Posted by Sentinel on May 18, 1998 at 08:36:47:
T.O.O., (and all),
I'm still very intereested in headflow information. I came across some information that I'd like you to critique, if you would be so kind. The article was written with a particular type motor in mind, but I believe the information should be valid for about any 4-cycle motor. I deleted the references to the specific brand, since I feel they are irrelevant.
"...It is my intent to offer some vital information that may help those of you in search of the truth about the Airflow/Velocity Connection.
I feel it is imperative that I address the use of the flowbench in relation
to cylinder head conduit (often referred to as "runners"). In the early
to mid 1970's, many cylinder head porters (my self included) used a pitot
tube or velocity probe to discover high and low pressure areas in the runner.
While this is a great technical tool for
some data, there are far too many variables to consider in the intake runner for one velocity reading to accurately interpret the full extent of activity. A hand held velocity probe does in fact measure high and low pressure in the runner, and through mathematical equating, you can indeed calculate feet per second (fps). It cannot, however, relate to the fps that will result in the actual running engine without detailed dynomometer testing. The best you can receive is a mediocre comparison. A more sophisticated mathematical equation is needed to produce a more realistic result of the runner/running engine analysis.
General Motors, Ford, and Chrysler engineers, along with the most technological advanced race teams, utilized such formulas, thus analyzing all of the entire engine variables such as bore diameter, stroke, intended rpm, runner cross-section area (as an average), and finally the rate of expansion (roe). Very few people had access to these formulas. It was through the research and development of the high performance motors for many of the high-profile race teams during the early 1980's, utilizing my own dynomometer and designing my own flowbench that I came up with these valued or "secret formulas."
With the vast amount of flowbench testing I performed during the late 1970's, I learned a great deal using a pitot tube in relation to velocity. I made a much greater discovery than the fps using the wand, however, and that was the infinite number of velocities inside the runner. There are far too many velocities inside and around the port that you cannot use just one or two fps numbers to determine if a runner has a high or low velocity.
In the early 1990's I performed an experiment in which I took a [specific
head] cutaway and drilled six 1/4"
holes spaced evenly around the valve seat with 6" long tubes exiting out of the cutaway to be connected to six
individual manometer probes NOT protruding into the port. The data retrieved was completely accurate because the sensors were not an intrusion inside the port, but were strategically positioned at multiple points around the valve seat. The astounding information I learned was: (1)Each manometer read different pressures, (2)all of the pressures changed as valve lifts increased, (3)when the port was reshaped the numbers changed again, and (4)there are a minimum of three dominate streams - with one stream always more dominate than the others and that stream being the one that is the shortest on the floor (a)to the valve seat over the short turn radius, and (b)on a [specific] head.
Many other things were learned, too many to list, but here's an overall theory - with the different streams of air flowing at different speeds, vortices occur where the streams collide (different boundary layers) in the center of the runner, or thereabout, from the entrance all the way to the valve seat. If this is true (which I firmly believe after my 25 years of porting experience), than the technique to increase flow is: Balance out the streams to the best possible equalization of flow streams, set the main stream flow angle so that the dramatic ninety degree turn into the bore is as easy as possible (keeping fuel separation off the backside of the bowl).
When this is achieved, then and only then, can a velocity be averaged to apply the mathematical formula, to attain a "virtual" velocity so an optimum combination can be designed. Once this information is verified, the engine variables such as cubic inch, rod length, cam shaft lobe design, and header tube length will determine if a head has a high or low velocity."
Me again. I hope to someday be able to determine when someone, like this person, is legitimate or if they are "just blowing smoke..." I'm admittedly not yet at that point. From the above, do you see anything that would indicate whether this person should know what they are doing, or are they just garage hackers that know some buzz-words?
Posted by T.O.O. on May 19, 1998 at 15:44:47:
I’m going to attempt to respond to the post by Sentinel, and do so in
such a manner that I don’t start some pissing contest. My only response
to the information posted is that it’s in many ways accurate, and I’m sure
that if the man’s been in business all these years, his work must do something
First off, when you’re dealing with air flow, you’re dealing with fluid dynamics, and all the laws apply, however, air is both elastic and compressible and these qualities cause the science of air flow to be unique.
With the exception of the exhaust side, we’re not simply dealing with air flow, but we are working with wet air flow, and that’s an entirely different animal, because, assuming that the fuel is well atomized we’d like to keep that mixture in that state while it travels to the cylinder. It’s up to the manifold and port runner / seat / combustion chamber shape to keep the mixture correctly suspended. We all know that fuel is heavier than the air that’s carrying it, and we all know that when turning, the light weight mass will "hug" the inside of a turn, while the heavy material will tend to separate and go to the outside of the turn. Now this is problem enough in ideally configured runner / ports, however, unfortunately, we rarely are able to create ideal rules for our heads to run legally, so missing a push rod here, and making room for a head bolt there simply compound problems, as the route to the cylinder now has some more turns in it. How do you keep the mixture suspended in turns? Well, the only way I’ve ever known is to slow the mixture enough to prevent separation, and re-accelerate the charge when the path straightens out by decreasing area. As we’re changing areas in the port to maintain mixture integrity, we are also changing the pressure. Low velocities yield high pressure, and high velocities will lower pressure, and if proper attention is paid to the runner / port shape, it’s possible to make the mixture velocities work for you.
For many years people have been sticking probes down ports on the flow bench to find the areas of highest velocities, and the mere presence of the probe can alter the flow in the port which has led to some nifty fixes over the years. The goal in probing ports was to find these velocities or hot spots and contour the area to increase the flow, and we’d often "map" sections of the ports every .100" an record the data. The ports were then filled with an RTV like rubber, and a male mold would be available for sectioning every .100", and the slice or cross section would be transferred to a work sheet, a line carefully drawn around it, the cross sectional area measured with a compensating planemeter, and the velocities and pressures "mapped" in each quadrant and the center were then written on the port slice. I used to do that with every port, and it worked well because you could relate velocity and pressure to area at almost any given point. This information from thousands of molds and flow tests is what I began assembling on a "powerful" pc. (during my two year vacation with cancer ’79 -’81). What I finally developed was a soft ware / program package that would design a port for you if given the proper inlet size, port length, and valve size. I called this system "design by area averaging", and it worked very well. When DEC made some hardware available and true 3D software was available, we jumped on it, and after inputting all our data, and allowing the system access to some new information, we finally had the ability to allow the computer to design the ports.
Back to the subject. Using my "mapping" system allowed me to place vortex generators here and dams there to keep the mixture as centered as possible. I did this because, if there are many different flow "streams", you have a shearing that will take place, and the first victim is the fuel in the mixture, as it’ll be pulled from the air and proceed as a liquid, and that doesn’t burn well. I’ve addressed the topic of air flow before, and I believe I’ve always told you that it’s easy to calculate how much air an engine of a given displacement will require at any given rpm. I also recall saying that more than enough is too much, as area will be too large and velocities will drop. Flow quality is what it’s all about, as long as you have sufficient quantity.
There are some archaic formulas that some OE engineers used to get in the ball park, but the fact that none of the big three could design and flow ports on the computer says volumes about how well their formulas worked…and they weren’t complex.
I’ve also said that ports flow both directions !!! And they indeed do. During overlap and at the point of intake valve closure the flow spikes back up the intake port. Now since the reversion during overlap is basically inert you can’t burn it again, and any time there’s a large pressure spike (from valve closure), the mixture that was headed to the port via inertia is adversely effected to say the least. My fix for this dilemma is the design of the intake valve seat. The configuration of the intake valve seat and the valve itself can minimize, if not stop the reverse flow problem. There are formulas I’ve written to define intake seat / combustion chamber shape, and they are not complex at all. They were developed time an time again as I was doing heads, and the only real reason for writing a formula was to make it a little faster setting up machinery to go from a valve that was 1.22" in diameter to a 2.625", and the later was not for a Honda. Since we now use CNC machinery, the formulas are a help when writing the program.
A large intake valve or an intake port that flows great at mid to high lift, doesn’t have low lift flow worth a damned if I designed it. During my attempts to discourage reverse flow on the inlet, I found that any port that flows well at lower lifts will flow backward with even greater efficiency. So attention to seat configuration kills low lift flow, in order to discourage reverse flow. If I could design a port / seat configuration that would flow "0 cfm" at low lift I’d be happy. The seat configuration that I use is only concentric on the angle that the valve actually seats on, and the top angle is the combustion chamber. Below the seat angle the inside diameter of the seat insert is not round and it is a continually changing radius in section view….no three or five angles here. The "seats from hell", as many customers call them, are configured in that manner to deal with the changing velocities and pressures encountered as the valve opens and closes. The seat is probably the single most aspect in porting, as it’s the transition from port to chamber / cylinder, and if you’ve done well to this point with mixture composition, this is where all your hard work up-stream will be for naught, if not properly done.
I’m not sure at this point that I have addressed the post. As I said earlier, I’m not trying to piss anyone off, but some of the revelations regarding dominant steams, pressure differentials about the seat and in the port are pretty elementary at best, but he does tell you what I’ve said from day one relative to flow: It will seek the shortest route through the port possible.
I’ll end my talk with this comment on "virtual velocity"…."Once this information is verified, the engine variables such as cubic inch, rod length, camshaft lobe design, and header tube length will determine if a head has a high or low velocity." First off, the displacement, rod length, cam design, header length, and port configuration (high velocity vs. low velocity) are not variables. The dimensions of these components is how you "design" the engine to operate in the manner you intend. Designing components and matching them correctly ….building engines is not a crap shoot. You can be smart and look carefully at all the pieces so they all fit the master plan and then you can dictate the way the engine runs, or you can do it the "other way" and let the engine dictate the way it runs (or doesn’t). Why do you think that there will be so many components in the blower kits? Because I’m going to dictate the way all the cars run….it’s the total package.
……………………………………THE OLD ONE ……………………………………
Posted by T.O.O. on May 20, 1998 at 18:35:13:
In Reply to: Do Beans Cause Pressure, And Does Pressure Cause Wind ? posted by body on May 19, 1998 at 15:44:47:
I hope I was able to shed a little light for you. The importance of
flowing back as well as forward absolutely can not be something a cylinder
head business avoids. It has a tremendous effect on "what happens" at overlap,
and, therefore, camshaft events. As this is the subject for some more of
the "World Series", I'll stop here.
You are very wise to point out that that I've experienced many, many failures during my ventures with "all forms" of engines. One thing that has led to folks like Penske calling my work the "Rolex" of the industry is the fact that everything I sell has to meet my standards, not my customers'. I believe we know more in several fields of specialization than anyone on any race team and also various OE manufacturers. The fact that all the different components have to work together has made us the "crew chief and manager" of not only the engine programs, but we're always involved in car set-up as well. Many people simply don't understand how to work with the torque curves we provide.
Back to failures, then I must go. There have been many instances early on when a "name" racer would come and offer to put me on the map. I'd buy head castings and, using the most sophisticated flow bench to date, would set about working on a "killer" set of heads. After over a week, I'd have all the intake ports flowing within .5% at every .050" lift tested, but (I'll never forget this) I had one exhaust port that was about 2.0% off, and I wouldn't allow the racer to "use" the heads. While he was racing (and winning) in Pamona, I worked to find the problem, and it was a seat width that was .002" too great, and once fixed that port out flowed all the other "good" ones, so I fixed them all, which screwed my flow relationship with the intake ports, and on and on. The racer stopped by on his way back from winning Pamona and asked me to flow the winning heads he'd had custom done. My answer was "yes!", and we flowed them and they were absolute crap compared to the heads I wouldn't allow him to have(before the exh. fix). I let him have the heads and he rewrote the record books all season. The point of this wandering story is that nobody gets anything inferior from me, and on failures....many claim that I can snatch victory from the jaws of defeat, and it's true to a point. I simply believe that as long as you take the time to analyze all the numbers, there may be something other than torque that you achieved and it's worth a look. I also must find the reason that the torque wasn't what I'd thought it should be, and that turns the "failure" into a learning process, so the knowledge curve is always headed up. Life is a balance, life is also like a sine wave, the trick is to turn everything into a learning experience, and that's positive motion. Now, if you take this approach, and if you put 100% into what you do there's no such thing as failure, and suddenly the base line is tilting up rather than staying horizontal. The next thing is to attempt to reduce both the frequency and amplitude of the waves. Now that the base line is going up, when you hit bottom on the next wave, you don't go as far down as earlier, and you may succeed in only dropping to the "highest" level of the curve, one wave previous. So, yes, I've had many failures the way most people think, but I've had very, very few when I look at the picture....when you learn, you've not failed.........................think about it.