head porting
Just wanted to throw out some stuff to be careful of when porting at home.
Go Easy
About as ambitious as you should get for your first porting job is to blend seats into the port, skinny down guide bosses and de-shroud the intake valve by about a sixteenth of an inch. After this, just clean up the rest of the ports and chambers with course emery rolls.
Take Your Time
Porting takes time and aluminum cuts faster than iron. Figure (with the recommended tools) spending about 8-12 hours on the actual porting job. To avoid wasting time on half a job ask yourself the following: are you good for completion and are the heads crack-free.
Shape It, Don't Shine It
Pro-ported heads often have a high shine finish, but understand that this is done to add perceived value for those with limited porting knowledge. It is shape not shine that makes horsepower.
Use Correct Tools
The right porting tools must be used or you will be defeated before ever starting. A small eighth-inch collet and an electric die-grinder is totally inadequate because they lack power. If you have an air compressor, an inexpensive air die grinder is the way to go for fast metal removal. Since shine is not on the agenda, only 60 and 80 grit emery rolls and flat pads for finish work will be needed. If no air access exists then (though more cumbersome and expensive) an electric die grinder is the answer.Although carbides are often best spun at 15,000 -22,000 rpm, the same cannot be said for emery rolls and the like. For either air or electric, some form of speed reduction is essential. For an air-powered grinder, a cheap pressure regulator gets the job done. Although not intended for such, a light dimmer switch is a cheap and effective answer to speed control for an electric die grinder.
Cheap high-speed steel cutters are available from many cut-price tool stores. Unfortunately they are totally inadequate for the job. In this area it is true to say that anything cheap will not work. Your cutters must be carbide and, while not expensive, they are certainly not cheap. Two places that have excellent prices and cutters explicitly for cutting heads are CHA (Cylinder Head Abrasives) and Roger Helgesen. The porting mods described here need only two or three cutters to get the job done. These are a three-eighths and half-inch olive and a three-eighths ball. For cast iron, you will need a fine-tooth form and for aluminum a course tooth. To reduce cutters loading up when working aluminum, a kerosene/WD-40 mix can be used, but to completely eliminate loading and to speed cutting, the special fluid sold by Roger Helgesen is the choice of pros.Chamber reworking calls for seat protection. This is best done utilizing valves of the appropriate size having the seats ground with only a few thousands margin left for a near flush fit in the chamber.
Machining
Unless you intend to rework a pair of new heads, do not overlook the fact they may need machine work done. If the CR is to be raised while retaining the pistons currently in the motor then, even new heads, will need at least a milling operation. The most likely job that will have to be done on an OE head is a new valve seat job, but there are exceptions. Some factory existing seat jobs are sufficiently wide (an eighth inch) to allow the inside edge to be radiused into the port body. If so then a new seat job is not essential. If the heads being reworked are used, then they may require face milling to true them up. Your machine shop can check this out for you with a machinist's straight edge. If you are looking for more compression then the head can usually be faced 40-60 thousandths-if the casting is good for it. However, doing so will mean the intake manifold will have to be machined to realign the ports.
Guides Are Critical
If the guides are worn or the seat design is far removed from a 3-angle pattern or is worn, then a guide job and seat re-cutting will be mandatory. Be aware that worn guides can cost as much as 10-15 hp and can also lead to the head coming off the valve. Do not use guide knurling as a fix for worn guides as this does not last and compromises exhaust valve stem heat transfer. Just bite the bullet on this one and go for new cast-iron or bronze guides as it will pay off.
Safety First
A carbide cutter driven at high speed means high-speed chips of metal flying around. If you do not protect your eyes with safety glasses, a hospital visit is an absolute certainty. When it comes time to use emery on your head casting, be sure to wear a mask to filter out the dust and metal particles. Even short exposure times can cause respiratory problems. To assist keeping the air you breath and that around your workspace clean, use a shop vac to suck the work debris directly out of the ports as you work.
Keep It Clean
After grinding a couple of sets of heads in a work area, getting rid of the resulting grit and metal dust is a major job. Use an enclosed workspace that is completely separate from wherever you may subsequently build your engine.
Go Easy
About as ambitious as you should get for your first porting job is to blend seats into the port, skinny down guide bosses and de-shroud the intake valve by about a sixteenth of an inch. After this, just clean up the rest of the ports and chambers with course emery rolls.
Take Your Time
Porting takes time and aluminum cuts faster than iron. Figure (with the recommended tools) spending about 8-12 hours on the actual porting job. To avoid wasting time on half a job ask yourself the following: are you good for completion and are the heads crack-free.
Shape It, Don't Shine It
Pro-ported heads often have a high shine finish, but understand that this is done to add perceived value for those with limited porting knowledge. It is shape not shine that makes horsepower.
Use Correct Tools
The right porting tools must be used or you will be defeated before ever starting. A small eighth-inch collet and an electric die-grinder is totally inadequate because they lack power. If you have an air compressor, an inexpensive air die grinder is the way to go for fast metal removal. Since shine is not on the agenda, only 60 and 80 grit emery rolls and flat pads for finish work will be needed. If no air access exists then (though more cumbersome and expensive) an electric die grinder is the answer.Although carbides are often best spun at 15,000 -22,000 rpm, the same cannot be said for emery rolls and the like. For either air or electric, some form of speed reduction is essential. For an air-powered grinder, a cheap pressure regulator gets the job done. Although not intended for such, a light dimmer switch is a cheap and effective answer to speed control for an electric die grinder.
Cheap high-speed steel cutters are available from many cut-price tool stores. Unfortunately they are totally inadequate for the job. In this area it is true to say that anything cheap will not work. Your cutters must be carbide and, while not expensive, they are certainly not cheap. Two places that have excellent prices and cutters explicitly for cutting heads are CHA (Cylinder Head Abrasives) and Roger Helgesen. The porting mods described here need only two or three cutters to get the job done. These are a three-eighths and half-inch olive and a three-eighths ball. For cast iron, you will need a fine-tooth form and for aluminum a course tooth. To reduce cutters loading up when working aluminum, a kerosene/WD-40 mix can be used, but to completely eliminate loading and to speed cutting, the special fluid sold by Roger Helgesen is the choice of pros.Chamber reworking calls for seat protection. This is best done utilizing valves of the appropriate size having the seats ground with only a few thousands margin left for a near flush fit in the chamber.
Machining
Unless you intend to rework a pair of new heads, do not overlook the fact they may need machine work done. If the CR is to be raised while retaining the pistons currently in the motor then, even new heads, will need at least a milling operation. The most likely job that will have to be done on an OE head is a new valve seat job, but there are exceptions. Some factory existing seat jobs are sufficiently wide (an eighth inch) to allow the inside edge to be radiused into the port body. If so then a new seat job is not essential. If the heads being reworked are used, then they may require face milling to true them up. Your machine shop can check this out for you with a machinist's straight edge. If you are looking for more compression then the head can usually be faced 40-60 thousandths-if the casting is good for it. However, doing so will mean the intake manifold will have to be machined to realign the ports.
Guides Are Critical
If the guides are worn or the seat design is far removed from a 3-angle pattern or is worn, then a guide job and seat re-cutting will be mandatory. Be aware that worn guides can cost as much as 10-15 hp and can also lead to the head coming off the valve. Do not use guide knurling as a fix for worn guides as this does not last and compromises exhaust valve stem heat transfer. Just bite the bullet on this one and go for new cast-iron or bronze guides as it will pay off.
Safety First
A carbide cutter driven at high speed means high-speed chips of metal flying around. If you do not protect your eyes with safety glasses, a hospital visit is an absolute certainty. When it comes time to use emery on your head casting, be sure to wear a mask to filter out the dust and metal particles. Even short exposure times can cause respiratory problems. To assist keeping the air you breath and that around your workspace clean, use a shop vac to suck the work debris directly out of the ports as you work.
Keep It Clean
After grinding a couple of sets of heads in a work area, getting rid of the resulting grit and metal dust is a major job. Use an enclosed workspace that is completely separate from wherever you may subsequently build your engine.