May 2008 was something of a milestone for me as far as the modification of cylinder heads for more performance was concerned. It was 50 years since I performed my first cylinder-head flow test. The technique I used was crude, to say the least, but it worked. Looking back on it many years later, I realized I should have continued flowing heads using this original method, instead of being swayed by convention. My original method employed the floating pressure-drop measuring method described in Chapter 2. This was not because I had, even at the tender age of 15, figured out that a floating pressure drop was better; it was because I had no idea how else to do the job. But as events unfolded, I flew into the face of convention for one of the first times as far as high-performance technology was concerned, but it was hardly the last!
This Tech Tip is From the Full Book, DAVID VIZARD’S HOW TO PORT & FLOW TEST CYLINDER HEADS. For a comprehensive guide on this entire subject you can visit this link:
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Here is how events unfolded. The first flow bench was, in fact, my mother’s vacuum cleaner. I mounted the head to be tested (an A-Series head as per the Austin/Morris Mini engine) on a bare A-Series block. The head was equipped with a way to precisely open the valves. Then, for the intake tests, the suction side of the vacuum cleaner was located in the bottom of the bore and sealed, so there were no leakages at this point.
Next, a spark plug with the middle removed and a piece of 1/4-inchdiameter copper tube glued in was installed into the spark plug hole. It was connected to a manometer, made of clear plastic tubing stapled to a 2 x 4-inch board. This was marked out in inches from –48 inches at the bottom through zero to +48 inches at the top. The plastic tubing was looped, so that the bottom of the “U” was formed about a couple of feet or so below the bottom of the 8-foot-long 2 x 4. A section of the U-tube was filled with food-coloring-dyed water until it reached the zero mark.
As you can see from Figure 3.2, there is not much to this bench. It can be constructed in a few hours for a minimal expenditure. If you already have a shop vac, the rest of it costs probably less than $75.
Here is how it works. The more open the valve is, the lower the pressure drop is, as measured by the manometer. At low valve lift, say, 0.050, the manometer can read (depending on the vacuum cleaner’s capability and the valve’s ability to flow air) anywhere between 60 and about 100 inches H2O. If the flow at a given lift is improved, the manometer reading at that lift drops. Let’s say that the stock head at 0.050 valve lift produced a reading of 80 inches. We then do some seat blending on the valve and head casting, and on the next test the manometer reading is 70 inches. This means the flow has gone up, so the pressure drop pulled by the vacuum cleaner is lower. To a first approximation, the flow has increased by the square root of 80 divided by 70. That works out to 1.069, or a 6.9-percent improvement.
You can see that this bench primarily tells us whether or not the port is flowing better or worse. Also we can see that it does not test the head at a standard pressure drop, as does almost every pro-built bench. This standard pressure drop, as previously stated, is considered conventional practice and allows a uniform method to be used for quoting the CFM of flow produced.
At this point, you may be thinking that not having the ability to determine the CFM is a small price to be paid to establish positive or negative trends in a head’s airflow capability. After having built my bench, I spent a couple of years wondering how I could get real CFM numbers off it, so I could swap flow bench war stories with the guys at Weslake (the big name in airflow at the time) with-out revealing both my youth and then-amateur status.
As far as CFM measurement was concerned, I saw the light some years later during a conversation with an engineer who was somewhat older and more experienced than I. During our conversation he used some key words: “standard pressure drop.” Well, there we go—I realized that I could adjust the test pressure/vacuum so that it was a constant; and then I could calculate the CFM. It was not quite as easy as typing the words but that, in essence, was it.
Over the next few years, I built increasingly more sophisticated benches until finally, during the early 1970s, I built a bench that conformed to British Standards for precision gas flow measurement. It was a 15-foot-long monster. It worked just fine and cost a small fortune but the payoff was a lot of flow work that was done for those porters who didn’t have a bench. In the late 1970s to early 1980, I even did some work on it for the McLaren F1 guys.
A Rethink on Matters
By the time the mid 1980s came around, I began to have second thoughts about using a standard pressure drop to test heads. The issue here was: What sort of pressure differences do we see between the port and cylinder on a live-running race engine compared with what was typically being used on a flow bench? In Smokey Yunick’s Power Secrets, the author went to some length to make sure we understood that a seemingly magic 28-inch pressure differential should be used. That, as of 2012, is practically an industry standard. But as I have already pointed out, a race or even a high-performance street engine does not see a fixed standard pressure drop. Here, we need to deal with the reality.
The induction system on a true race engine is, for the most part, exhaust driven. That means the scavenging pulse from the tuned exhaust pulls a far bigger depression in the cylinder than the piston pulls going down the bore. On something like an engine from NASCAR’s Cup series, this can amount to 120 inches or more at TDC during the overlap period. The draw on the intake port at TDC can be such that, even though the piston is virtually parked, the intake charge in the port can be moving into the cylinder at as much as 90 mph!
When the valve is near wide open and the piston is traveling at peak piston speed (this is between 72 to 74 degrees after TDC), the draw is somewhat less. How much less? For a typically high-flowing two-valve head feeding about 1.2 cfm per cubic inch to the cylinder, the pressure drop is about 15 to 20 inches H2O at peak power.
The red curve in Figure 3.4 is a smoothed curve of the pressure difference between the cylinder and the intake port throughout an induction stroke. Although the curve can vary quite substantially from one similar engine to another (due to relatively small changes in lengths, diameters, and cam characteristics), this curve is representative of a 620-hp, single 4-barrel 355-ci motor.The first point of the graph is that the draw on the intake valve/port is greatest at low lift, in which the suction reaches 100 inches H2O while the valve is at just 0.050 lift. This means testing at 28 inches at this low valve lift is far from representative of the real world. Therefore, your floating pressure-drop tests should use a high-pressure differential at low lift and a lower one at high lift.
All the forgoing leads to one conclusion: To more nearly simulate what happens in a running engine, intake flow tests need to be done at a high pressure drop at low valve lift and a lower one at high lift. This is exactly the situation that happens with a flow-test rig (Figure 3.2). An uncontrolled vacuum source, such as a shop vac, pulls a large vacuum when the intake valve is closed and a progressively lesser vacuum as the intake is opened. So running a floating pressure drop, as we are doing here, is actually a more realistic simulation of what happens in real life.
At this point we have, with a floating pressure-drop bench, a flow testing situation that more closely mimics the pressure differentials seen in the cylinder/intake port of a running engine. So what are the advantages? Let’s quickly go through them again to be clear on the justification for adopting this procedure over the more normal fixed pressuredrop method.
If the pressure drop is too low, the flow pattern that develops in the port, especially in the more critical regions close to the valve seat, is not the same as at the higher pressure drop seen in a running engine. If we use a pressure drop that is too low, the flow attaches itself to the port wall on critical curves, such as the short-side turn, without any significant flow separation.
When these conditions exist, air is fed to the part of the valve circumference that is situated adjacent to the short-side turn, so that the flow is better than it typically is at a higher pressure drop. When the pressure drop is increased to something more nearly representing that seen in a running engine, the port velocity increases to the point where the air simply skips off the short-side turn and tries to exit the valve on the long side. As a result, a considerable section of the intake valve’s circumference experiences very little flow.
If we take a low standard pressure drop test of, say, 8 inches and correct it to 28, the resulting number comes out higher than if we had flow tested at 28 inches in the first place. In practice, if pressure drops significantly below 8 inches are used, the flow in the port slows enough to stay attached even around a relatively tight turn.
Running the flow bench tests and conducting high-to-low floating pressure-drop tests creates the same pattern of flow-reducing portto-wall separations that occur during real-world running conditions. From this, it follows that the most effective port modifications are achieved by addressing real-world flow patterns and improving the port shape to improve such patterns.
The bottom line is that our cheapo flow-test setup is actually a better tool for developing an intake port than a $10,000 commercial flow bench used in a conventional manner. At this point, the only down side is determining just how many CFM the head is flowing when each reading is corrected to the common 28-inch pressure drop. Without this number, you won’t be able to make a comparison with other flow test results or be able to compare your work to others. This can be fixed relatively easily, but for now let’s consider the exhaust.
Flowing the Exhaust
Without making some fancier test equipment, we are not going to be able to flow the exhaust at reallife test pressures. Typically, when an exhaust valve opens, the cylinder pressure is somewhere between 70 and 120 psi. If you are intent on having a pump that develops this kind of test pressure, even for just the low-lift tests, be aware that you need about a 200-hp motor to drive the pump. Very few flow bench setups are capable of this. Although unconfirmed, I have heard that Ford’s Detroit division has a flow bench that can approach real-world pressure drops, and that it costs a mere seven-figure number to build. For the most part, we flow the exhaust at 28 inches and live with the fact that it is not the best way to do things.
However, our budget bench, with its uncontrolled floating pressure drop, actually does a better job than a commercial bench at a fixed pressure drop. I can say that there is little to prevent using a commercial fixed-pressure drop bench, such as the SuperFlow 600, in a floating pressure-drop mode, which I address in Chapter 3.
My friend Roger “Dr. Air” Helgesen built a bench that worked along the same lines as this in the early 1980s and still uses it today to flow heads and intake manifolds. As usual, Roger adopted a singularly simple way to convert the pressure drop seen on the manometer to CFM at 28 inches with nothing more than a sheet of graph paper and a few calibration orifices. Just how this is done is our next subject.
Establishing the Numbers
Okay, so you have built a budget flow bench. While this may allow you to establish whether a move has increased or decreased airflow, it does not, at this time, allow you to compare your efforts with the rest of the head porting community. Within reasonable limits, that problem can easily be taken care of.
When using my early flow bench, I never made the connection between using a floating pressure drop and actually calibrating the setup to give CFM. Instead, I invested a lot of hours building my monster British Standards bench with all the corrections then known to man. A venture like this is not the sort of job I recommend to other would-be porters/ cylinder-head development engineers. Your time is better spent on developing heads and selling what you are producing. Doing otherwise means investing what is potentially a huge amount of time, effort, and money in a bench that, at the end of the day, serves you less effectively than the super-cheap floating-pressure-drop one I advocate here. However, if you want a little more than just a vacuumcleaner-powered bench for a greater range of pressure drop, by all means build it with more powerful motors.
But let’s get back to reading out our results in CFM. Here’s where the revelation came in. For many years, I knew Roger Helgesen had a flow bench but the deal was we always hung out at my place (maybe that’s because the Serdi seat and guide machine was there). But one day I was at his house, where he had his flow equipment, porting bench, and tools. What an eye opener that was. If ever there was a guy who could come up with ultra simple ways of doing ultracomplex jobs it was Roger (Another good friend of mine christened Roger “Dr. Air,” and I always thought that to be a very appropriate moniker).
What really caught my attention was the calibration plate Roger had made and the graph he was using to simply read off the CFM at 28 inches of depression. The plate is shown in Figure 3.5, and the dimensions to produce it in Figure 3.6. It has holes sized to flow 5, 10, 20, 40, 80, and 160 cfm at 28 inches of depression across the plate. Not only can you use this plate to figure out how much flow is passing through a head on a floating depression bench, but you can also use it as a reference tool for a regular bench, such as a Superflow.
A few words about producing or acquiring a Helgesen plate: With Roger’s kind permission I have reproduced the dimensions here, so you can make your own. I trust you to not go into production with these and sell them. It is Rogers’s idea and I ask you respect that. If you are not in the position to make one, you can check to see what the availability is through Dr J’s Porting Supply.
Let us assume at this point you have a plate; how is it used to give CFM at 28 inches? Here is how that is done.
Step 1: Make sure your bench is sealed so no leakage takes place, except through the test piece. Position the Helgesen plate on the bench with all holes plugged with clay (or any convenient plugs).
Step 2: Start with a reading on the manometer, with the plate completely blocked off for a “zero flow” depression test, and note the pressure drop seen on the manometer. Note this stalled depression. (If you did not make your manometer tall enough, the vacuum cleaner has now drunk all the water from it!)
Step 3: Open the 5-cfm orifice and note the depression (when I was talking about machining this plate they were referred to as holes—now that we are flowing through them they are orifices).
Step 4: Plug the 5-cfm orifice and open the 10; flow test and note the depression.
Step 5: Open the 5and 10-cfm orifices together and again note the depression. Continue in 5-cfm increments until all the orifices are open and you have recorded the depression at each 5-cfm increment.
Step 6: Get a couple of large sheets of graph paper, the larger the better. I recommend something like 20 x 20 inches. Then for the intake, make a graph as shown in Figure 3.7.
If you plot out your results, you should get a similar curve. Where it starts and finishes is totally dependent on the vacuum/pressure source you are using.
Step 7: When you have a curve for the intake, repeat the test but use the blower side of the vacuum cleaner and reverse the plate.
Step 8: Blow through all the holes in the same progression used for the intake and make a graph for the exhaust.
You can now flow a head and get some respectably accurate flow figures for comparative purposes.
Although what we have done here is very basic, it can produce results comparable to benches costing $10,000 or more and considered the industry’s standard. There are, however, many points at which errors can creep in and considerably reduce the accuracy of your results.
Let’s start first with leakages. For the numbers to stand even a halfway decent chance of being accurate, the bench must not leak at any point.
The voltage input to the motor influences the amount of suction a vacuum cleaner or any electric air mover can produce. You must monitor the voltage at the motor input and make sure you test at the same voltage each time. For the record, Dr. Air has a step-up transformer that increases the line voltage from whatever it may be (it varies between 110 and 115) to 130 volts, and then a rheostat device is used to adjust it to 115 volts.
The way the calibration plate is mounted on the flow bench also affects the readings. The ideal situation is to mount a box, which can be made of wood but must be airtight, about 9 inches down each side (9 x 9 x 9) with a 5-inch hole in the top, and whatever size hole mates up to the block or whatever you are using to simulate a block. Place the calibration plate directly over the 5-inch hole in the box and flow test it. If the plate is mounted on top of a bore even as large as 4 inches, there is a residual effect from the downstream velocity of the air and the plate flows about 2 to 3 percent higher than if flowed into an open box.
Big changes in temperature and pressure also affect the reading, but this is only minor if the bench is in a constant indoor temperature. If there is any doubt about the figures, recheck the depression with the plate at, say, 160 cfm. Using this reading, correct the numbers up or down by whatever percentage of error is seen.
Note: When the depression falls between 160 inches and 15, the highest degree of accuracy is achieved. If the depression drops much below about 6 inches at high valve lifts, you can figure that when corrected they could read a little higher than they should. Just how much is dependent on how severe any flow separation on the short-side turn is at the higher pressure-drop readings I am advising you to use.
If you have built a bench along the lines I’ve suggested, then at this point, you have a bench that was cheap to build and can deliver CFM numbers. The next step for an upgrade here is to write a spreadsheet program that does the number crunching for you. I have written a relatively simple Microsoft Excel program that allows me to input the depression numbers into my computer and subsequently prints a professional-looking set of graphs of the flow tests, complete with my business details along the top of the paper.
You may say that’s all well and good, but I am not into writing my own programs. That is not really a problem. But whether you can write programs or not, I have a simple question here: How would you like to upgrade what we have built so far with an electronics package? Such a package costs about $1,000. It allows your bench to read out in corrected CFM and directly integrate with your computer, so you can do fancy printouts. Sound good? Well, in practice you have two companies that I know of that can be of great help with this, so that’s our next topic.
Okay, you have built the budget flow bench detailed so far. While this may allow you to see moves/ alterations that help or hinder and to determine CFM flow, it does not necessarily allow neatly printed comparisons of your efforts with the rest of the world. Nor, without considerable programming yourself, does it produce an analysis of what has been achieved such as flow efficiencies, port velocity, velocity gradients, and the like. Although there may be others, Audie Technology and Performance Trends are two companies I have dealt with that have very cost effective products that are professional quality but well within the reach of the home-based porter.
Budget Bench Electronics
Let’s look at how to take the floating depression bench just described, and substantially upgrade it to a professional-grade piece of test equipment. This includes an electronic readout in CFM, pre-corrected to the depression of your choice (probably 28 inches), and that alone might convince most of you wanting a more up-market bench to take the plunge.
But that is far from all that is dealt with here. If you hook up your bench to a computer, you can record data with a push-to-read button that, while held down, averages the readings for as long as you do so. In addition, the system can also screen-display graphs of your porting efforts as well as print out professional-looking reports with your name on the top of the sheet (customers like this). Probably the best news is that you are only out of pocket by about $750 or so in 2012 dollars. If all this sounds appealing, let’s make a start on why and how to get from here to there.
You don’t need to have moved that much up the ladder from novice to realize that maximizing power means maximizing cylinder head capability. Everything else in the loop is developed simply to make the most of the cylinder head’s capability.
If we further analyze the performance equation, we find that at least 70 percent of a cylinder head’s performance capability is airflow related. The upgrades and accuracy tests, which I conducted with the aid of engine builder/tech writer Bob McDonald, brought our floating depression bench to full professional capability. This allowed it to meet the needs of those who port and prep high-dollar, four-valve heads for equally high-dollar clientele, as well as the more regular home-porter applications. But, in our case, meeting the needs of a high roller is maybe not quite as important as meeting the needs of the racer on a tight budget, and that probably includes most of us.
Plenty of drag and circle-track race classes limit head castings to less-expensive, production-style items. This puts a greater emphasis on even small flow differences; and if you want to win, it’s important that whatever you have is better than whatever your competition has. Though it’s not the only category to do so, the IMCA racer in the United States falls squarely into this group. Since the engine can be claimed for a fixed fee, it’s good to get power without parting with a bunch of cash.
If you are building an engine for this or a similar class of racing, you have to ask yourself: Just how much money can I afford to give away to be competitive? Like it or not, time and money are closely linked. We may resent giving away a pair of heads with an $800 porting investment, but not feel nearly as bad parting company with similar heads we have personally spent 10 to 15 hours porting. The bottom line is: Most racers have far more surplus expendable time than surplus expendable income!
You don’t have to tour many head shops to realize the most popular bench used by pros is the SuperFlow 600—possibly with electronic support. You probably also understand the reason you don’t have one of these benches is because it can cost as much or more than the race car you are planning to build. So, for most racers and enthusiast engine builders, a $10,000 to $15,000 bench is simply out of the question. The electronic support system I am going to cover is not.
Within pro engine/cylinder head circles, Audie Technology is well known. This company produces, among many other things, the Flow Pro data acquisition unit that is an add-on for non-computersupported benches such as the big SuperFlow units. It also produces the cost-conscious Flow Quik, which sells for about $750, and is not a flow bench in itself but more a means of measuring flow. By adding this unit to an existing flow bench, we can achieve as much as can be done with a commercial flow bench but at a fraction of the cost.
Accuracy and the Budget
Any piece of measuring equipment that comes in at less than 1/10 of the cost of its principal competition might rouse some concern about functionality and accuracy. Since the Flow Quik is a measuring instrument, tech writer/racer Bob McDonald and I decided to put it through its paces and pass on that info to possible end users. Our plan was to check ease of use, repeatability, and, most importantly, overall accuracy. To expedite matters, Audie Thomas of Audie Technology shipped us the Flow Quik unit the company exhibits at the Performance Racing Industry show. Bob and I extensively tested it for a full week and what follows are the results.
Introducing the Flow Quik
Audie’s show unit has a dummy cylinder mounted on a flow box. This is connected via a 2-inch-insidediameter (I.D.) hose to the tube containing the measuring device. Upstream and downstream of this orifice is a pressure tap, which is connected to a box of electronics. The pressure transducers in this box convert air-pressure signals to electronic signals. These signals are transmitted to a microprocessor and the data is displayed as CFM on an LED readout.
The first tests we ran were to compare the end results of a run at 28-inch fixed-pressure drop and another run with a floating pressure drop. To do this, we ran the bench both ways and used our Helgesen calibration plate as the test piece. In the floating mode, the test pressures seen on the bench by the Flow Quik ranged from about 72 inches to less than 10. The resultant corrected numbers and the accuracy produced (compared to corrected 28-inch numbers) are shown in Figure 3.15.
A calibration tube, which is installed in the system, is supplied with the Flow Quik. The readout is adjusted to 80.9 cfm on the 28-inch scale. In this instance, the unit was calibrated with the 80-cfm orifice in our Helgesen calibration plate, hence the zero error at that point. As far as overall accuracy, it is far better than the majority of benches in the performance world. Compared with a typical commercial bench, the Flow Quik, from 40 cfm up, averages about the same error; i.e., about 2 percent.
Although overall accuracy is important for us to make comparisons from different benches, the number-one requirement for a head porter is consistency from one month to another. We were able to make a relatively good check of that because of a dramatic weather change during our testing period. Readings taken seven days apart showed the Flow Quik’s repeatability to be about 1 percent. At the end of the day, we can say that the Flow Quik’s accuracy against a calibration plate was as good as a bench costing ten times as much.
At this point our tests turned to determining just how well, given the floating pressure drop, the Flow Quik’s performance translated into accurate and repeatable results on a real head. The LED readout on the Flow Quik box is only one function of it. This box has connections to allow the output from the microprocessor to be input into a computer. Also a push-to-read or take-reading button can be used to transfer the measured CFM to a Flow Quik program.
The Flow Quik program allows the user to type in info relative to the head being tested. This head-spec info is then used to calculate many factors important to the serious head porter. Such things as valve discharge coefficient and port velocities at various pre-determined points are calculated and displayed. The take-reading button also greatly improves accuracy and repeatability by virtue of its averaging capability. For our tests, a 5-second interval was used as the averaging period.
To put the Flow Quik through its paces, we used a Holley 23-degree, high-performance street small-block Chevy head. This pushed the Flow Quik to what we perceived to be about 80 percent of its limit with a dual motor-vacuum source.
Although installing the test head on this bench was the same as with any other bench, there was a difference from, say, a SuperFlow bench: The Flow Quik does not directly sense and compensate for any extraneous leakage. Although leakage at any point other than the intake valve can be deducted from manual readings, the same cannot be done in the computer-supported mode if accurate number crunching is expected. This means making sure there are no leaks in the equipment itself. And because the test depression goes so much higher than on a regular bench, the springs holding the valves closed must be at least twice the stiffness.
Test Pressure Comparisons
Our first tests with the Holley head were made in floating pressure drop mode. This allowed the Ametek motors to pull whatever maximum test-pressure differential they were capable of. At 0.050 inch lift, 62 inches of vacuum was seen across the intake valve of the test head. As the lift increased the pressure dropped; so at 0.700, it was down to just more than 12 inches. Several tests run under identical conditions showed readings spanning less than 1 percent.
Our next test was designed to simulate a lesser pressure/vacuum source. To do this, we introduced a fixed leak prior to the measuring point, to bleed off some vacuum.
Executing the same test but with about half the vacuum, and comparing the readings with the fullvacuum source, produced the results shown in Figure 3.15. You can see the microprocessor computations compensated and corrected, to within a close margin, for the difference between the floating test pressure and the 28-inch fixed test pressure. Comparing these numbers with those achieved from a freshly calibrated SuperFlow 600 (using a fixed 28 inches) we saw a maximum difference of 2.8 percent below 0.200 lift and 2.2 percent above. The average difference from 0.050 to 0.700 was only 0.9 percent, with the Flow Quik showing slightly more flow than the SF 600. The bottom line: Our test Flow Quik unit produced figures (which could be expected to vary a little from unit to unit) that are closer than typically measured between two conventional and supposedly identical fixed-depression benches.
The Shop-Vac Test
The last and, from our point of view, the most important test was to run the Flow Quik with a regular shop vac. Since the point was to see if a typical vacuum cleaner could be used, it was not part of the plan to get the biggest one we could find. The goal was to see if we could get respectable CFM readings with an average shop vac. Figure 3.16 shows that this is possible.
Our first thoughts on the performance of the Audie Technology Flow Quik were that it far surpassed expectations. Ease of use, speed, and accuracy were far beyond what you normally expect of such a cost-conscious unit. In its least expensive form, the unit from Audie sets you back about $650. Add to this the cost of building the bench as detailed earlier, a dial gauge, and a means of opening valves, and you are in business. If the shop-vac selected is about 6 hp, like a big Sears unit, I estimate a realistically accurate range of flow capability of about 330 cfm. Think about this: You can have a professional-capability floatingdepression bench for under $750. Port two sets of heads, and you have more than recovered your investment!
Another recognized name for flow bench testing is Performance Trends. In fact, SuperFlow resells Port Flow Analyzer software, Pitot tubes, swirl meter, and other accessories with its flow benches.
Performance Trends offers a couple of options for the DIY flow-bench builder: Port Flow Analyzer software and Black Box II electronics. These can be fitted to almost any type of DIY bench, even older SuperFlow, JKM, and FlowData benches. Their sales and tech staff ensure that you get the correct system for your DIY bench.
Performance Trends also offers calibration services for a small charge; you simply provide them flow readings from your bench with orifice plates of various sizes. Using this data, they tell you the full-scale CFM readings for your particular bench; so your bench, with their software, now matches the rest of the industry.
For those who want to start building a bench from scratch, Performance Trends offers a system called EZ Flow for about $999. This kit includes software and electronics, and plans for building a bench from PVC tubing. PVC tubing and fittings are especially suitable because they are inexpensive, easy to work with, and they do not leak. That is a good point because the major drawback of a DIY bench is air leakage. Unless multiple layers of paint are applied, significant amounts of air can leak right through plywood if enough care is not taken during prep and assembly.
EZ Flow kits come in two sizes, for either 4or 6-inch PVC. For flows up to about 150 cfm, the 4-inch system works fine. For anything greater, up to around 500 cfm, you need to build it out of 6-inch PVC.
The EZ Flow system also includes critical machined components, the flow orifice, and the head adapter. If you don’t have a machine shop, or want to get running right away, this is a huge time and cost saver. The head adapter for the 6-inch EZ Flow allows for easy replacement of the head-bolt adapter plate and bore sleeve. This means you can quickly change your bench to flow different-style heads and engine bores in minutes.
The standard 4and 6-inch systems come with a head adapter and components to accommodate a small-block Chevy and small-block Ford bolt pattern with a 4.030-inch bore.
Other Bench Sources
After building my British Standards compliant monster bench and using it for several years, I moved from the UK to Tucson, Arizona. This was my second introduction to SuperFlow airflow benches. I had used a small 110 for accuracy comparison to my home-built bench while still living in the UK. But that was only a few hours of experience.
In 1976, the publisher I was writing for acquired an SF 300, which is the big bench that evolved into the SF 600. I have put literally thousands of hours on such a bench. I still, as of 2012, regularly use an SF 600 bench with all the Audie Technology addons. The only difference between what I do on this bench and what most others do is that I use a sliding scale of pressure drop, the same floating pressure drop I described earlier in this chapter.
Another bench I am cur-rently testing on is the Saenz J-600 bench, built in Brazil. What I can say is that this Saenz unit lends itself well to the floatingpressure-drop measurement technique because it pulls a lot of vacuum. Combine this with the fact it comes equipped with the Audie Technology flow measuring gear and software, and you get a bench that delivers results in a standard form while measuring with a sliding scale (floating) pressure drop—all good for doing the job right.
Written by David Vizard and Posted with Permission of CarTechBooks