| Author |
Message |
    
Elsee
| | Posted on Wednesday, March 26, 2003 - 6:24 pm: |       |
Can you tell me more about porting the swirl-port truck heads? |
Bogie
| | Posted on Monday, March 31, 2003 - 2:30 pm: | |
Yes give me a couple days to complete what I'm writting. |
Webmaster (Admin)
| | Posted on Monday, March 31, 2003 - 2:44 pm: | |
Hey Bogie, just remember, we have a limit to how much file space we have for our web site.
Just kidding.  |
Bogie
| | Posted on Tuesday, April 1, 2003 - 9:48 pm: | |
Little appreciated, swirl ports feature a similar combustion chamber design to the L-98. Now, if you own or have access to a die grinder, you can make these turkeys turn and burn pretty well. They will always fall short of Vortecs or Fast burns when it comes to ultimate power, as swirl ports and L98 heads just don’t have the high turbulence combustion chamber of latter descrided heads. But for sure, the swirl ports are considerably better than the SMOG heads that preceded them. So compared to the Vortec your always going to be short about 10 horses. Compared to Fast Burns about 20 because the aluminum material allows for greater compression. You can, however, make the Swirl Port deliver about 20 more ponies by porting and shaping the swirl vanes into the guide and port roof, thus allowing more top end flow with little or no loss of swirl anywhere in the rpm band.
Before you take a grinder to your swirl ports, you need to consider whether your time and money wouldn’t be better spent on a set of Vortecs, or say Iron Eagles. Only you can decide that, but for 500 to 600 bucks you have a head that will deliver more power, greater compression tolerance, and get better fuel economy than the modified swirl port. You don’t have the expense of tools and equipment to grind ports. You eliminate the potential of ruining the head by grinding through the water jacket. Further, you don’t spend money on a valve job and milling.
That being said let’s go, what I’m about to say about porting applies to all heads. It’s less, or not, effective with Vortecs and Fast Burns because the factory already did a great job with design and casting of these heads.
Before I get into porting (part 3), I want to discuss a little general theory and provide a some data in the hope of giving a bit of understanding of why combustion chambers and ports work the way they do (Part 1). I also want to discuss shop procedures and safety a little bit (Part 2) and then get into porting.
This input is only Part 1 the Introduction as I'm trying not to overwhelm the memory capacity of Sallee's server.
PART 1 the INTRODUCTION: What’s going on in the cylinder head
Please appriciate that I’m speaking in general form and cannot address every contingency and design nuance, as there simply isn’t space.
I know everybody keeps screaming port volume; I curse Jenkins and Yunick for this damn concept. While there's truth here, it's found mostly at the extreme end of the envelope. Like big displacement motors turning 8000 rpm with huge cams and bunches of gears. But lets face it; most of us are trying to get down the street with more efficiency and a bit quicker. We're not trying to win NHRA Summer Nationals with our pickup.
Actually the ideal port would be elastic, becoming smaller at low rpms and, of course, bigger at high rpm. Now there's a thought!
Much can be done to enhance port flow, without resorting to holes so big a 747 would stall out in the stagnant air. If you ever conducted a little test to find where the airflow goes; on the intake you'd see that most, by far, is concentrated on the 1/3rd to 1/2 of the valve facing the sparkplug wall toward the middle of the chamber. The stuff that flows on the 1/2 to 2/3rds of the valve facing the cylinder wall around through the short side port radius is pretty minor. The old 80/20 rule; in this case 20% of the valve is supplying 80% of the flow. You can test this for yourself. Get an old head with a soft spring retaining one chambers set of valves. Get a piece of wood a bit larger than the head. Line up the head and drill a few boltholes through the wood. Scribe and cut a cylinder hole large enough for a piece of 4 inch drain field pipe. Glue it into the wood. Get a 4 inch plastic plug and make a hole sized so you can plug-in the vacuum inlet of your shop vac. Go to the hobby shop and get a spray can of model paint, for the extremely fine pigment (water based is prefered unless you like fire streaming from you shop vac). Bolt the head onto the board with rhe cylinder adapter and fasten it to your workbench. Mold some clay around the inlet to smooth the boundary layer entering the port. Fire up the shop vac. Now shake the can with the water based spray paint, then with a ruler in hand to measure valve opening, press the intake down say .45 inch. With your free hand, shoot a little paint down the port. A couple fine mists are better than soaking the thing. Carefully close the valve and shut off the vacuum. Unbolt the head and remove the valve. Where's the paint trail, yep you guessed it, right where I said it would be. Don't perform this test on a hemi head or you'll go into depression. Then you'll want to build a hemi headed SBC for all the wrong reasons.
OK, so now you know where the air naturally wants to flow as it passes out the valve. I'll save you a step; don't try to make it go where it already doesn't. You'll make the damndest dead engine you've ever seen if you do this. I can't tell you how costly that lesson was. OK, so I learned it on a Ford FE block, but the knowledge transfers, trust me. I don't know how many hours of my youth I spent cutting classes so I could cut heads apart, building Plexiglas port models and hooking them up to a furnace fan powered flow bench (really clears the yard of small kids and pets). Then circulating smoke from cigarettes and old Lionel steam engine smoke units thru ports and models of ports. Or watching water flow around bends in a stream or passing around the street corner. The thing you see is that flow goes to the out side of the turn. On the inside, local flow is often reversed against the main flow’s direction. The sharper the bend or the faster the flow the more pronounced these affects are. I finally went crazy and began to attend college aerodynamics and fluid dynamics classes just to try and figure out what's going on. It's enough to drive you to early old age.
Intake airflow in a wedge headed engine wants to form a spiral flow along the perimeter of the cylinder. Some engineering texts refer to this as a tangent flow, I’m not sure that’s really a correct description, but we’ll live with it. The port needs to be designed to enhance this characteristic. The major flow exits the valve aimed at the spark plug. It forms a vortex that spirals down the cylinder as the piston descends toward Bottom Dead Center (BDC). A major advantage of the wedge chamber is that the intake valve is shrouded on the cylinder wall side. As the piston ascends toward Top Dead Center (TDC), while the valve is still open, the cylinder wall side of the combustion chamber helps to prevent the swirling flow arriving at the backside of the valve from throttling flow entering from the spark plug side.
Now that’s a heretical statement isn’t it, to say shrouding is good when everything you read says it’s bad, all of it. Read on and I’ll try to make some sense out how you can use shrouding to your benefit.
Contrast this to a hemi headed engine. On paper or on a uni-directional flow bench, like your vacuum, the hemi chamber appears to have it all over the wedge. The hemi utilizes 1/2 to 2/3s the circumference of the valve compared with 1/3 to 2/5s the circumference of the wedge head valve. So why doesn’t the hemi just run away from a wedge? The answer lies in the swirl pattern. The hemi’s swirl is vertical, that’s to say when the port is aimed straight on, as in the Chrysler, the principle flow pours around the valve, passing over the sparkplug and exhaust valve. It then floods down the far side of the cylinder wall chasing the piston as it descends toward BDC. All’s good so long as the piston continues on the down stroke, but as the piston rises on the compression stroke, the vertical orientation of the flow rises up the intake side of the cylinder wall and rushes back over the intake valve. Since the valve isn’t shrouded, the rising flow essentially throttles the incoming charge, slowing flow significantly before the valve closes. Therefore, the cylinder never fills as well as theory and flow benches would indicate.
Being an aficionado of cylinder head design, I’m always looking into what’s being used in various engines. I found an interesting design used by the Yamaha Virago/V-Star vee twin engine. The combustion chamber is a cross between a squish/quench wedge and hemi design. The valves sit in a traditional hemi form. The chamber is rotated such that the intake faces toward the center of the engine and the exhaust faces outboard. The spark plug enters into the top of the hemi chamber adjacent to the intake and exhaust valves. Opposite the spark plug and the valves is a heart shaped squish/quench deck, similar to what we see in contemporary high performance automotive heads. Never mind this design is about 25 years old now. This is also a very long rod motor at 6.5 inches against a 2.8 inch stroke, for you guys that care about such things. The intake port is off center to the valve such that it encourages a three dimensional swirl pattern that would be more similar to a wedge chamber in that it rotates around the periphery of the cylinder rather than down the cylinder in the traditional hemi scheme. Harley uses a somewhat simpler version of this in what’s called a “Bath tub Hemi” on the Evo and newer engines. Offenhouser used a circumferential quench belt around an otherwise conventional hemi chamber with a stepped dome piston. These things help invigorate the hemi chamber with otherwise lacking turbulence. This helps provide some mechanical octane and a more consistent burn cylinder-to-cylinder and cycle-to-cycle. Of course nothing beats a hemi chamber for producing power with high boost pressure and lots of nitro-methane, but we’re building street power, remember.
Where the contemporary heart shaped squish/quench deck and a relatively open combustion chamber originates from is a question I can’t answer. As previously stated, I’ve seen this configuration on the Yamaha Virago, albeit combined with a hemi rather than wedge chamber 25 years ago. The first time I saw this as a wedge chamber was on a Doug Roe modified Vega head back in the early 1970’s. Back then my partner and I were, among other things, were running an Offy powered midget. Becoming tired of “hold up prices” for Offy parts, we were searching for a substitute engine. Now many guys were running modified Chevy II 4 bangers and V-8s modified into inline 4 or V-4 configurations. All of these modified engines had reliability problems (read that, leaked water like sieves) such that you might just as well pay Offenhouser prices and enjoy the greater reliability. So when the Pinto and Vega OHC engines became available, I started cogitating. We settled on the Vega engine and picked up a couple junkyard dogs to build up. Year one’s design used TRW forged 11 to 1 pistons. These pistons included a T slot dome. The domes essentially provided a high squish/quench chamber that was otherwise missing from the Vega’s open chamber wedge design. This was accomplished through a heart shaped squish/quench dome opposite the spark plug and a pair of domes set adjacent to either side of the spark plug, thus forming the T-slot. This engine, however, suffered like other engines where the combustion chamber was built into the piston rather than the head. Examples are the 348/409 Chevy, 383, 410, 430, 461 FoMoCo (Edsel, Lincoln, Merc), or the Ford Cortina, and others. The issue seems to be that the engine’s efficiency and resistance to detonation is never what the arithmetic says it should be when the combustion chamber is contained in the piston. Year two, I discovered that Dog Roe was modifying Vega heads to include a high squish/quench combustion chamber. This heart shaped chamber of 30 years ago was the classic prototype of high efficiency chambers we see today. By employing this head and a flat top piston the efficiency (fuel burn versus horsepower) and resistance to detonation (mechanical octane) of our Vega engine became much closer to the computed numbers.
Studying what went on between the combustion chamber in the piston versus in the head showed that the effects of swirl and late compression turbulence differed considerably between the approaches to essentially the same combustion chamber configuration at TDC. The combination of the open chamber Vega head and the TRW T-slot piston created two problems with the induction swirl. The swirl died out from the aerodynamic resistance created by the domes protruding above the piston crown. And the swirl had access to the un-shrouded cylinder wall side of the intake valve. This returning flow essentially throttled inlet valve flow as the piston was commencing the compression stroke toward intake valve closure. And aerodynamic resistance from the domes damped what swirl was left from valve closure to TDC. The result of these events could not be overcome by the shot of turbulence created by the domes as the piston closed on TDC. The effect was like eliminating 15 to 25 degrees of post BDC cam timing. The softened turbulence caused unstable resistance to detonation cycle-to-cycle and cylinder-to-cylinder. To establish a more predictable situation, more fuel was used. The most obvious side of a richer fuel mixture is poor mileage, but on a racecar this is not of great importance unless your rule constrained to capacity and or a maximum number of pit stops for fuel. It does however affect top end lube as excess fuel washes the lube from the cylinder walls. This results in piston and wall galling and at the extreme, piston, ring, and pin seizures. Not to mention excessive heat in the exhaust system from post cycle combustion which may look impressive as flame shoots from the exhaust pipe, but this really restricts exhaust valve cooling. Installing Mr. Roe’s head offered improved late cycle shrouding of the inlet valve, thus allowing the swirl to continue without acting to throttle the incoming charge. Further improvement is seen where the domes are not damping swirl as the piston approaches TDC thus there is greater turbulence at ignition and greater power generated from the mixture. Since fuel is no longer being used to overcome inefficiencies and to provide detonation resistance through evaporative cooling, power went significantly up, galling and seizures went away, and exhaust temps went down and exhaust valve and pipe life went up.
Next time Shop Proceedure and Safety |
305MAN
| | Posted on Wednesday, April 2, 2003 - 11:06 pm: | |
Bogie, you got my attention: I'm using late-model swirl-port heads and domed pistons in my newest engine. Keep the information pouring........... |
Bogie
| | Posted on Wednesday, April 9, 2003 - 7:15 pm: | |
Shop Procedure and Safety
I meant to include some reading recommendation with the previous installment and forgot so here they are:
“How to build and modify Chevrolet Small Block V-8 cylinder Heads” by David Vizard and “Small Block Chevy Engine Build-Ups” by the editors of “Chevy High Performance” magazine, also, use their web site at http://www.chevyhiperformance.com/perfdir/ for tons of useful info.
Before I get to actually discussing grinding ports, I want to introduce the subjects of tools, techniques, and safety. Generally porting requires a die grinder powered by compressed air or electricity. Also, required is a selection of cutters, stones, sanding drums and buffers. You will need a sturdy workbench to support the head safely and maintain it in a comfortable working position for you. You, also, need protection from noise, vibration, temperature, and the cuttings.
Grinders:
A high-speed die grinder is a necessary tool to accomplish porting within a reasonable period of time. You could use an electric or air driven drill motor as a power source, but you’ll find the speed of the work will be tedious at best. Where-as, a high-speed die grinder greatly reduces the process time. You might want to consider having a Dremel Tool available. These “hobby” grinding tools are excellent for fine work. They get into tight places that die grinder can’t and are great for finish buffing and polishing. Choices of die grinders are those that are compressed air or electric powered. Both have their advantages and disadvantages. I use both types, but do most of my work with the electric grinder.
Electric die grinders are more expensive to purchase than air grinders. However, while the air driven grinder is quite inexpensive (20 dollars at Home Depot), it requires a pretty good compressor to run it. So if you don’t have a compressor, that cost needs to be figured in to the equation. But the purchase of a compressor also supports many other tools such as air wrenches, spray-painting, cleaning & drying of parts, etc. so there's justification to have a compressor in the shop. When purchasing a compressor, its output in Cubic Feet per Minute (CFM) at a specified pressure needs to match the tool's requirements. This issue is larger than just reading the CFM specs of the compressors and tools, you run into “Duty Cycle” of the compressor. Porting requires that the grinder run continuously for extended periods of time. This taxes the compressors “Duty Cycle” which is the period of time it can be continuously operated. Small compressors, especially the oil-less type with 30 gallons or less of tank capacity will be pushed to their limits by a die grinder running for hours at a time. When constantly running, my air grinder will trip the switch on my Ingersoll 8 hp, 2-stage compressor with 80-gallon tank about every minute and a half. The same grinder hooked to a 5 hp, single stage, oil-less, 20-gallon Craftsman compressor trips the on switch every 15 to 20 seconds. So the small Craftsman essentially has to run continuously to supply the die grinder. This is not to say a small compressor won’t work, but you’ll use a lot of its life up doing this job. If you’re inclined in the direction of air tools, I recommend that you give serious consideration to a large compressor possibly a 2 stage, certainly one with a 60 to 80 gallon tank. I find it more fatiguing to use the air driven die grinder for extended periods of time compared to the electric grinder. The exhaust air is very noisy and depending on where the exhaust air exits it may chill your hand, soak you or the project with exhaust oil, and potentially blast cuttings and dross all over the place. Additionally, the air-hose is relatively heavy and is always pulling on your hand, which makes delicate control more difficult and fatigues your strength. This is not to say air grinders are not useful or effective, they are. If you don’t already own one, I’m pointing out some of their more negative qualities.
30 years ago I purchased a Sears electric die grinder. It has a long snout that lets you get into tight areas. It has proven to be extremely rugged and through the years has out survived 4 or 5 sets of brushes. I’d say I’ve gotten my money’s worth from it. Like air driven grinders, the electric is noisy and vibrates so ear and hand protection is required. The electric cord being lighter and more flexible than an air-hose makes the tool easier to guide and less fatiguing to use for long periods of time. The real negative is that the motor becomes quite warm to the touch and is heavy compared to an air driven grinder, which reintroduces some of the fatigue factor.
Stones and Cutters:
My preference has usually been to use grinding stones. They’re cheap to purchase (but you'll need a lot of them so I guess the cost agaist carbide cutters balances out) compared to quality cutters. Since a stone wears away, they develop a multitude of shapes and sizes as you use them, which is useful in different locations of the port. I’ve done this so many times I a have a rhythm. I start in the same place every time and proceed to a plan that allows the stone to wear into the shape and size I need as I cut through my porting sequence. This minimizes having to stop and change cutters thus speeding this rather laborious task. Stones also offer the advantage of being easy to clean and reshape using the stone-dressing tool made for that purpose. If you’re cutting aluminum, this feature is very important, as aluminum fouls the stone (or cutter); therefore, having the ability to ”kiss” the stone against the tool quickly cleans it. The stone I find most useful for porting is the ½ x 2-inch high-speed stone from Sears. For safety, you must match the stone to the grinder’s speed. Die grinders are high-speed tools turning 10 to 30 thousand RPM. A low speed stone will disintegrate at high RPMs presenting you with a considerable injury hazard and could result in loss of grinder control damaging it, you, and your cylinder head. I use a fresh stone for each port, so use that as a guide to plan how many to purchase. I must say, however, that a high quality long shank carbide cutter really helps in getting to those deep cuts, so even if you opt for stones, you’ll need at least a couple long shank cutters as well. Purchase ball or oval shaped cutters, unless you really building super high performance racing ports, you will have no need for sharp edged, rectangular shaped cutters.
Aluminum can be a real pain to cut with either a stone or a cutter. It melts at temperatures being generated at the point of contact and clogs the cutting surface of the tool. You can clean aluminum from a stone with the previously mentioned dressing tool. A cutter is more difficult to clean, this requires running the cutter against a piece of steel or iron, and/or using a sharp knife blade to cut the aluminum from the teeth, either of which is pretty time consuming. However, there is a very helpful trick. If you run the stone or the cutter against a bar of hard soap when you start the cut and repeat every couple minutes, you'll find the incidence of aluminum fouling almost goes away. I use Ivory because it doesn’t have much of a smell, but any old hard style bar soap will do. It’s worth noting that there’s a difference in cutters designed for aluminum or iron/steel, try to match the cutter design to the material as the work will go much faster, especially if you don’t use the soap trick.
When purchasing cutters, you’ve got to step up to the cost of carbide. The sharpness of tool steel simply goes away at these high speeds when used on relatively hard (compared to wood or plastic) materials like iron or aluminum. You’ll spend a fortune and loose considerable time replacing ordinary tool steel cutters. Carbide provides many times the life compared to tool steel. They’re expensive and of course you can’t reshape them, like you can a stone, so you need to by several different styles and sizes to accomplish the porting effort. Summit, Jegs, Competition, maybe even Sallee, to name a few, sell porting cutters with different selections of shape, diameter and length. They are available in configurations for iron and steel, as well as aluminum. As previously stated, matching the cutter pattern to the material reduces work time and in the case of aluminum, reduces the clogging issue, but keep that bar of soap handy if your cutting aluminum.
Polishing:
Polishing can be accomplished using the die grinder with sanding and buffing accessories (mandrels, sanding drums and buffing pads) made for that purpose. But for this finer work I find the die grinder to be rather cumbersome. With the exception of doing some rough in polishing with the die grinder, I find this is where the Dremel type tool excels. However, with the possible exception of the combustion chamber and the backside of the valves, we’re not polishing anything.
Safety and Comfort:
Porting is an icky activity at best. It creates an environment of high noise and vibration, uncomfortable temperatures and fatigue. There is the ever-present risk of cuts, eye and hearing damage, and other injuries that include those to your lungs due to inhaling cuttings and dust.
Porting is an endurance activity; you’ll be at it for hours at a time. So you need to be comfortable as possible. To start with you need a sturdy workstation. This can be a workbench, or in some cases engine stands are used to secure the head. What ever you use, the head must be solidly retained so it doesn’t fall on you. A fall risks considerable damage to you, bystanders, and the head. You will need good lighting in the port to see where you’re cutting. A system to vacuum the cutting debris out of the port is highly desirable. Whether you sit or stand is a choice you need to consider in designing your workstation. Lastly since you’re probably in the garage or some other miserable place, you need to consider heating or cooling so you remain comfortable. Like I said, porting is an endurance activity, the more comfortable you are, the longer you’ll last, the better will be the job and it’s safer for you. Plan to take frequent breaks and keep plenty of refreshments and snacks close by. I’m a chip and soda guy, but whatever you like, don’t drink alcoholic beverages till you rdone for the day. The risks of even a minor screw up turning to disaster with these high-speed tools are enormous.
Die grinders operate at high speeds with all the attentive noise and vibration you can expect from those speeds. First and foremost is the requirement to protect your eyes. As previously stated, cutting stones can disintegrate casting anything from large chunks to small high-speed particles in any direction. So your face and eyes are subject to and need protection from these impacts. All of this stuff is bad, especially, in the eyes and needs to be stopped. A good face shield and/or tight fitting safety glasses are a must. Good quality ear protection is necessary to isolate you from the high pitch sound. If you don’t protect your ears, you will find that the sound of the grinder will remain with you for hours after you stop work. This is a clear sign that damage is being done to your hearing. Since you’ll be at these ports awhile, probably several evenings, the cumulative affects can be quite harmful. So you can take you choice, loose your hearing to the die grinder or loud Rock and Roll. Lastly, the vibration is especially tiring to your hands; it’s not uncommon to have your hands feel the vibration for hours after you stop work. This, also, is sign that nerve damage is occurring. You need to isolate yourself from the grinder with a good set of mechanics gloves. Gloves also provide protection from the hot electric grinder, or the cold oily exhaust of the air operated grinder. Again this improves your endurance for the long haul of this job and helps you to meet the quality requirements this effort demands. I’m sharing these concerns of safety from first hand experience. Having ignored these things in my younger years, I have, and it worsens with age, constant ringing in my ears and really bad carpel tunnel syndrome in my right had, it always has a distant and buzzing feeling like it’s not really attached to you but has a machine like a die grinder running in it’s grasp. It hurts all the time, and falls “asleep” when riding my Hog or doing anything that requires grasping where little or no relief from the finger tension can be had for lengthy periods of time. So for the cost of some shop gloves and earplugs, you can avoid all that misery, so like the God Father says “… DO IT!”
The grinding process results in a lot of grit. This will be a mixture of the metal filings; combustion by-products if it’s a used head (even a clean one), stone grit, and/or microscopic amounts of carbide from a cutter. This stuff is very invasive to your skin, eyes and lungs and will do great damage, particularly to eyes and lungs. In the lung, at the extreme, this stuff could result in cancer, so you must take precautions not to breath the cuttings. A very effective defense is a breathing filter. The cheap white masks are considerably better than nothing, but a nice face fitting rubber mask with the twin filters on each side is a tremendous improvement.
Most of the grit can be eliminated, by using a shop vacuum to remove the cuttings as they appear in the port. You also need good illumination into the port so you can see what your doing. Take one of those aluminum light reflectors (we’re at Home Depot again) and modify it so it can be fastened to a board. Make a hole in the reflector large enough for a piece of tubing that can attach to your shop vacuum’s hose. Take the board and make a hole large enough to allow it to be centered over intake or exhaust ports, or the combustion chamber as each is worked with the grinder. This might take 2 or 3 boards/adapters to solve the matching requirements. Into the board/adapter drill a set of holes that allow it to be fastened over each port or combustion chamber in turn as they are worked using at least 2 bolts that secure the adapter to the head. This will provide a secure source of working light and a vacuum connection to remove the cuttings from the work zone.
Next time we’ll get into porting. Meanwhile, go get the books I recommended and read them. You’ll find in my next installment that I have my own variations, opinions and test data that I will share with you. In some instances I don’t agree with the published processes or results and I will tell you where and why (my secrets) but those books provide much more detail than is possible to do here, besides they have pictures and charts which help you visualize what the words are attempting to convey. |
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