Pt. 1
First off, porting (or porting and polishing as it's commonly called) is a process in which an effort is made to fill the cylinder with as much air fuel mixture (AFM) as possible. It seems very elementary, but with very few exceptions, every single effort is aimed at just that.
Now, we'll look at a port layout. The big port is your exhaust. The 2 small ports along the lower side of the exhaust are the main transfer ports (mains), the 2 behind that are the secondary transfer ports (secondaries), and the small port that sits across from the exhaust port is the boost port. Some applications have 2 exhaust ports that merge into one and have a bridge between them. Some have dual boost ports with a bridge between them. Generally found in aftermarket cylinders, there may also be 2 extra exhaust ports above the mains that also feed into the main exhaust port. More radical porting configurations may have tertiary transfer ports. For simplicity, lets stick to an exhaust, mains, secondaries, and a boost port.
A few common misconceptions are that porting is a process of boring each port out to the maximum possible size because it allows more air in. Though a larger port will flow more, that doesn't mean that all of the other factors to facilitate that maximum flow will exist. A smaller port will mean that the AFM enters the cylinder at a higher velocity. This is better because it reduces reversion (flowing back from where it came from) and purges the exhaust from the cylinder much better than a giant port. Again, this ultimately fills the cylinder with more of the AFM. Higher velocity also facilitates port aiming. If the ports are aimed toward the boost port (good) but are too large, velocity will be lost and momentum of the AFM will be very low and will be more subject to pressures that can alter their paths - AKA out of the exhaust port. A high velocity will mean the AFM has a higher inertia and will flow closer to the same direction that it initially flows.
Another misconception is that the ports are always polished. They may very well look sexy as anything else in existence, but that doesn't mean they work any better than an unpolished port. Some builders polish the exhaust port to a mirror finish. A smoother finish will have less surface area and will absolutely absorb less heat. Now the difference between a smooth port and a mirrored port may be very, very small, but it is absolutely there nonetheless. If you have time, go for it. If not, double check all of your other work.
Now for everything else, a slightly rough finish will help. The super tiny ridges in the surface will create concentrated micro turbulence and insulate (in a sense) the air from slowing as it would through a perfectly smooth surface. In addition, these tiny ridges also break up larger droplets of fuel that can fall out of the mixture and get them back into the flow of air.
Side note here: I've put into application a mix of rough and smooth finishes on the intake side. On inner radii, I'd smooth the surface to slow the flow and sort of pull it on around while the rough finish helped the air flow a little better. Did it work? I have no clue because my butt-dyno isn't that repeatable.
Now, for some considerations.
Requirements:
-Always, always, always have at least a few cans of carb cleaner available. This stuff cleans metal shavings out like magic. A toothbrush is a great option as well. A wire brush will work, but they bristles break and leave behind a little more than a toothbrush.
-Get some gloves and get a long sleeve shirt that cover all of your skin; metal shavings will make you very, very reluctant to every do anything like this again. Safety glasses are a must. I'm not even remotely joking. I literally started typing this JUST as I got back from the ER because of a metal shaving in my cornea at the end of a long scratch across my cornea. Not a fun day. Tetracane is the only thing keeping me from gouging my eye out right now. Get some safety glasses. The bigger and uglier, the better.
-Get at least 1 lamp that allows you to move it around (Pixar {can you believe that Pixar isn't in the Windows 8 dictionary? Go ahead and try it; it isn't in there. Little red squiggly line} lamp). 20 of these would be better. NO SHADOWS!!!!!
-Get something to grind with. For just a touch here and there, a small woodworking electric rotary tool from Home Depot will do just fine. Get a Dremel - I mean it, if you go this route, get a Dremel brand. I've tried 5-6 others and they won't last long and they vibrate. This route will be around $80-150. Another perk to a Dremel brand piece is that they have a right angle piece and an extension piece that attach for just a bit more. For more extensive work, Grizzly sells a woodworking kit that comes with a foot control, external electric motor, flex line, and a detachable grinder. This will cost $68 +S&H while on sale. The great thing about these are that they are easier to work with, they are smooth, and they accept the CC Specialty grinders. To be honest, each piece between a CCS kit and a Grizzly kit are interchangeable. My setup currently includes a Grizzly set with a Grizzly straight grinder and a CCS right angle grinder.
-Get a tungsten carbide bit (just call them carbides) with a round tip. This is the bare minimum requirement. 1 of each carbide from your closest HD or Lowes will be better of a start. To go in-depth, a set of extra-long carbides from online will do wonders. Remember, money spent here will pay off. Only once in my life have I cheaped out on carbides and gotten a quality product.
-A cheap piece of some hard material to place on your work surface can make clean-up a breeze. A white piece of indoor paneling is my personal favorite as I can write on it and take notes.
-A degree wheel is a must when altering heights unless you have someone that can give you a port map with heights. I also use machinists die to make marks on the cylinder with. I prefer to use a scalpel when marking them because it's very accurate.
-Lastly, get a permanent marker to mark any planned changes with. I always use black and green. Black means add material (epoxy or weld) and green means remove. I use black because it blends with the paint. If there are any grooves or depressions in the material that need filling, the black will keep your attention once you get into the cylinder. If you mess up a mark, carb cleaner gets it right off.
Planning
It should first be determined what you plan to gain with the port job. If you just have the cylinder off and are waiting on parts, a quick clean up of some casting flaws can't hurt. Now if you plan on making your blaster produce a powerband like a YFZ450, you'll may need a plan.
I'd like to recommend that if you're new to porting, try to look at your efforts as altering the current power delivery rather than making a screamer on your first go. I ported and ruined 2 cylinders before I ported anything that was even noticeably different. Picking a short, non-technical little area to ride. I have a group of 5-6 trees and an oak in my back yard that I circle. I try to leave the bike in question in a certain gear so that I become very, very familiar with the power delivery on that exact terrain. Things to notice are "falls off too fast below the powerband" or " doesn't break the tires loose here, but it does there", or "hits the powerband exactly HERE after this curve. These tell you quite a bit about the changes you need.
We'll get into how port geometry affects power later, but these notes are crucial.
First off, porting (or porting and polishing as it's commonly called) is a process in which an effort is made to fill the cylinder with as much air fuel mixture (AFM) as possible. It seems very elementary, but with very few exceptions, every single effort is aimed at just that.
Now, we'll look at a port layout. The big port is your exhaust. The 2 small ports along the lower side of the exhaust are the main transfer ports (mains), the 2 behind that are the secondary transfer ports (secondaries), and the small port that sits across from the exhaust port is the boost port. Some applications have 2 exhaust ports that merge into one and have a bridge between them. Some have dual boost ports with a bridge between them. Generally found in aftermarket cylinders, there may also be 2 extra exhaust ports above the mains that also feed into the main exhaust port. More radical porting configurations may have tertiary transfer ports. For simplicity, lets stick to an exhaust, mains, secondaries, and a boost port.
A few common misconceptions are that porting is a process of boring each port out to the maximum possible size because it allows more air in. Though a larger port will flow more, that doesn't mean that all of the other factors to facilitate that maximum flow will exist. A smaller port will mean that the AFM enters the cylinder at a higher velocity. This is better because it reduces reversion (flowing back from where it came from) and purges the exhaust from the cylinder much better than a giant port. Again, this ultimately fills the cylinder with more of the AFM. Higher velocity also facilitates port aiming. If the ports are aimed toward the boost port (good) but are too large, velocity will be lost and momentum of the AFM will be very low and will be more subject to pressures that can alter their paths - AKA out of the exhaust port. A high velocity will mean the AFM has a higher inertia and will flow closer to the same direction that it initially flows.
Another misconception is that the ports are always polished. They may very well look sexy as anything else in existence, but that doesn't mean they work any better than an unpolished port. Some builders polish the exhaust port to a mirror finish. A smoother finish will have less surface area and will absolutely absorb less heat. Now the difference between a smooth port and a mirrored port may be very, very small, but it is absolutely there nonetheless. If you have time, go for it. If not, double check all of your other work.
Now for everything else, a slightly rough finish will help. The super tiny ridges in the surface will create concentrated micro turbulence and insulate (in a sense) the air from slowing as it would through a perfectly smooth surface. In addition, these tiny ridges also break up larger droplets of fuel that can fall out of the mixture and get them back into the flow of air.
Side note here: I've put into application a mix of rough and smooth finishes on the intake side. On inner radii, I'd smooth the surface to slow the flow and sort of pull it on around while the rough finish helped the air flow a little better. Did it work? I have no clue because my butt-dyno isn't that repeatable.
Now, for some considerations.
Requirements:
-Always, always, always have at least a few cans of carb cleaner available. This stuff cleans metal shavings out like magic. A toothbrush is a great option as well. A wire brush will work, but they bristles break and leave behind a little more than a toothbrush.
-Get some gloves and get a long sleeve shirt that cover all of your skin; metal shavings will make you very, very reluctant to every do anything like this again. Safety glasses are a must. I'm not even remotely joking. I literally started typing this JUST as I got back from the ER because of a metal shaving in my cornea at the end of a long scratch across my cornea. Not a fun day. Tetracane is the only thing keeping me from gouging my eye out right now. Get some safety glasses. The bigger and uglier, the better.
-Get at least 1 lamp that allows you to move it around (Pixar {can you believe that Pixar isn't in the Windows 8 dictionary? Go ahead and try it; it isn't in there. Little red squiggly line} lamp). 20 of these would be better. NO SHADOWS!!!!!
-Get something to grind with. For just a touch here and there, a small woodworking electric rotary tool from Home Depot will do just fine. Get a Dremel - I mean it, if you go this route, get a Dremel brand. I've tried 5-6 others and they won't last long and they vibrate. This route will be around $80-150. Another perk to a Dremel brand piece is that they have a right angle piece and an extension piece that attach for just a bit more. For more extensive work, Grizzly sells a woodworking kit that comes with a foot control, external electric motor, flex line, and a detachable grinder. This will cost $68 +S&H while on sale. The great thing about these are that they are easier to work with, they are smooth, and they accept the CC Specialty grinders. To be honest, each piece between a CCS kit and a Grizzly kit are interchangeable. My setup currently includes a Grizzly set with a Grizzly straight grinder and a CCS right angle grinder.
-Get a tungsten carbide bit (just call them carbides) with a round tip. This is the bare minimum requirement. 1 of each carbide from your closest HD or Lowes will be better of a start. To go in-depth, a set of extra-long carbides from online will do wonders. Remember, money spent here will pay off. Only once in my life have I cheaped out on carbides and gotten a quality product.
-A cheap piece of some hard material to place on your work surface can make clean-up a breeze. A white piece of indoor paneling is my personal favorite as I can write on it and take notes.
-A degree wheel is a must when altering heights unless you have someone that can give you a port map with heights. I also use machinists die to make marks on the cylinder with. I prefer to use a scalpel when marking them because it's very accurate.
-Lastly, get a permanent marker to mark any planned changes with. I always use black and green. Black means add material (epoxy or weld) and green means remove. I use black because it blends with the paint. If there are any grooves or depressions in the material that need filling, the black will keep your attention once you get into the cylinder. If you mess up a mark, carb cleaner gets it right off.
Planning
It should first be determined what you plan to gain with the port job. If you just have the cylinder off and are waiting on parts, a quick clean up of some casting flaws can't hurt. Now if you plan on making your blaster produce a powerband like a YFZ450, you'll may need a plan.
I'd like to recommend that if you're new to porting, try to look at your efforts as altering the current power delivery rather than making a screamer on your first go. I ported and ruined 2 cylinders before I ported anything that was even noticeably different. Picking a short, non-technical little area to ride. I have a group of 5-6 trees and an oak in my back yard that I circle. I try to leave the bike in question in a certain gear so that I become very, very familiar with the power delivery on that exact terrain. Things to notice are "falls off too fast below the powerband" or " doesn't break the tires loose here, but it does there", or "hits the powerband exactly HERE after this curve. These tell you quite a bit about the changes you need.
We'll get into how port geometry affects power later, but these notes are crucial.