95+ PerCent of the Intake side

in all out max-effort engine =

your valve sizes should ultimately determine cam's max lift

your desired engine operating RPM range should determine
overlap period and durations


Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[CurtisBoggs]

Larry,

A few questions, .. the curtain area at .300" how much will that flow?
what's the best possable?
also, .. I'm very bad at math, .. is there a spread sheet available to do the calc's, .. curtian area, .. etc.?

About the "sonic choke" these Velocities you referr to, .. how does that translate to the running engine, .. as the dynamic velocities must be much higher.

This is a restricted engine, .. stock cam, Webber 2bl. carb, .. 9.5:1 comp.
we turn them about 7000 max, .. peak HP tendes to be around 6200.

A more complex problem, and one you have made a refference to.

Just ran a track test a few weeks ago, .. ran a baseline, .. then swapped on my head, car went a second a lap faster on a 2.6 mi road course.
Huge gain, and the driver said he could feel the difference.

That engine got pulled and went to builder "A", ran back to back dyno on the two heads, .. showed less then 1/2 hp difference, .. and the TQ and HP curves where the same.

The faster head from the track test them came to a test in MD, .. rebuilt shortblock, .. and a back to back with my head and the customer's best head, .. less then 1/2 hp difference. The only difference I could find is the BSFC on my head was 2-3 points higher, .. with the same 1280 a/f setting.

But we know it's faster on the track, .. customer could feel the difference, .. and the lap time didn't lie, . I was at the test.

So, .. what's the deal????? If the car goes faster but we can't measure the difference on the dyno it has to be acceleration rate, .. but a second a lap? Now we tested at Watkins Glen, .. known as a HP track.

Your thoughts, .. is there a way to measure this.

With this combo this has been happining often, .. seeing no real gain over another ported head on the dyno but they run great on the track??????

Thanks,

Curtis



Curtis Boggs
Racing Flow Development

http://www.raceflowdevelopment.com

 

[MaxRaceSoftware]

A few questions, .. the curtain area at .300" how much will that flow?
what's the best possable?
also, .. I'm very bad at math, .. is there a spread sheet available to do the calc's, .. curtian area, .. etc.?
--------------------------------

theoretical flow at .300" lift should be = 93.4 cfm @ 10"

10 inches of Flow Test Pressure =>209.3 fps

209.343 fps = (10 ^ .5) * 66.2
where 10= Test Pressure & 66.2 = Units Constant , ^.5= SquareRoot


then CFM = FPS * Area * .41666667
so 93.4 CFM = 209.343 fps * 1.071 * .41666667

where 1.071 is the Effective Curtain Area @ .300" Lift
and i'm calculating all this stuff on a handheld calculator & posting from my Home Computer..all my Formulas/Equations/Software are on my Shop Computer so i maybe off a few thousandths at .300" Lift for your Effective Curtain Area... i already noticed a few math errors in my previous Post

------Velocity in Feet per Second-----(.350" Lift & 28")
1.240 area at gasket = 312.6 fps
1.410 area at valve bowl = 267.7 fps
1.307 area at throat = 288.9 fps

should read this instead
------Velocity in Feet per Second-----(.350" Lift & 28")
1.208 area at gasket = 312.5 fps
1.410 area at Short Turn = 267.8 fps
1.540 area at valve bowl = 245.1 fps
1.307 area at throat = 288.9 fps


<<<About the "sonic choke" these Velocities you referr to, .. how does that translate to the running engine, .. as the dynamic velocities must be much higher.<<<

10 inches of Flow Test Pressure =>209.3 fps

209.343 fps = (10 ^ .5) * 66.2
where 10= Test Pressure & 66.2 = Units Constant , ^.5= SquareRoot

you are Flow testing at 10 inches of Test Pressure , so if
you see 10 inches "or more" of Pitot Probe pressure, then
you are close to starting point where that 209.343 fps on the FlowBench will begin to correlate into Sonic Choke in live engine condition 600 to 700 fps (82.2 to 111.8 inches) Same thing at 28" or any test pressure...if your Pitot Probe pressure reading at the smallest cross-sectional area is equal to or greater than your test pressure the FlowBench will begin not to correlate to real HP


<<<The faster head from the track test them came to a test in MD, .. rebuilt shortblock, .. and a back to back with my head and the customer's best head, .. less then 1/2 hp difference. The only difference I could find is the BSFC on my head was 2-3 points higher, .. with the same 1280 a/f setting.
But we know it's faster on the track, .. customer could feel the difference, .. and the lap time didn't lie, . I was at the test.<<<<


take some Pitot Probe readings as you Flow Test your heads
use a 180 deg or "J" type Probe on the Intake side
you want to measure velocity fps...see what you come up with between the 2 Heads

Plenum volume or entire Induction volume can cause differences between Track and Dyno

the engine with higher BSFC's usually runs slower down the DragStrip compared to what Dyno might show

how much different is the Engine Rpm/Sec accel rate on the Road Course compared to on the Dyno ??

Dyno headers & Dyno exh lengths/mufflers -vs- in Car exhaust, can change how much HP engine makes in the Car

one Head might like the Dyno exhaust and make 200 HP
the other Head might not like the Dyno exh but still make 200 HP, but more in the Car with real headers/exh system

an onboard Data Recorder also linked to Strain Gauge setup on driveshaft yoke would reveal a lot of useful info .





Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[CurtisBoggs]

I didn't mean to hi-jack Rick's thread here, .. Rick are you OK with this?

Larry,

Thanks for the time you take to discuss this, ..

The FASTER head had 2-3 higher BSFC on the dyno at 1280 a/f.
I think the dyno headers are the same as what we used in the car, ..

I know port volume on the faster head is a few cc's larger, . . .

The kicker to this is, .. this has been happining with all the engine builders I supply. Dyno numbers don't look that different but the on-track performence is much better. Four different dynos, .. four different engine builders, .. same engine package.

Thanks for the math lesson on the curtain area & flow. I need some serious work on my math skills. ;-)
By your calc, .. I'm getting all that the curtain area will flow, .. around 93 cfm @ 10", .. My new flow bench being built will flow 900 cfm @ 36", .. I'm going to try some tests at 36" to see if a difference shows up.

Another thing to throw in the mix, .. and maybe the reason why the BSFC is up. With the limited cam we retard the stock cam to get the engine to run up high. I took the exhaust port and made it flow 100% of the intake at .050" up to .200", .. the idea was to help scavenge the cylinder and help the cam.

The real problem is I have one engine builder that seems to "challenge" me on this. If it doesn't run better on the dyno it "can't" be better on the track?

Thanks,

Curtis

Curtis Boggs
Racing Flow Development

http://www.raceflowdevelopment.com

 

[MaxRaceSoftware]

>> My new flow bench being built will flow 900 cfm @ 36", .. I'm going to try some tests at 36" to see if a difference shows up.<<

tryout 50" to 60" Test Pressure also and see if theres a difference ??


Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[GT6Steve]

Larry says "an onboard Data Recorder also linked to Strain Gauge setup on driveshaft yoke would reveal a lot of useful info".

Forgive me changing the subject but this sounds like an onboard dyno. Can you elaborate on the strain gage setup?

Steve

 

[MaxRaceSoftware]

>>the Exhaust L/D Ratio is usually 95+ PerCent of the Intake side<<

the above is wrong, it should have read =>

the Exhaust Valve Lift is usually 95+ PerCent of the Intake Side

================================================

Forgive me changing the subject but this sounds like an onboard dyno. Can you elaborate on the strain gage setup?
---Steve

http://www.land-and-sea.com/rotary-shaft-dyno/rotary-shaft-dyno.htm

Steve checkout the above Link ... there are more articles on this elsewhere .




Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[CurtisBoggs]

Larry,

Did some flow tests at higher pressures, .. didn't find anything significant. My exhaust port does flow better at low lifts though.

The only thing I haven't done is wet flow tests, .. .. so I'm guessing
that my valve job VS the other valve job has better wet flow.

Since you've seen identical engines on the dyno run different on the track, .. have you been able to trace it back to why???

Thanks,

Curtis

Curtis Boggs
Racing Flow Development

http://www.raceflowdevelopment.com

 

[CurtisBoggs]

seat angle?

any experience with a 30º or 35º seat angle, ..

do they live, .. how long etc. ????

Curtis


Curtis Boggs
Racing Flow Development

http://www.raceflowdevelopment.com

 

[MaxRaceSoftware]

Since you've seen identical engines on the dyno run different on the track, .. have you been able to trace it back to why???--Thanks,--Curtis
---------------------------------


So far on my SF-901 Dyno the Engines run what they should down the DragStrip,...but i've heard a few Stories like your's .


Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[MaxRaceSoftware]

seat angle?

any experience with a 30º or 35º seat angle, ..

do they live, .. how long etc. ????

Curtis
--------------------

Pontiac and Oldsmobile used 30 deg seat/valve angles on a few OEM engines...i use to convert some these 30 deg to 45 angles for ET Bracket racing but that was with .450" lift cams and upwards

a 1.540 valve w/max .348" Lift would probably like a 30 or 35 deg VJ might be better..thats where you can experiment



Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3