Why would you choose hand porting over CNC?
The first thing you have to understand is that CNC machines can’t port heads! They can only copy what the original head porter did. This is called reverse engineering.
Hand porting or custom ported heads and manifolds are better in the respect that the individual doing the work knows your particular application, cam and other pertinent facts concerning your engine. Hence, the heads will produce a better power curve than a universal CNC computer program.
Because the CNC machine cannot actually port a head in the same way as an expert Air-Flow Technician can, the process of making a program to port heads in a CNC machine is very involved and necessarily expensive. And these costs have to be recovered in the end product.
1) The head must be hand ported and flowed. This process can take days, weeks, or months until a satisfactory shape is derived that will perform to the engine builders specifications.
2) The head and port shapes have to be digitized (Scanned). This as an on-line process takes about 14 hour’s, while in an off-line machine takes about 8 hour’s. However, the cost of the off-line machine can be upwards of $20,000.00 dollars, and requires a trained operator.
3) Once this program is completed, it has to be transferred into another computer with a Cad-Cam software application, which costs upwards of $15,000.00 dollars for one that can compute a 5-Axis program, plus the cost of the computer. Once the scanned configuration is loaded into the Cad-Cam program it is corrected for irregularities, imperfections and is generally smoothed out. Once this is accomplished, a machining program is designed to tell the machine where to go and what and when to cut, how fast to cut it and which tool to use. The program also has to tell the head fixture what to do so that the cutter will remain in contact with the head at all times and not make contact with the tool shank or the machine itself. This process can take 14 or so hours. Computer programmers are in short supply and highly paid ($40 to $60 dollars per hour).
4) Once the machining program is established and approved, it is tested to see if it will run correctly. Once this is accomplished, the 5-Axis CNC Machining Center is ready to machine the head. Unfortunately, the program can only machine that particular head and only in that particular way. But it will do an endless array of them in the very exact way to the thousandth of an inch.
OK! Now you’re wondering about the machining center itself?
There are three types of CNC machining centers:
1) Horizontal – these are generally made in 4-Axis mode.
2) Vertical – these are generally only 3-Axis and have to be converted to 4 & 5 Axis
3) Vertical 5-Axis
The state of the art is the vertical 5-Axis but there are many acceptable horizontal machines that will do the job. Here the cost decides what to buy. Both of these machines are going to cost from $200,000.00 to $500,000.00 dollars. The 3-Axis vertical machine capable of doing heads is going to cost between $70,000.00 and $100,000.00. Then there is an additional cost for installing the fourth and fifth axis, which is in the neighborhood of $15,000.00 dollars. Unfortunately, even in this configuration the 3-Axis machine can’t do heads without a complex fixture that rotates in two directions. It requires two rotary heads, one that teeter-totters, and one that rotates 360. The base fixture costs about $70,000.00 and the rotary table’s can cost between $20,000.00 and $60,000.00 apiece, depending on the quality and durability.
Now at an approximate cost $300,000.00 dollars you are ready to port heads in a CNC machining center.
But, do you have any work?
Do you have employees that can run the equipment?
If you are a start up then you have to have more money for advertising, paying employees, paying a real head porter to design heads for you to copy!
Alternatively, you have to buy already ported heads and steal (reverse engineer) the configuration.
On the other hand, you could hire a real head porter, buy a flow bench and build him a room to do his work.
What other equipment would you need to finish heads?
You have to get a Serdi machine, a surfacing machine, cleaning machines, and a variety of other cylinder-head related items to the tune of another $100,000.00 bucks.
Next thing you have to consider is how many heads are there, and how many different port configurations are there for each of these heads? Then you have to make the decision about how many of them do you really want to do.
Do you want to be able to do whatever comes in the door?
Something else you may want to know about the CNC porting of heads is that if you already have a pair of heads running on your engine and want them ported can the CNC machine port your heads?
If the heads have been extensively milled (Surfaced) the probability is that the CNC machine cannot port your heads is realistic. If they have been angle milled you know for a fact that the CNC machine cannot.
This means that if you want your heads ported and polished you are going to have to find someone that does them by hand. Then does this person have a flow bench and how long has he been using it?
Why can’t the CNC machine port my heads?
Because it uses a computer program and if the program does not have a compensation for the deck to valve-seat dimension then the port work inside the bowl area won’t come out correctly, and it is the short side radius that controls the flow through the valve. If the heads have been angle milled then the whole head is out of dimension and the machine can’t compensate for that thus the porting job becomes junk.
Realistically, if you are a qualified head technician, trained by someone in the field, or by Mondello’s technical school then you don’t have to worry about what type of head to do. You just have to do one cylinder and flow it then go to the next one and so forth and so on. However, you do have to provide yourself with the correct equipment.
As cylinder head technician’s we are faced with this “Propaganda” concerning CNC-Porting and how do we contend with the falling price structure applied to our work?
Real head porting is an art, and a science combined. It takes years of practice just to be able to hold the proportions within the ports to a minimum tolerance and keep the vertical and horizontal lines uniform. Then knowing how to reduce the cutter-marks to a minimum so that the polishing work looks shiny and nice takes a considerable amount of time or at least good training. Personally I’ve trained many head porters and found that it takes at least two years working eight hours a day to be able to accomplish the quality of work I required. A quality head must look good, have evenly proportioned intake and exhaust ports, combustion chambers that allow the intake charge to flow into the cylinder properly and to collect the exhaust gasses into and under the exhaust valve efficiently. It must also have the specific flow characteristics that the engine-builder wants for his particular engine.
What controls this configuration?
The question sounds simple but it’s not, for instance:
What type of cam are you going to use, hydraulic, roller or flat tappet, mechanical, roller or flat tappet. If it’s a flat tappet what diameter is the lifter? What is the lift and duration, what are the timing events?
What is the engine going to be used for is it supercharged, or naturally aspirated, are you going to use N20? If supercharged is it an Engine driven centrifugal, Turbo, Roots, or other? If it’s naturally aspirated what is it going to use for induction; carburetors, how many and what type of manifold; fuel injection, what type and what type of manifold.
What is the displacement of the engine in question, have you chosen the correct head for that application? What valve size is going to make that head perform to its highest potential, in the application you intend for it? What horsepower and torque do you anticipate making, and are they realistic?
These are just some of the questions that have to answered to get a cylinder head to perform at its optimum potential.
Sincerely,
Denny Schmidt
July, 8 2006
Innovations For Internal Combustion Engines Through Air-Flow Technology
The first thing you have to understand is that CNC machines can’t port heads! They can only copy what the original head porter did. This is called reverse engineering.
Hand porting or custom ported heads and manifolds are better in the respect that the individual doing the work knows your particular application, cam and other pertinent facts concerning your engine. Hence, the heads will produce a better power curve than a universal CNC computer program.
Because the CNC machine cannot actually port a head in the same way as an expert Air-Flow Technician can, the process of making a program to port heads in a CNC machine is very involved and necessarily expensive. And these costs have to be recovered in the end product.
1) The head must be hand ported and flowed. This process can take days, weeks, or months until a satisfactory shape is derived that will perform to the engine builders specifications.
2) The head and port shapes have to be digitized (Scanned). This as an on-line process takes about 14 hour’s, while in an off-line machine takes about 8 hour’s. However, the cost of the off-line machine can be upwards of $20,000.00 dollars, and requires a trained operator.
3) Once this program is completed, it has to be transferred into another computer with a Cad-Cam software application, which costs upwards of $15,000.00 dollars for one that can compute a 5-Axis program, plus the cost of the computer. Once the scanned configuration is loaded into the Cad-Cam program it is corrected for irregularities, imperfections and is generally smoothed out. Once this is accomplished, a machining program is designed to tell the machine where to go and what and when to cut, how fast to cut it and which tool to use. The program also has to tell the head fixture what to do so that the cutter will remain in contact with the head at all times and not make contact with the tool shank or the machine itself. This process can take 14 or so hours. Computer programmers are in short supply and highly paid ($40 to $60 dollars per hour).
4) Once the machining program is established and approved, it is tested to see if it will run correctly. Once this is accomplished, the 5-Axis CNC Machining Center is ready to machine the head. Unfortunately, the program can only machine that particular head and only in that particular way. But it will do an endless array of them in the very exact way to the thousandth of an inch.
OK! Now you’re wondering about the machining center itself?
There are three types of CNC machining centers:
1) Horizontal – these are generally made in 4-Axis mode.
2) Vertical – these are generally only 3-Axis and have to be converted to 4 & 5 Axis
3) Vertical 5-Axis
The state of the art is the vertical 5-Axis but there are many acceptable horizontal machines that will do the job. Here the cost decides what to buy. Both of these machines are going to cost from $200,000.00 to $500,000.00 dollars. The 3-Axis vertical machine capable of doing heads is going to cost between $70,000.00 and $100,000.00. Then there is an additional cost for installing the fourth and fifth axis, which is in the neighborhood of $15,000.00 dollars. Unfortunately, even in this configuration the 3-Axis machine can’t do heads without a complex fixture that rotates in two directions. It requires two rotary heads, one that teeter-totters, and one that rotates 360. The base fixture costs about $70,000.00 and the rotary table’s can cost between $20,000.00 and $60,000.00 apiece, depending on the quality and durability.
Now at an approximate cost $300,000.00 dollars you are ready to port heads in a CNC machining center.
But, do you have any work?
Do you have employees that can run the equipment?
If you are a start up then you have to have more money for advertising, paying employees, paying a real head porter to design heads for you to copy!
Alternatively, you have to buy already ported heads and steal (reverse engineer) the configuration.
On the other hand, you could hire a real head porter, buy a flow bench and build him a room to do his work.
What other equipment would you need to finish heads?
You have to get a Serdi machine, a surfacing machine, cleaning machines, and a variety of other cylinder-head related items to the tune of another $100,000.00 bucks.
Next thing you have to consider is how many heads are there, and how many different port configurations are there for each of these heads? Then you have to make the decision about how many of them do you really want to do.
Do you want to be able to do whatever comes in the door?
Something else you may want to know about the CNC porting of heads is that if you already have a pair of heads running on your engine and want them ported can the CNC machine port your heads?
If the heads have been extensively milled (Surfaced) the probability is that the CNC machine cannot port your heads is realistic. If they have been angle milled you know for a fact that the CNC machine cannot.
This means that if you want your heads ported and polished you are going to have to find someone that does them by hand. Then does this person have a flow bench and how long has he been using it?
Why can’t the CNC machine port my heads?
Because it uses a computer program and if the program does not have a compensation for the deck to valve-seat dimension then the port work inside the bowl area won’t come out correctly, and it is the short side radius that controls the flow through the valve. If the heads have been angle milled then the whole head is out of dimension and the machine can’t compensate for that thus the porting job becomes junk.
Realistically, if you are a qualified head technician, trained by someone in the field, or by Mondello’s technical school then you don’t have to worry about what type of head to do. You just have to do one cylinder and flow it then go to the next one and so forth and so on. However, you do have to provide yourself with the correct equipment.
As cylinder head technician’s we are faced with this “Propaganda” concerning CNC-Porting and how do we contend with the falling price structure applied to our work?
Real head porting is an art, and a science combined. It takes years of practice just to be able to hold the proportions within the ports to a minimum tolerance and keep the vertical and horizontal lines uniform. Then knowing how to reduce the cutter-marks to a minimum so that the polishing work looks shiny and nice takes a considerable amount of time or at least good training. Personally I’ve trained many head porters and found that it takes at least two years working eight hours a day to be able to accomplish the quality of work I required. A quality head must look good, have evenly proportioned intake and exhaust ports, combustion chambers that allow the intake charge to flow into the cylinder properly and to collect the exhaust gasses into and under the exhaust valve efficiently. It must also have the specific flow characteristics that the engine-builder wants for his particular engine.
What controls this configuration?
The question sounds simple but it’s not, for instance:
What type of cam are you going to use, hydraulic, roller or flat tappet, mechanical, roller or flat tappet. If it’s a flat tappet what diameter is the lifter? What is the lift and duration, what are the timing events?
What is the engine going to be used for is it supercharged, or naturally aspirated, are you going to use N20? If supercharged is it an Engine driven centrifugal, Turbo, Roots, or other? If it’s naturally aspirated what is it going to use for induction; carburetors, how many and what type of manifold; fuel injection, what type and what type of manifold.
What is the displacement of the engine in question, have you chosen the correct head for that application? What valve size is going to make that head perform to its highest potential, in the application you intend for it? What horsepower and torque do you anticipate making, and are they realistic?
These are just some of the questions that have to answered to get a cylinder head to perform at its optimum potential.
Sincerely,
Denny Schmidt
July, 8 2006
Innovations For Internal Combustion Engines Through Air-Flow Technology
I'm tempted to move this as there really isn't any "tech" information included, it's not a how to.... it's merely how his business is set up and what questions he needs answered before he can recommend a head job. I did get a PM from him and I let the post stay on the forum. It may be better off in the vendor section.
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