Area under the curve.

[V Remian]

Does any one here use ''area under the curve" to evaluate ports or spec cams for flow characteristics?

[SStrokerAce]

In port flow or power numbers?

[V Remian]

I am talking about flow #s at each increment and calculating area.

[highVE]

any time i'm putting a new combination together, i have a cam ground based on my induction systime potential, and the rpm i intend on turning w/the motor. i'm sure you know this. but i think it's very important

[SStrokerAce]

Yeah evaluating the port flow at all lifts is important... some area's gains make more of a impact on power than others, usually around the top end since the valve spends most of it's time up there and that's where the highest port velocities are seen.

I don't think that you limit the cam because of the flow curve... say flow stops increasing after .500" lift, that doesn't mean that you limit the cam to that. Hopefully your port doesn't stall above that point and drop off in flow as well, but even if the flow is still increasing higher than you lift the valve it's ok as well... you give the motor what it needs and what the rules ask for.

Bret

[gas]

Yeah evaluating the port flow at all lifts is important... some area's gains make more of a impact on power than others...

I can agree with that!

.... usually around the top end since the valve spends most of it's time up there and that's where the highest port velocities are seen.

Taking your statement at face value, as to not misunderstand you, (highest port velocities notwithstanding) here is where we disagree. Most of us here are aware the valve spends more time at low-mid lifts that max lift. As once stated, "One time to peak and twice through mid lift." This is supported by AUC formulas.

Gary

[SStrokerAce]

Well graph out a valve motion chart and you will be suprised at the amount of time the valve spends a different lifts... last time I checked the valve spent the least time at midlifts, most around peak (upper 10-15%).... there is usually a good amount of cylinder filling done at this time.

The funny thing is the low lifts sub .200 have some interesting things going on, overlap, high port pressures etc.... so sometimes more flow down here is not always the best thing.

I'll have to find where I put that writeup on the percentage of time the valve is at certain lifts.

BTW Darrin has pretty much said the same things I said in a post around here someplace.

Bret

[SStrokerAce]

Think I found it....

"Hyd Roller over .600 lift (.630 range) medium sized duration, sub 7500rpm and a "street motor"

.000-.100 68 degs 22%
.100-.200 40 degs 13%
.200-.300 26 degs 8.5%
.300-.400 34 degs 11%
.400-.500 32 degs 10.5%
.500-.600 60 degs 20%
.600 + 44 degs 14.5%

Now making a negative change in that motors flow curve from .200-.400" lift of 4.4% nets less than a 1% loss in max power and about .4% in average power. Now if you killed the flow at the top end (.600+) 4.4% you would see a 1% loss in average power. This is with big changes in flow of 15-20cfm at the top end. That's 150% more loss in average power.

To add a little more to this the lowest pressures seen in the port (highest vacuum) at the max VE occur between .420-.520" lobe lift (opening) and the highest pressures occur between .150-.020" lift (closing), from lowest vacuum to highest pressure there is roughly a 15psi change in pressures. The highest average velocities occured for 84 degs at lifts over .500". The more flow you have in that lift area will raise the amount of duration that the motor pulls that high of a velocity given the same sized port.

So you can see the time when the port is filling the motor the fastest is around max lift, and the time it's filling it with the most pressure is around valve closing while the piston is coming up the bore.

Bret"

Looks like the valve spends:

35% of it's time below .200"
30% of it's time between .200-.500"
35% of it's time between .500-.630"

So just in time/duration (they are the same things when talking about a cam) the midlift area of the curve is the part where the valve spends the least amount of time. It's suprising that the valve spends 35% of it's time in the top .130" of travel on that camshaft. Even if you limit the valve to .600" lift on a standard LS1 setup the valve spends a significant portion of it's time there. That's a lot of time devoted to a small area of lift. It's also the most common place for a LS style head to go turbulent at very high depressions. (which you say you have seen) So MOST guys aren't filling the port effectively in that area. This is mostly due to lack of attention to the short side radius.... too much velocity in the port at this point. That's a bad thing when the highest velocities and volumes are moved thru the port at these lift points.

The problem most people don't get is that the wave tuning effect of length and cross section on a port add a natural supercharging effect "resonance tuning" to a NA motor. This will make the pressures in the head port much higher than atmosphere (5-7psi) vs. the vacuum on the port will ever reach.

Originally Posted by Darrin Morgan
There are many proponents of the " flow curve must match the camshaft lift curve" theory but I am not one of them. Some people still believe that if the camshaft has a maximum of .700 lift that the area under the flow curve must be maximized in this area as well and anything that happens to the flow curve after .700 lift is of no consequence. Nothing could be more incorrect I assure you! Its like that old theory about 30 degree seats. They flow more down low ( .050 to .350 lift ) so they should make more power for cam profiles at or slightly above .400 lift because they maximize the area under the curve in that area,right? Wrong. You can put a properly designed 55 degree seat and chamber, decrease the flow at .050 to .400 lift and make more power with cams with only .400 lift. You have to design the thing correctly and its tricky. You cant just throw steep angle seats in any head and have this work. You must have convex chambers and good pressure recovery in the chamber or its disastrous. The steeper the seat angles and the larger the throat area, the more important the chamber design becomes.

You turn the air less, use less energy doing so.
You maximize the potential flow in an area more conducive to flow from a piston speed stand point.
You have proper pressure recovery in the chamber ( Equal exit velocity around the entire circumference of the valve head. A controlled deceleration of the air like a venturi divergent angle.)
You get more air fuel mixture in the cylinder.
It makes more power.

That's my theory and I am sticking with it until someone can come up with a better one.LOL
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines

[BillyShope]

If, instead of plotting flow versus lift, you plotted flow versus the camshaft (or crankshaft) rotation angle for the associated lift, the area under the curve might very well constitute a valid measure of a camshaft's effectiveness. This would be for comparative purposes only, of course.

(Easiest trick for "integrating" is to cut out the plots with scissors and weigh on a laboratory scale with sufficient accuracy.)

[gas]

Well graph out a valve motion chart and you will be suprised at the amount of time the valve spends a different lifts... last time I checked the valve spent the least time at midlifts, most around peak (upper 10-15%).... there is usually a good amount of cylinder filling done at this time.

Bret, I understand your reasoning above, but is that taking into account both sides of the lobe?

BTW Darrin has pretty much said the same things I said in a post around here someplace.

Think I found it....

Originally Posted by Darin Morgan
There are many proponents... That's my theory and I am sticking with it until someone can come up with a better one.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines

I am familiar with the above post by Darin, if that is what you are referring to, in regards to "Darin has pretty much said the same things..." However, as how I interpret what Darin posted, I do not agree it is referring to the same issue (cam lobes) that you are referring to.

The above statement I quoted above... "One time to peak and twice through mid lift", came from some guy named David. It can be a 'small world', so it's possible Darin may even know him. Now it is also possible, David has reconsidered his previous quote, and no longer endorses it, but I still agree with the logic he used, whether I've been 'snowed' or not. Bret, it hinges on the question I addressed to you above. Have a pleasant 4th.

Gary

[Ken_Parkman]

Also take note of the actual piston velocity in relation to the valve opening. At low valve lifts the piston velocity is low - or negative. It is only when the piston is significantly past tdc when it really starts to draw air, and therefore higher on the cam lift curve. A good percentage of the closing ramp occurs when the piston velocity is negative. On the EMC engine I spent a lot of attention on low lift flow, but I was not trying to maximise it. The engine rewarded me with a pretty good torque curve.

Each application is specific depending on cam, induction, desired rpm band, etc. But learning here and thinking about it has led me to the conclusion excellent low lift flow can be a bad thing - depending on the application. And area under the curve calculations can be deceptive as an induction system has very non steady-state pressures driving it.

[SStrokerAce]

Well graph out a valve motion chart and you will be suprised at the amount of time the valve spends a different lifts... last time I checked the valve spent the least time at midlifts, most around peak (upper 10-15%).... there is usually a good amount of cylinder filling done at this time.

Bret, I understand your reasoning above, but is that taking into account both sides of the lobe?

Yeah.... both open and close. This was a plot taken from a Cam Dr file so it's very accurate in terms of the theoretical valve motion.

The thing we have to remember when looking at valve motion in a graphic form (bell curve) is that we are not looking at a area, or area under the curve, but a plot of a motion. I think it's natural to see it as a area but that's not what is happening.

BTW Darrin has pretty much said the same things I said in a post around here someplace.

Think I found it....

Originally Posted by Darin Morgan
There are many proponents... That's my theory and I am sticking with it until someone can come up with a better one.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines

I am familiar with the above post by Darin, if that is what you are referring to, in regards to "Darin has pretty much said the same things..." However, as how I interpret what Darin posted, I do not agree it is referring to the same issue (cam lobes) that you are referring to.

I guess I read a lot into it, but esentially what I take from that whole statement is the flow curve is not the most important in the low and mid lifts.

The above statement I quoted above... "One time to peak and twice through mid lift", came from some guy named David. It can be a 'small world', so it's possible Darin may even know him. Now it is also possible, David has reconsidered his previous quote, and no longer endorses it, but I still agree with the logic he used, whether I've been 'snowed' or not. Bret, it hinges on the question I addressed to you above. Have a pleasant 4th.

yeah most likely he does know him lol

I think what Ken is hitting on also goes along with this. Where the piston is and what it's doing is very important as well. The only thing I would add to that thought is that the air/fuel fluid is not a string attached to the piston, I think people commonly see it as that. So when the piston is moving fast and changing the pressure in the cylinder, the air/fuel fluid is going to react but since it has mass there is a lag there.... what we should look at is the changes that the piston movement makes on the pressures in the cylinder compared to the port. This really brings the bad side of what having good low lift flow can do.... Overlap is probably the area where we find the biggest problems with low lift flow and it's bad effects on the port. I'd take 10cfm less at .050" if the port flowed much less the opposite way, keeping the polution of the intake port with exhaust gasses down. I think there is more TQ in the curve to be found there compared with the minimal increase in low lift flow. All depends on the situation also... Sometimes you need more TQ below TQ peak and other times you need more TQ above HP peak, if I wanted more below TQ peak I would work on preventing the polution of the intake charge, and if I wanted more after HP peak I would look at helping the overlap portion of the flow curve work to improve scavenging. That's just my thoughts on it....

Bret

[dwilliams]

(Easiest trick for "integrating" is to cut out the plots with scissors and weigh on a laboratory scale with sufficient accuracy.)

If you don't have a scale precise enough for that, you can use the "Monte Carlo method" of finding the area of an irregular area. Draw a grid over the curve, count all the whole blocks, then go around the perimeter and count the less-than-50% blocks as zero and the more-than-50% as full blocks. You can get well under one percent of error that way.

[UDHarold]

For the past 25 years I have based my cam design on one theory.
What happens before TDC in the intake cam is bad, and minimising the bad helps the engine breathe its maximum.
All the work done by the piston in starting airflow is done in the 1st 75* ATDC, up to the point of maximum piston velocity. From the point of maximum piston velocity on, the piston is progressively slowing down and pulling LESS hard on the intake port with every degree of rotation. Yet because of inertia, the velocity in the intake port is increasing, up to a max at BDC. If everything is done right, the cylinder is still filling when the initake valve shuts after BDC.
By minimizing Reversion before TDC, the piston starts airflow earlier, vs earlier intake valve openings which let in more and higher pressure exhaust gases. The less reversion, the earlier airflow starts after TDC. By having a cam with lots of mid-lift and high-lift area, the valve has more time(duration) to fill the cylinder with harder-flowing air/fuel(inertia ram).
The exhaust cam has its own part to play, I'll cover that later.
This has been my intake theory for 26 years.

UDHarold

[maxracesoftware]

For the past 25 years I have based my cam design on one theory.
What happens before TDC in the intake cam is bad, and minimising the bad helps the engine breathe its maximum.
All the work done by the piston in starting airflow is done in the 1st 75* ATDC, up to the point of maximum piston velocity. From the point of maximum piston velocity on, the piston is progressively slowing down and pulling LESS hard on the intake port with every degree of rotation. Yet because of inertia, the velocity in the intake port is increasing, up to a max at BDC. If everything is done right, the cylinder is still filling when the initake valve shuts after BDC.
By minimizing Reversion before TDC, the piston starts airflow earlier, vs earlier intake valve openings which let in more and higher pressure exhaust gases. The less reversion, the earlier airflow starts after TDC. By having a cam with lots of mid-lift and high-lift area, the valve has more time(duration) to fill the cylinder with harder-flowing air/fuel(inertia ram).
The exhaust cam has its own part to play, I'll cover that later.
This has been my intake theory for 26 years.

UDHarold

i totally agree with your Post.

---------------------------------------i have a lot of Dyno and DragStrip Data
from "before, under old NHRA SS Rules",
where you couldn't backcut valves
-to-
"after new NHRA SS Rules",
when you could backcut valves.

These SuperStock Engines were
Chevy 283's with 1.720/1.500 valves
Chevy 327's with 1.940/1.500 valves
Chevy 350's with 1.940/1.500 valves

Chrysler 318,340,360 with 1.880/1.600 valves
Chrysler 340 with 2.020/1.600 valves
very high velocity Ports, relatively small Port Volumes,
relatively small valve Heads.

100.0 % PerCent of all my Dyno testing so far
with the above Engines have ALL shown
HP and Torque Losses looking at Power Curves
"BELOW" the RPM point of Peak Torque
as Low-Lift Flow CFM is "increased"
by BackCutting or Porting Bowls differently.
These are Solid Roller Cams ranging from
272 deg to 286 deg @ .050" intake durations

around 4500 or so RPM, these Engines were about
dead-even in HP and Torque numbers,
but below 4500 RPM , and as you looked at
Power Curves towards 4000 or 3800 or 3500 RPM's,
you saw Torque Losses with "better Low-Lift Flow"
on these various SS Engines.

So far, 100.0% PerCent of Dyno testing has shown=>

1-Increase Low-Lift Flow = Loss of lower RPM Torque,
below the RPM point of peak Torque occurrence.

2-Increase Low-Lift Flow = sometimes more Hi-RPM HP,
and sometimes the Power Curve was widened a few 100 RPMs,
but never did i see more Torque at the very lower part of
the Torque Curve....increased Low-Lift Flow always
has "hurt" low-end Torque numbers ....with the Cams those Engines run.

Conclusion is, better Low-Lift Flow seems to
sometimes increase Hi-RPM HP,
and decrease or "hurt" very low to lower RPM Torque + HP
with those Engines/Cams.

Even on an off the showroom floor OEM Engine
that might have its RPM point of Peak TQ
ocurring at 3500 RPM...if you go and make
a substantial increase in better Low-Lift Flow,
i'm certain you will definetly see a LOSS in TQ
below 3500 RPMs !

------------------------------------------------------

Another relationship or another way at looking at Low-Lift Flow
or even some of Mid-Lift Flow=>

i can very easily make just about any
BigBlock Chevy Head w/2.300-2.350/1.880,
have much better Head CFM Flow numbers from .050",
.100",.200",300,.400",.450" Lift increments,
than a 500 cid NHRA ProStock Head.

this is my example point=>
an Edelbrock Victor Race head 2.350 Int valve 45 deg seats,
can be dead-even or better than a ProStock Head
with 2.525" 55+ deg seat angles between .050" to .450" Lift,
but,
the Edelbrock Head will never make 1400 HP on 500 cid N.A.
the Edelbrock Head might make 1000 HP or so at best on 500 CID
with the "same exact or better " Low-Lift Flow Numbers,
...so the Low-Lift and some of Mid-Lift Flow is not
overwhelmingly determining the amount of HP and Torque.

Where you do see a great deal of differences in Flow CFM Numbers
between the Conventional Style-Head -VS- the ProStock Heads
are in the "upper" Mid-Lift -to- High Lift Areas,
where a ProStock Head's Flow Numbers are a ton better,
and 300-400 HP better .

so "equal" Low-Lift Flow does not equal same HP or TQ
in same size CIDs...so Low-Lift Flow is obviously
not the "Controlling Factor".- in the reasons why
there is such a huge HP difference.
---------------------------------------------------------------

Mixture Inertia ram-effect combined with a positive pressure
acoustical wave, at around the time of .400" towards .050" Lift
or so , can be on average of 3 PSI or higher.

So if your Heads Flow Tested at .200" Lift were = 140.0 CFM @28"
...that same 140.0 CFM @.200" Lift may now be capable
of moving approx. 241.0 CFM @28"...about a 100+ CFM gain
from the above effects

so Low-Lift Flow will help you more at the Intake Valve
closing point at higher RPMs, and hurt you more at the
very Lower RPM part of Curve by increasing reverse Flow
or reversion at Intake Closing point,
and filling the cylinder too easily too quickly at the
start of the intake stroke at the lower RPM Curve.

you must need a certain amount of pressure drop
to create the great ram-effect at the intake valve closing point.
if you have too much low-lift flow too soon ,
you place a "kink" or hurt the formation of the depression
curve early in the stroke and hurt ram effect later at IVC

Where your Engine makes its Peak Torque,
is basically where your Engine is breathing its best,
after the RPM point of Peak TQ,
Cylinder filling is less and less.

Below the RPM point of Peak Torque occurrence,
there is not enough Int and Exh System velocities + Length Tuning +
due to CSA's and cylinders being fed too easily too quickly !
you are loosing your ram-effect at the IVC


Too much Low-Lift Flow can cause all kinds of problems
like reversion and overscavenging.
Increasing Low-Lift Flow is sort of like
increasing Cam's Duration at .050" and increasing
the OverLap Period....so that may force you to
use less Duration @.050" + spread Centers.

---------------------------------------------------------------

if you have a relatively lower RPM Range Engine
with good to great Low-Lift Flow,
you can or most probably need to shorten up
Cam Duration to offest the great Low-Lift Flow,
sort of like the Duration Numbers the 4 or 5 valve Head
engines have to use.

-------------------------------------------------------------

When i purchased my first FlowBench, a SF-110 in late 70's,
i immediately started trying to correlate what
Valve Lifts were important to gain great Flow Numbers at.
Going back and forth from SF-110 to DragStrip,
it started to show using .85% PerCent of the theoretical
Cam's Max Valve Lift.
Example=> .700" Lift Cam times .85% = .595"
or rounded-off to .600" Lift, so i made sure i had
great Flow in a .200" Lift range,
from .400" to .600" Lift Flow on a Bench for a .700" Lift Cam
or
from .600" to .800" Lift Flow if you had a .900" Lift Cam

later on with newer SF-600 Bench + Dyno tests + DragStrip test,
it looked more like .87 % was better to use..not a lot of difference.

By using at least a .37 Lift/Diameter Ratio Camshaft on Intake Side
and using .87% PerCent of that Lift to develope Heads on a FlowBench
has worked pretty well as a starting baseline.
The all-out max-effort 2-valve Head Engines prefer
at least a .39 to .42+ Lift/Diameter Ratios
with great Mid to High Lift Flow Numbers

Also i might add...with current technology
of "Lofting" the Valves...the .87% PerCent Factor i used
may be revised upwards to develope Heads on FlowBench
up or above the Cam's Max Lift point.

---Sorry for long Post