Granted, this chapter is titled “Porting Tools, Consumables and Safety,” but I address the safety issues first because it is vitally important you understand just how critical they are.
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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Eye and Lung Safety
Make no mistake about it—an 18,000-rpm die grinder with a carbide cutting metal is a nasty little predatory critter spitting out fine, razor-sharp shrapnel. It’s not just the very sharp shards of metal, but that they also come off the work piece at speeds up to 60 ft/sec. If they hit you, the end on these razor-sharp shards will, with ease, penetrate your eye up to 1/16 inch deep. That means a “right now” trip to the hospital for some painful eye care. So get a good set of safety glasses, the type that wraps around, so that ricocheting shards don’t get into your eyes from the side.
With your eyes taken care of, it’s time to consider your lungs. Do not, for any reason, use abrasives without first putting on a mask. You don’t need to do that many times before lung damage (usually silicosis) goes from a possibility to a certainty. I can be very categorical here because I found out the hard way!
Using a shop vac to keep the work area clean is also a very good idea. Sticking the end of a shop vac into the open end of the port you are working on not only helps keep your shop a whole lot cleaner but it also allows you to see what you are doing in the port while it keeps it clear of 99 percent of the cutter/emery-roll debris.
Grinders—Air or Electric
Other than the components we are going to port for more airflow, there are many aspects of an engine that can be improved with the aid of a die grinder, some carbide cutters, and a box of emery rolls. If you are just starting out, you need to consider the pros and cons of the two most popular types of die grinders: air and electric. Air grinders are cheaper, if you already have a compressed-air source. Consider 4 scfm at 90 psi a minimum with 5 to 6 scfm as a good working capacity compressor for just about all the regular types of die grinders.
The compressor takes your main cash outlay for an air-powered porting system. After that, there are some low-cost options open to you in terms of air die grinders. There are many discount tool outlets that sell cheap die grinders costing as little as $18. They are of lower quality than grinders costing $50 or more, but there is a fix. If you use the BND Automotive air tool oil as I do, the cheapo grinder’s life is extended about tenfold. That gives them about the same life porting heads as a grinder costing three to five times as much.
Electric grinders are a little more costly and there are a few underpowered models you should avoid. For instance, don’t buy a model-maker’s grinder; it’s grossly underpowered for the intended task. If you intend to get an electric grinder, it needs to have at least 1/4 hp but preferably 1/2. For speed, you require about 20,000 rpm max.
Again, electric grinders cost a lot more but tend to be of better quality. Also consider that they are more bulky, which can make using one more tiring over a day’s grinding. The preference of many cylinder head specialists I come into contact with seems about split down the middle. My position is: For home-based porting you need air. After what my friends jokingly called my retirement, I built a shop in the basement of my house. I had to have a compressor for a multitude of other jobs, so air die grinders made a lot of sense.
If you bought the right die grinder, it should be capable of 15,000-plus rpm. But some jobs call for a lot less, so a speed controller of some sort is needed. For an air grinder the solution is a simple pressure regulator. Many compressors have one as a matter of course. Regulating this to 30 or so psi slows a typical air grinder to about 2,000 to 3,000 rpm, a speed ideal for finishing intake ports with a relatively coarse emery roll. Many hand-held electric die grinders are in the 500to 600watt range, so you can use an SCR dimmer light switch as a cheap and effective speed controller. This type of switch can be rated at 600 watts or more and is up to this job.
The only type of cutter that removes metal and lasts is of tungsten carbide. Do not consider any other type. For cast-iron heads, a fine-tooth cutter removes metal faster and produces a finer finish. For aluminum, the tooth form needs to be coarser to minimize clogging during use. For what it’s worth, you can spray WD-40 onto whatever aluminum part you are reworking, and it almost eliminates clogging. The best anti-clog/finish-enhancing lube is supplied in the porting kit sold by Dr. J’s Performance.
For most porting jobs you need only have the cutter forms and shank lengths shown in Figure 6.8.
Support Porting Tools
At this point, you should be up to speed with whatever metal-removal tools are needed to get you started. Next, we look at tools that physically aid the production of shapes that best meet the goals of airflow and port efficiency and for achieving the best sizing to maintain good port velocity.
Dr. Air’s E-Bar
Although this book covers porting in general, for two-, three-, four, or five-valve heads, it’s a fair bet that most of you are porting something with a pushrod hole running right up past the side of a port. Here, I am referring to such heads as small and big-block Chevy, Ford, Chrysler V-8s, and the like. If that’s the case, you have to widen the port at the pushrod pinch point. The problem here is quickly gauging just how much metal there is left before breaking into the area where the pushrod passes through. If you do break through unintentionally, it can be welded closed but that’s an inconvenience to avoid. To get the port width to a maximum without breaking through, and in a fast, efficient manner, I strongly recommend using Roger Helgesen’s E-Bar tool.
Tagging the Flow
To successfully port any head or manifold, you need to know about two aspects of the flow: where flow is most restricted and the direction it is flowing at any particular point. The easiest way to establish the general direction of the flow is to use strands of cotton epoxied onto a piece of welding rod. While you are making one of these, you may as well go ahead and make three: one with 1/2-inch-long strands of cotton, one with 1-inchers, and one with 1½ inchers.
Inserting these into the port indicates the general direction of the flow at any particular point. Now, it may seem like I am being a little vague here about this technique for ascertaining the flow direction. That is indeed the case and for good reason. The flow is turbulent at any port velocity that exists in a running engine (I address port turbulence in Chapter 10). Depending on the size of the vortices, the cotton strands vibrate, leaving you to make an estimation of the general flow direction that is taking place at the point of interest.
As simple as it sounds, a suitable long screwdriver with a tip about 3/8inch wide can be a handy tool for investigating the short-side turn of any port that has a downdraft angle of less than about 30 degrees and/ or a tight short-side turn radius. Get one and place it somewhere handy.
Knowing how fast the air is going at any point is probably going to tell you in which direction it is going. Probing a port to determine speed at any given point can be very informative. Like most things, there is a good and bad way of doing it and a cheap or expensive way of making the measurements. The more costly way of making the measurements is probably the most common and not necessarily the best. The usual tool for port probing is the Pitot (pronounced Pete-Oh) tube named after Henri Pitot, who resided mostly in France during the 1700s. Pitot tubes are commonly used for airspeed indicators in aircraft. They do this by referencing the stagnation pressure, due to head-on motion into one orifice, and referencing it against the ambient or static pressure as measured from a second orifice.
With a little calibration and some math, we end up with the air speed in the port. You can source Pitot tubes suitable for this use from Performance Trends but the reality is that they are far from essential. In the past, I used regular Pitot tubes, but they can be cumbersome in the confines of a curved port and are sensitive to yaw. A few degrees of misalignment with the flow, and the measurements are wrong. About 1985, I adopted the far simpler and significantly cheaper method Roger Helgesen showed me. This simple method employs a length of hose with a piece of welding rod inserted into it.
One end of the hose is connected to a manometer, and the other end is located in the port at the point where you wish to establish the velocity. The purpose of the welding rod in the business end of the hose is to give it some rigidity to allow you to probe around corners. Do this by bending the welding rod and hose to a suitable shape to explore areas not accessible by a regular Pitot tube. By suitably bending and making handheld adjustments within the port, you can position the end of the test tube so it is aligned along the direction of flow, giving a more meaningful reading. To make this test probe easier to use, put a loop in the hose (and the welding rod inside it) so that everything stays in place.
Although this probe is far easier to use and costs almost nothing, the reasonably consistent results do not fully agree with those of a regular Pitot tube. To get a good idea of the port velocity, Figure 6.17 is the graph I generated to calibrate a device such as this.
At the other end of the scale, we have Laser Doppler Anemometers. I was first introduced to these in the 1990s when a salesperson came into my shop in California and tried to convince me I needed one. He told me that he had just sold one to Cosworth. The salesman said that he could sell me the same model as Cosworth’s at a whopping $440,000! I said I felt it best to pass on that offer.
What is a Laser Doppler Anemometer? Basically, it is a device for unobtrusively measuring the velocity of a transparent medium. A laser beam is first split into two beams, which are then both focused on the point of interest. Where these beams intersect, a moiré effect (light and dark bands) is created. As particles pass through this area, their reflectivity fluctuates. By measuring the rate of particle fluctuation, velocity can be determined. As good as this sounds, it still takes a fair amount of time to do a complete 3-D velocity plot of a port. Worse, you could only plot where there was a straight line of site to the area of interest. A better bet for investigating velocities within a port is by computational fluid dynamics (CFD).
This exciting subject is coming of age for the serious head porter and is something I delve into in Chapter 10.
Swirl and Tumble
There are many standards used throughout the industry for swirl; so unless you are using the same system as someone else, comparisons are not that readily done. There are several ways that I am aware of and have used to determine charge motion, whether it’s swirl or tumble. Torque is where a strain gauge is located at the center of the bore and has torque applied to it by means of a honeycomb. The greater the swirl, the higher the torque exerted. This type of swirl meter is rare and I do not know of any company currently offering it.
The RPM swirl meter is probably the most common. Performance Trends and Audie Technology make these meters. The Performance Trends unit is a paddle-wheel-style instrument and requires a simple paddle wheel be made for each bore size that is to be used for the test.
Seat Flow Distribution
It is very useful to know where the air is exiting the port (intake) or the chamber (exhaust). Like many others, I made up valves that had a small hole in the seat that then communicated to a hole up the stem. From here a manometer was connected and by observing the pressure drop at a given lift around the whole circumference of the seat, a good idea of the flow pattern could be established. A fancy tool to do just this is made by RTS Tooling. This method (though a little more costly if you buy one or more time intensive if you make one yourself) is very effective and delivers a wealth of data very rapidly. The RTS setup comes complete with a computer program that does 99 percent of the number crunching for you. It also produces a situational chart for each lift value investigated, to show where the air is flowing. My system for showing the flow is a little different from the RTS system and is shown in the nearby test done with an RTS setup on a big-block Chevy head (Figure 6.27).
Another way to do this kind of test is to set up your shop vac to blow air into the intake port and test from the cylinder side. For a test like this, it is the flow patterns that are being investigated, so it is not necessary to measure the CFM during the same test. If you are clever about it, you can create a system that allows chamber de-shrouding to be optimized without actually taking the head off the porting bench. All you need is to have a couple of valves that can be preset to a given lift. If the system is coupled to a manometer, you have a floating test pressure bench that actually resides on the grinding bench.
To establish where the flow is going, use the velocity probe around the valve. This works very well for the specific job of optimal valve de-shrouding. If you can’t afford CFD, this is the next best thing for chambers.
Sourcing Consumable Supplies
You can get carbide cutters, emery rolls, and the like from almost any tool and machine outlet that supplies regular engineering machine shops. If you live in or near any sizable community, there is likely to be at least one such outlet. The problem with buying at such places is they tend to charge much more than some other sources. Auto swap meets are a much less costly source for die grinder supplies.
If you can wait for one of these swap meets to be held nearby, you are likely to get your porting supplies at 30 to 50 percent less than from a typical machine shop supplier. This is all well and good, but you have to know what you are looking for and have the time to go get it. I know exactly what I am looking for, but an extremely busy schedule often prohibits driving 50 miles to get such supplies. For that and other pertinent reasons, I deal exclusively with Dr. J’s Performance. This is where Dr. J’s Performance and my good friend Roger “Dr. Air” Helgesen teamed up. Over the years, Roger has worked with several carbide cutter manufacturers to develop tooth forms that provide specific advantages for the head porter. The carbides remove metal faster and leave a better finish due to, among other things, a reduced tendency to bounce. These cutters can be had at prices that equal or beat swap-meet prices.
For the most part, only two forms of porting abrasives are needed for effective porting. These are emery rolls, or cartridges as they are some-times called, and emery disks. The rolls cover the work that needs to be done on the ports and the walls of the chamber, while the discs (usually on a right-angle grinder) are best used for the floor of combustion chambers. If you want to refine what you are doing, emery flap wheels of various sizes can speed up smoothing the short-side turns and the like.
For the best all-around results, go for coarser grits than you might at first suspect you need.
Since shape is far more important than finish, it is best to use a coarse enough grit to actually reshape the metal in a reasonably rapid fashion. The 80or even 60-grit rolls and the 80to 100-grit discs are about the best. Initially, these coarser grades remove metal fairly fast, making them ideal to carry on where the cutter work left off. After some use, they wear and cut as if they are a finer grade; so they are able to produce a finish appropriate to the job at hand. If the work is on the intake port, I usually use an 80-grit roll in new condition and finish the port at a slow tool speed. Here, about 2,000 rpm gets the job done. This method delivers a constant finish for good appearance, while still being a coarse enough surface to counter the forming of fuel rivulets.
Written by David Vizard and Posted with Permission of CarTechBooks