Porting basics

[tfaith08]

As a first post, I figured that I'd post what I posted on Blasterforum.com.

 

 

Preface

 

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.

Technique

-BE CONSERVATIVE

-Make incremental changes here and there. Don't try to completely alter the port geometry off the bat. Those small changes will give you a feel for your grinder and how your bit cuts. This is why I recommend that you get a round tipped carbide; if you slip, you don't cut a huge gash. A round tip will grab in a much different fashion than a flat or pointed tip.

-Hold the grinder in a way that allows you to have complete control. When possible, I like to hold the grinder at the back with my left hand and guide it with my right hand while both hands are planted on a solid surface.

-Don't stop moving. Don't cover the same area over and over. This will create deep grooves. Try going over an area for a few seconds and then changing angles and going over the same and surrounding areas. This will help you fight those pits. When moving side to side, don't switch left to right or right to left at the same spot over and over. You'll be looking at the middle of the area where you're doing just fine at not creating a pit, while you're creating 2 pits on either side. Eventually, you can make long passes without a problem.

-Listen to the grinder. If it's dropping more than just a hair, you're going too fast. Take your time.

-Approach corners and ridges with a constant motion and a sure grip just above your grinding point. Press down when you're ready to grind rather than resting where you grind. This will let you control the grinder much more accurately. The corners and ridges are important, but don't let it scare you. A few slight mess-ups won't be noticeable. Several bad ones throughout will likely be.

-Most carbides don't like to be used head-on. Use them at an angle. Most like to jump when you touch the tip wrong (right, guys?).

-If you slip or if the carbide catches and runs away up a wall or over a corner, try to decide whether it can be saved or whether the whole surface will be compromised by smoothing out one tiny groove. One tiny screw up will never be seen or noticed on the butt-dyno.

-Be patient. A fast port job will likely mean that you miss something (unless you're GOOD). I port my cylinders over the course of a week or so. I'll grind the obvious stuff and then sit on each decision point. Let it digest. Looking at other port jobs will give you ideas that you can try. The guy that taught me said that the fastest port job he's ever done was over 2 days. Sure, people can do it in 3-4 hours, but they're better than you and I and they have a business to run that allows them to get really good and fast at it. If you have to rush a port job, you shouldn't have started in the first place. Hell, I took the 250R cylinder that I'm porting to work with me today just to look at and think about. It came home with a few black and green marks.

-If you add epoxy, use Devcon when you're close to the cylinder and JB weld when more than 2" away. They expand at similar rates to their surrounding area when placed that way. Try to add at least 2-3mm when you do add it. This allows it to set well. Try to keep it built up as much as possible without compromising your shapes. If you add some to your transfers, smooth the epoxy over while ADDING to the transfer shape. I've found that only leaving a very small amount (.5mm or less) can let the epoxy break away (ask me how I know). Sanding with a 40 grit finish or taking your square tip carbide and placing some anchor holes will help it stick when it cures.



Figuring out what you have

With the head off and the cylinder on (for those who want to alter widths and heights), install your degree wheel. Mark down what you measure somewhere that you can make sure you'll have it later. This means that if you use that piece of white paneling that I mentioned before, don't write it down in pencil there. I prefer to write everything down in a notebook for future reference. I like to mark the port walls at the angle they come into the cylinder in a continuous line on the piston top. This allows me to see were I can and can't remove material (piston ring ends for example) and tells me the true shape of the port at the cylinder. I then mark those lines with a dot from a marker.

Once you have everything marked and you have your head studs out, rotate the piston to TDC and measure your ports. When you have angled ports (you will, trust me), measure in a perpendicular line from the marks. This will give you a more accurate idea of how wide your ports are. For example, your mains will be angled toward the rear of the cylinder. If you look at them from the center of the cylinder, they look pretty wide. However, when viewed from the from directly in front of the port, they are actually much smaller. Note that the cylinder is angled much more rearward than then main transfer port itself is. This is a sort of kicker to get the AFM to the back of the cylinder.

 

Alterations: Durations and area

-BE CONSERVATIVE

Let me state this before you read any further. Every builder has a method and a set of numbers they like to see. I got my start by looking at the numbers that others tried and their results. I then modified them to fit my style of porting and though I don't recommend you take anything I have to say as a rule of thumb, this is the way that I've come to find great results for myself. I was very fortunate to have a multiple world record holding builder take me under his wing. Am I as good as KOR, LED, or Flotek? No, but I'm happy with what I can do (as are a few others )

I always start designing my ports with the exhaust port height. Most exhaust ports are close to 178-182 degrees of exhaust port duration. If I need more top end power, raising the exhaust port will generally shift the powerband to the right. Too much duration will make your powerband peaky. This is in part because of the height difference between the exhaust and the transfers and boost port. I generally widen the exhaust port to around 2-3mm of clearance between the exhaust port and the exhaust side of the mains. I try to keep all of my corners somewhat rounded unless I don't want to increase duration or if I'm getting too close to the mains. In this case, I'll reduce the radius on the corners just a little. A short life, all out screamer will typically have square ports with a 1mm radius or less on every corner.

If you're working on a bridged exhaust port, be cognizant of your bridge. If you narrow it too much, you'll reduce the ability of it to shed heat to the surrounding area. This will cause it to bulge into your piston. After honing the cylinder, I like to take 180 grit sand paper to the cylinder on the bridge just for a few seconds to remove enough material to compensate. Again, reducing the radii on the bridge can reduce the ability to shed heat. Be conservative.

Blowdown is the time between exhaust opening and transfer opening measured in degrees. I prefer around 28-31 degrees, but don't take that as the golden rule; that's what I like to see. This means that if I have 180 degrees of exhaust duration, I'd like to have 118-124 degrees of transfer timing for a blowdown within my range. Old Suzuki and Yamaha bikes had huge blowdown periods and had gobs of peak power but no power above and below peak. Less blowdown GENERALLY means a wider powerband TO AN EXTENT. Too short and peak power will suffer and over-rev will vanish.

After I have my exhaust duration, I can look at what I want for transfer duration. Say I go with 188 degrees and I want to raise my transfer ports. If I read 132 degrees on my timing wheel, I'll have 28 degrees of blowdown. This puts it within the range that I LIKE TO SEE. If my transfers are at 132, I'll be happy with anywhere from 188-194 degrees of exhaust duration.

Now as stated above, I start with exhaust. After I get that figure and determine whether my transfer ports are within my blowdown preference range, I look at width. My rule for width loosely considers Gordon Jennings's Port-Time Area (PTA) concept. I prefer this a bit morehttp://www.dragonfly75.com/motorbike/formulas.html), but still, this is a loose consideration of mine. My largest factor here is the port shape from bottom to top. If I need to grind the cylinder back some to allow for the shape I'm after, I'll reference PTA to ensure that I'm within the limits before I cut.

Staggering the port durations can assist in power spread. If performed improperly, it can ruin the engine (like everything else to do with porting). I don't have very much experience here, but I've seen it done and it does work. I've never seen a difference in staggering of more than 2 total degrees. IIRC, the example that comes to mind is 188 exhaust, 130 main, 132 secondary, 130 boost. Don't go too radical here.



Alterations: shaping

Now, I like to aim my ports as much as possible to the rear of the cylinder. This is for a few reasons. Once all of the AFM piles up at the back of the cylinder, the boost port will help push it upward, purging the cylinder further. Yes, the expansion chamber does the suck and blow thing (haha), but it really blows more below the powerband and sucks too much in over-rev. Aiming the ports rearward will help with filling the cylinder with more AFM and less exhaust (remember the first paragraph?). This will broaden your powerband. From my experience, this doesn't really affect peak power that much, but it does affect power delivery everywhere else. As for grinding, this may mean removing some material to allow the port to aim the charge in a more desirable path. For you first timers, this can also mean not cutting that one part down to give you that ever so perfect flow divider from some shit you saw in a NASA picture. Sometimes, leaving an area alone can allow it to function much better in conjunction with other areas. This goes back to "be conservative".

Now if you consider this for a minute, you'll appreciate an extensive port job much more. If you cut a hole in a piece of paper and blow through it, how well does that path of hot breath stay together and pile up? Not well, huh? Now if you take a piece of tubing and blow through it, you can see that it focuses the path much more effectively. This is why ports that are flatter as a whole while entering the cylinder have more velocity and a wider powerband in general. This takes serious time in most cases.

MacDizzy mentioned this quite a few times on his site. I've also seen a few applications where the outside of the ports were cut through entirely and epoxied over just to accomplish this. From what I've seen, it does work well. The preferred way is to add material to the inside radius and remove from the outside before merging into a flat port.

Now the roof angle matters as well. An angle of 5 degrees on the roof can make a noticeable difference in some applications. I prefer 0-5 degrees on the transfer roofs. A flat roof will contribute more to peak power at higher RPM, while a 3-4 degree roof will spread the power around some. As for the boost port, I've never tried much, but I've never had a reason to. They work just fine like they are stock for me with just port-matching the sleeve to the cylinder. The largest reason that I don't have much experience with boost ports is because I haven't done very much to them before. Maybe someone else can chime in here.

Lastly, bevel all of your ports. A .5-1mm wide bevel that's .2-.5mm deep has always sufficed for me. Being a little generous with the exhaust bevel is fine.


Side notes:

-No explanation as to why, but the builder who taught me said, "no knife edges except occasionally". Sadly, he hasn't explained what fell into the occasionally category quite yet.

-Keep structural integrity in mind.

-Lots of small changes equals one big change

-It's a lot easier to not cut something than it is to put it back. Be conservative.

-80-180 grit in a perpendicular direction to travel is great. I always mirror polish my exhaust because I have time 9/10. Otherwise, a 200 grit finish is more than enough.

-If you see carbon buildup in the exhaust, flow probably isn't doing too well in that spot.

Power hides within the design of the transfers
 

-The guy that taught me really stressed that the biggest gains were in the curves.

-If you can't figure out what you want for your duration or width, look at other builds from professionals. They've done the trial and error. Learning what works is much more time efficient than learning what doesn't work over and over until you get it right.

-If you don't know something, ask around. You'll never go into your first port job with all the answers. You'll figure out what you need to ask as you go.

 

-If nothing else, remember these 3 things: Be conservative, take your time, don't try to make your tools do something that you can't make them do/they shouldn't do.

-When you go over a new cylinder, take a carbide and lightly go across all of the surfaces to eat the paint away. It makes everything so much easier to see.

 

I know I missed a lot, but with as much as I wrote, I'm sure there were some typos and holes in explanation.

Edited May 6, 2014 by tfaith08

[Deadbeat]

post a link to the blasterforum thread, i would like to see what ken said about all this

[dirtydownunder]

Woah, woah woah !.

Or just pay some one to port ya cylinders.

[dirtydownunder]

Fukn , Mark Twain over here.

[BrokeVW]

I read it all.... I don't plan on porting anything, but I wanted to learn more about it.

It's a bit more involved than the porting and polishing I did on little nitromethane RC engines, I'll probably be leaving any Banshee porting to the pros.

 

Thanks for the informative post!
 

[trickedcarbine]

Gonna get interesting

[Coupelx]

In b4 da shit storm.

[VoOK]

[tfaith08]

post a link to the blasterforum thread, i would like to see what ken said about all this

 

I've tried to get KOR to post or reply, but he hasn't put anything up yet.  I think it's mostly because he did the videos a little while back and no one had anything to add. 

 

Stick to blasterforum

 

Say what?

[sstaton1983]

Interesting topic. i like Mac Dizzy"s site as well.

[tfaith08]

post a link to the blasterforum thread, i would like to see what ken said about all this

 

www.blasterforum.com/threads/porting-101.58962/

 

Let start off with that porting is the process of changing the the ports of the engine. It isn't the process in which an effort is made to fill the cylinders with as much air fuel mixture. 

When you port a cylinder, you are not trying to fill the cylinder with AFM, that would make for a big mess. When you port, you are changing the shape, size, and timing of the ports.

 

So we don't want more AFM? Or are you observing the potential for it to be taken in a different context, which you obviously discovered?

 

Sorry, I tried to make a contribution.  I've been porting cylinders since I was 16 and I just ported my 40th cylinder about a month ago.  This was an attempt at giving a guy that's completely new to porting somewhat of a glidepath because so many people are hell-bent on porting their cylinder and believe that they can do it with a file and a piece of scotchbrite.  They have no clue what they're doing, but they're enthusiastic about making power and they want to try.  I'm trying to give them an idea about what to do, but I'll refrain from future attempts because I just recently discovered that you don't actually want to fill your cylinders with the most AFM possible.  Can you believe that?

[sstaton1983]

Our Goal is more power, to make more power we need combustion, the more air and fuel shoved into the cylinder at the correct ratio makes the power...The style of the port job will tell us where in the rpm the power will be made. there are other variables like pipe scavenging effects to match the porting for full benefits. This sight needs more people that are interested pipe effects and what porting a cylinder actually does.. I like to learn in detail of how to make a more efficient motor.

[tfaith08]

Again, porting isn't the process in which an effort is made to fill the cylinder as much air fuel mixture as possible. 

Porting is just the process in which you modify the ports of an engine.

 

Which is in an attempt to ultimately do what?

 

What you're getting at is like saying that installing pipes won't make more power or create suction and the return pusle, nor will it vent the exhaust gasses at all.  Installing pipes is just unbolting some things and bolting them back in, installing the springs, and clamping the expansion chambers to the stingers.

Edited May 6, 2014 by tfaith08

[tfaith08]

No, by my logic, porting is a modification that is an attempt to fill the cylinders with the most possible AFM.  I'm pretty sure I stated that a few times already. 

 

But I'd like to ask you again, what does "changing the shape, height, and duration of the ports" (which is roughly what you posted) effectively amount to? 

[sstaton1983]

Let's not get hung up on the definition of porting and maybe discuss the theory.