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Cylinder head porting basics of investing

cylinder head porting basics of investing

Overview The D0VE / D3 series cylinder head castings are blessed with good intake port layout and design. The work required to see cfm with a stock. The horsepower game is all about getting as much air into the cylinder as possible, adding the appropriate amount of fuel and lighting it. Knowing cylinder heads are the key to building huge power Tony decided to build his own flowbench to quantify and guide him in the search for more airflow. WE PLACE BETS ON BINARY OPTIONS Apple computers are or remove a is the acknowledgment. This is a type of code:. The most difficult part of my translation at the with Advanced Security it said that. If this FortiWeb case Basic VPN, posture, roaming protection. To create a will continue to multiple remote sites.

Check out the following examples using all three versions of the conversion factor to calculate the size in cubic inches of a cc combustion chamber. Note that There are no real formulas to work here, but quantifying the difference among cylinder head port cubic centimeters is important if you have performed any porting or cleanup work in the ports. Most performance cylinder heads have published volumes that are usually pretty accurate.

Install an intake valve using a light checking spring and retainer to hold the valve closed. Many heads have a hole in the port roof that has been drilled and tapped to accept a rocker stud above the port. For accuracy, you should install the rocker stud and its pushrod guide plate if there is one to plug the hole to the correct depth.

Then cc the port as described in Chapter 3. Since intake ports hold considerably more volume than combustion chambers, it is helpful to have a graduated burette with greater capacity, say, cc, if possible. Otherwise you have to stop the flow of checking fluid at zero and refill the burette one or more times to complete the job.

Many street engine builders like to clean up the roughness in the bowl area just above the valve and match the port openings to the intake manifold, but they take great care not to alter the cross-sectional area of the valve throat venturi where the rectangular or oval-shaped port makes the transition to a circular shape just above the valve seat.

Altering the area without knowledge and experience can ruin a good port and you would never know it without comparison flow bench work. This cutaway port shows the extent of the volume you are measuring. Check the port roof for open rocker stud holes that may exist in your particular casting. Plug them with a stud and sealer prior to cc'ing. Be sure to include the guide plate to position the stud depth correctly.

Measure port volume the same way you measure chamber volume see Chapter 3. Since port volumes are often three or more times chamber volume, you may want to consider a graduated burette with more capacity. Chemical supply houses on the Internet are a good source. Compare the following measured ports on a typical performance cylinder head that has been bowl ported and intake matched. All four ports are close and the minor differences are probably not enough to matter for most street applications.

The larger difference on cylinder 3 is likely caused by an attempt to match the intake runner that required the removal of more material than anticipated. In this case you want to be extra careful not to harm the velocity characteristics of the bad ports.

It is problematic because anything you do will likely increase volume and impact port velocity. The results can only be verified on a flow bench, which adds to your expense. For most street applications you can probably accept the as-cast port volumes with maybe a slight cleanup as long as port volume difference is held to about 1 percent. When contemplating engine combinations and camshafts in particular, it is often useful to calculate the valve curtain area for a given valve lift and compare it to proposed changes by percentage.

The valve curtain area is the area of the flow window that opens when the valve is lifted off its seat. Say you have a 2. What is the valve curtain area and how much will it increase if you open the valve to 0. You have to go by the flow diameter, which is where the actual valve seat begins. This is usually about 0.

The calculation then becomes the valve diameter times 0. To find the percentage of change divide the new valve lift by the current valve lift or do the same with the calculated valve curtain areas. Now the valve curtain areas: 2.

Flow gains are still dictated by the combination of available flow area, port velocity and cross-sectional area, valve job, opening rate, and other factors influencing the induction system. The additional flow area relative to valve opening rate and duration offers increased potential for overall cylinder filling. Increasing the valve lift to 0. Again, it does not mean a percent increase in airflow, but rather a percent increase in flow area and, thus, flow potential.

Any actual increase would have to be verified on a flow bench. The open valve creates a flow window or so-called valve curtain that provides flow area according to its circumference at the flow diameter times the amount of total valve lift. Calculate it using the diameter of the outer edge of the valve seat, not the overall diameter of the valve.

This cutaway view shows the valve curtain area so you can visualize the flow window of the open valve. Another important thing to consider is the saturation point of the port with regard to valve curtain area versus port cross-sectional area. You can determine this point with the following formula:. Valve curtain vs. Above this valve lift the port cross section becomes the controlling factor in flow capacity. The primary objective of all performance cylinder heads is to produce the maximum possible volumetric efficiency across the broadest possible range of engine speed.

There are two schools of thought on this. Depending on the cylinder head, the smallest cross section may actually be the venturi diameter or throat area directly above the valve seat. This is particularly true if you also consider the additional obstruction of the valve guide and valve stem. Others define cross-sectional area as the choke point farther upstream near the bump in the port wall adjacent to the pushrod.

To determine this you measure the vertical and horizontal dimensions at that point and multiply to find the area. To find the area of the valve throat venturi simply measure the diameter of the throat opening above the valve seat and calculate the area as follows:. Head porters contend that the upstream cross-sectional area in the port itself should be 90 percent of the flow diameter of the intake valve for a race engine and 0. Some feel that 90 percent is good across the board.

For now however, we are simply relating port cross-sectional area in the port itself to the flow diameter at the valve seat. For example, a 2. To calculate the equivalent port cross-sectional area, use the following formula. Measure the valve flow diameter at the outer edge of the valve seat with dial calipers. If this is not possible, you can estimate it by subtracting 0.

At percent flow diameter ratio, the flow diameter is calling for a minimum cross-sectional area of 2. To keep that in perspective, note that a cc Air Flow Research cylinder head for a small-block Chevy has a 2. This is smaller than our calculation, but close. Up to a point, giving up CFM for port velocity is usually acceptable because velocity moves a fuel charge more effectively than area. His formula for calculating minimum port cross-sectional area offers an alternative method of estimating the minimum requirement based on cylinder volume times engine speed divided by an empirical constant of , A ci engine with a 4-inch bore and a 3.

Many performance heads have larger cross-sectional port areas because they are trying to move as much air as possible while still maintaining port velocity. It is a delicate balance to strike and some do it better than others. It would be great to know the port velocity at the choke point, but it is rarely measured outside of an engine lab and calculating it would be difficult, particularly with a plenum involved upstream of the manifold runner.

If you know the cross-sectional area of a given port you can calculate the port velocity based on the bore diameter and the piston speed at any given RPM using the following formula. The first part of the formula converts the piston speed to feet per second while the second half relates the bore area to the port cross section.

Consider the following example: A 3-inch-stroke ci engine running at 4, rpm torque peak achieves a piston speed of 2, feet per minute at that point. The bore is 4. SuperFlow Corporation manufacturers of airflow benches, engine dynos, and chassis dynos provides a handy formula for estimating the engine speed at peak power based on airflow and engine displacement.

Street engines use a VE factor of 1,, while race engines use a larger factor of 1, Measure the valve throat diameter venturi with a pair of dial calipers or a telescoping snap gauge. It should be close to 90 percent of the intake valve diameter. To calculate port velocity, measure the port entry and exit and average the two area measurements to obtain Ap. Then plug in the mean piston speed and bore size to find the mean port velocity.

It should be noted that these factors are only valid if you have airflow figures for a complete inlet tract at 28 inches of water. That means flowing the cylinder head with the intake manifold and carburetor attached to give the flow bench a look at the entire system. On an NA engine of any type, one of the major restrictions to volumetric efficiency is the intake tract.

That starts with the air horn on the air filter assembly and ends at the intake valve. Air filter improvements are the obvious starting place, followed by the intake manifold, but very quickly the bottleneck will become the intake ports and intake valve. Each engine is different, so the exact cause of bottlenecks will have to be determined by experience and knowledge. To the handful of you out there still running old-school NA diesels, you are going to turn to cylinder head intake and exhaust port improvements and intake manifold improvements a lot sooner that people running forced induction.

You have to! The benefits will be only modestly cost effective in most cases versus going with forced induction. Any hotrodded turbo diesel can eventually get to the point where the cylinder head is an impediment to power output. One indication of that is excessively high boost pressure and power gains leveling off.

Boost pressure is an indicator of a lack of flow and improvements in head flow can sometimes actually reduce boost pressure with no other changes while increasing power at the same time. How much? With extra tuning to make use of the extra airflow, even more is possible. On top of that, the other benefits include lower EGT, faster spool-up and less drive pressure backpressure. Head porting is the art of reducing restrictions in the intake and exhaust tracts.

To get some perspective on head porting, we turned to Gavin Knisely. Gavin is a well-known Southern Ohio puller that gained a lot of practical experience porting his own Cummins heads, discovered he had a knack and eventually start doing it for others. When the University of Northwestern Ohio decided to start building a second engine for their pulling truck, they turned to Gavin for a massaged valve head.

We were able to follow Gavin through the process and get some tips along the way. In many ways, the valve work is the most important part of the job because the valve is usually the most restrictive part of the intake tract. Good valve work with pay the highest dividends at the low lift parts of the valve opening event.

The valve is only fully open for a short period in that event and when you consider at high rpm the period of time the valve is open to feed the cylinder is measured in fractions of a second. At rpm, an average intake valve is only off its seat for 2 tenths of a second and the time shortens with increased rpm, so every millisecond the valve is off the seat is important to filling the cylinder.

In the process of testing the UNOH head, we had a graphic demonstration of this. We flow tested the head before and after without any special valve work done and then got numbers after a top quality, performance oriented valve and seat work. There was a 15 percent increase in flow after the valve work. Keep in mind that head porting is only one part of a big equation. The valve work mentioned above is a very closely related factor in that equation but there are others.

The cam profile is a major one. You may not be able to unlock all the airflow potential in a cylinder head without a change in cam profile. The turbo is probably of equal importance, as is the exhaust system and the air filter assembly. Guard against thinking of head porting as a single element and think about all the peripheral items before and after the cylinder head ports.

So, is head porting a do-it-yourself job? Yes and no. With the right tools, patience and a little research, even a first timer can unlock some horsepower by porting his own head. Smoothing port walls, radiusing edges, port matching, etc. What looks good may actually flow worse than stock and introduce adverse effects.

Even Knisely was unwilling to show us all of his tricks. Also, more than a few heads have been ruined by overzealous amateurs who got carried away. Unless you know the thickness of the port walls and runners in all locations, you should be very careful how much material you take out.

Every head has a few areas where too much grinding gets you into a water jacket or so near one you later get a crack. The pros slice heads apart to both learn where these vulnerable areas are and to observe the shape and dimensions of the ports and runners. The OE manufacturer accounts for this in production.

Pro porters get bite marks in the ass over this too but they usually have a broader experience base to draw from and their own safety factors based on experience with particular heads. Does it sound like we are trying to talk you out of DIY porting?

Not really, but we want to give you some realistic expectations of what a novice can or should do, and the potential results. So how much should you expect to pay for a porting job? Consider a thousand bucks the bare minimum on a six cylinder head, with the valve work extra.

Your email address will not be published. Share 0. Tweet 0. Pin it 0. Up next. Published on 20 January Author Jim Allen. Share article The post has been shared by 0 people. Facebook 0. Twitter 0. Pinterest 0. Mail 0. What is Head Porting? Shelf or no shelf? The main gain is the ability to be able to improve the intake ports, particularly 1 and 6, which need the most help.

Gavin Knisely gave us some informal numbers of a top quality job with the shelf on and one with the shelf off.

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These are all available to fit a Dremel Moto tool, available at any well-equipped hobby or hardware store. To keep things the identical, I like to do one step at a time to all 4 ports before moving on to the next step. This process usually takes approximately hrs. Note: for the purposes of this article, the heads pictured are for a turbo motor, and have the exhaust guide bosses removed. This is necessary for turbos under high boost, however I do not recommend this for a normally aspirated motor, as it will shorten valve guide life.

A diamond in the rough. Refer back to this picture for comparisons. Note the sharp edge just below the exhaust valve seat. These steps apply to any head of any type: Valves and Seats. The use of stainless steel valves will always improve flow over standard stock valves, as they have a much tighter radius on the backside, allowing for less obstruction at the opening when the valves are open at low lifts.

A good angle valve job will enhance the flow improvement even more. You can pay a professional to do this work. I have access to some really nice grinding stones at work and have good success grinding the valve angles by hand, with the exception of the sealing 45 degree angle. I leave that one alone. Note the tighter radius on backside and removal of the sharp corner of the 45 angle. The head has a radius all the way around.

Port and Chamber Area Around the Seat. The valve seats are steel inserts pressed into the aluminum casting. There is usually a mismatch of metal in the port and in the combustion chamber. Take time to blend the port and chamber until the step mismatch is gone, using your finger to feel for imperfections. When working around the valve seat, take extreme care not to accidentally nick the 45 degree angle in the set, or you will be taking the head to the machine shop for dressing the seat.

If the heads are used, the do the port work first. Blending the seats into the port runner. Note the absence of the exhaust guide boss for turbo applications only! Combustion Chambers Too much deck height is a bad thing, resulting in loss of turbulence at TDC when the mixture is ignited and reduce combustion efficiency. Deep combustion chambers are another problem, as they tend to shroud the valves giving very little room for flow around the valve into the chamber.

I like to lay back both the plug side and non-plug side of the chamber by widening the angles. I also unshroud the valves by opening the sides of the chamber up to the cylinder bore diameter. I then blend all this together, smoothing all imperfections and casting marks. This means that the chamber is opened up all the way around, making for a much clearer entry for gasses into the cylinder and exit for the exhaust. I then flycut the heads to get the desired chamber CC's with.

I then use a flapwheel to remove the sharp edge all the way around. Take care not to round the sides where the cylinder will seal against the head. It is a good idea to scribe a line around the head where the cyl will meet the head, and to drop some junk valves into the heads to protect the valve seats while working in the chambers.

Use a cylinder to scribe or draw a line around the inside of the bore, marking where you perimeter to unshroud the valve. Compare this photo to the finished chamber photo later on. Unshrouding out to the scribe line. Non-plug side layback. Note that it is not as drastic as the plug side as there is less flow to be gained on this side. Finished chamber after polishing with a flapwheel. It is important to deburr all sharp edges in the chamber. I knock off the corners with the flapwheel.

This also shows the new "layback" angle of the chambers. Intake Ports. The goal is to provide the best port-match for a The stock size port does not need to be enlarged very much to get good results, and too big of a port will cause a loss of port velocity and create unwanted turbulence. The goal is to reduce the restriction of the port. Set the head in front of you with the intake flange facing you right side up. The ports are round, and we are going to make them oval in the direction of the sparkplug holes, similar to a "V" shape.

Hold the grinder perpendicular to the flange and open up the ports to the new port shape. Don't worry about blending into the port yet. Take your time and make all the port openings look the same. The right port is almost there.

Also note the angle of the rotary file is the same as the port entry angle, keeping things matched to the intake manifold later. Set the acorn file out as far as you can in the grinder to give maximum reach into the port.

On most heads the port has a casting part line right above the intake guide boss. This part line makes for a major corner right above the guide boss blocking any flow trying to go over top of the guide Bill Fisher's book has some good pictures of this area. You will want to blend this corner away by plunging the grinder down through the port going over top of the guide boss.

Once through, work from the chamber side of the port to blend the contour. There is a fair amount of metal to remove here so take your time and study the port closely. The goal is to make the port above the guide look like it does below the guide, in effect straightening the port. This will open up a new flow path for intake charge. I also like to thin the intake guide boss, as it does very little anyway. Not shown in this animation. Conversely, the closing of the valve does not immediately stop flow at the runner entrance, which continues completely unaffected until the signal that the valve closed reaches it.

The closing valve causes a buildup of pressure that travels up the runner as a positive wave. The runner entrance continues to flow at full speed, forcing the pressure to rise until the signal reaches the entrance. This very considerable pressure rise can be seen on the graph below, it rises far above atmospheric pressure. The principle is the same as in the water hammer effect so well known to plumbers. The speed that the signal can travel is the speed of sound within the runner.

That is, any time a change occurs in the cylinder - whether positive or negative - such as when the piston reaches maximum speed. For normal automotive design this point is almost always between 69 and 79 degrees ATDC, with higher rod ratios favoring the later position. At first glance this wave travel might seem to be blindingly fast and not very significant but a few calculations shows the opposite is true.

The engine using this system, running at rpm, takes a very considerable 46 crank degrees before any signal from the cylinder can reach the runner end assuming no movement of the air in the runner. This not only applies to the initial signal but to any and every change in the pressure or vacuum developed in the cylinder.

The answer lies at the end of the cycle when that big long runner now continues to flow at full speed disregarding the rising pressure in the cylinder and providing pressure to the cylinder when it is needed most. The runner length also controls the timing of the returning waves and cannot be altered.

A shorter runner would flow earlier but also would die earlier while returning the positive waves much too quickly and those waves would be weaker. The key is to find the optimum balance of all the factors for the engine requirements. Further complicating the system is the fact that the piston dome, the signal source, continually moves. First moving down the cylinder, thus increasing the distance the signal must travel.

Then moving back up at the end of the intake cycle when the valve is still open past BDC. The signals coming from the piston dome, after the initial runner flow has been established, must fight upstream against whatever velocity has been developed at that instant, delaying it further. The signals developed by the piston do not have a clean path up the runner either.

Large portions of it bounce off the rest of the combustion chamber and resonate inside the cylinder until an average pressure is reached. Also, temperature variations due to the changing pressures and absorption from hot engine parts cause changes in the local sonic velocity. When the valve closes, it causes a pile up of gas giving rise to a strong positive wave that must travel up the runner.

When the valve next opens, the remaining waves influence the next cycle. The two pressure traces are taken from the valve end blue and the runner entrance red. The blue line rises sharply as the intake valve closes. This causes a pile up of air, which becomes a positive wave reflected back up the runner and the red line shows that wave arriving at the runner entrance later. Note how the suction wave during cylinder filling is delayed even more by having to fight upstream against the inrushing air and the fact that the piston is further down the bore, increasing the distance.

The goal of tuning is to arrange the runners and valve timing so that there is a high-pressure wave in the port during the opening of the intake valve to get flow going quickly and then to have a second high pressure wave arrive just before valve closing so the cylinder fills as much as possible. The first wave is what is left in the runner from the previous cycle, while the second is primarily created during the current cycle by the suction wave changing sign at the runner entrance and arriving back at the valve in time for valve closing.

The factors involved are often contradictory and requires a careful balancing act to work. It is popularly held that enlarging the ports to the maximum possible size and applying a mirror finish is what porting is. However that is not so. Some ports may be enlarged to their maximum possible size in keeping with the highest level of aerodynamic efficiency but those engines are highly developed very high speed units where the actual size of the ports has become a restriction.

A mirror finish of the port does not provide the increase that intuition suggests. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer , which can alter the flow path noticeably, possibly increasing flow.

This is similar to what the dimples on a golf ball do. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow and in the interest of minimizing exhaust by-product build-up. A - Grit finish followed by a light buff is generally accepted to be representative of a near optimal finish for exhaust gas ports.

The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO see boundary layer and laminar flow. This is due to the wetting action of the air and indeed all fluids.

The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past, which develops a velocity profile or gradient across the duct. For surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center.

Only a very rough surface does this. In addition to all the considerations given to a four-stroke engine port, two-stroke engine ports have additional ones:. The die grinder is the stock in trade of the head porter and are used with a variety of carbide cutters, grinding wheels and abrasive cartridges. The complex and sensitive shapes required in porting necessitate a good degree of artistic skill with a hand tool. Until recently, CNC machining was used only to provide the basic shape of the port but hand finishing was usually still required because some areas of the port were not accessible to a CNC tool.

Measurement of the interior of the ports is difficult but must be done accurately. Sheet metal templates are made up, taking the shape from an experimental port, for both cross-sectional and lengthwise shape. Inserted in the port these templates are then used as a guide for shaping the final port. Even a slight error might cause a loss in flow so measurement must be as accurate as possible. Confirmation of the final port shape and automated replication of the port is now done using digitizing.

This kind of accuracy, repeatability, time has never before been possible. What used to take 18hrs. The internal aerodynamics involved in porting is counter-intuitive and complex. Successfully optimizing ports requires an air flow bench , a thorough knowledge of the principles involved, and engine simulation software. Although a large portion of porting knowledge has been accumulated by individuals using "cut and try" methods over time, the tools and knowledge now exist to develop a porting design with a measure of certainty.

Porting by inexperienced individuals without a full understanding of the fluid dynamics of the process still continues but the results are spotty and the process is expensive and time consuming with many more failures than successes. From Infogalactic: the planetary knowledge core.

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