Porting 101

I would like to start a sticky for porting...
I see a lot of people asking questions about porting..
feel free to add to this thread all you fellow modders..

first things first here you got to understand how 2 stroke engines operate just because you know the basics dont mean nothing here is a basic video of a two stroke..


http://www.youtube.com/watch?v=LuCUmQ9FxMU


once you understand the basic idea of it watch the video again..and think about how you can improve its operation..


if you thought by getting air/fuel mixtured burned and out of the engine you guessed right..

Okies now that you got that down we can move onto some more advanced stuff..

the first thing to porting and engine just the basic "improvements" most mass production engines are cast from molds so you will find casting flaws and such all thoughout the bore/jug removeing them will increase flow a lot.. meaning more air/fuel moveing though the engine more fuel and air yay! we want more air and fuel moveing though the engine.

there are other ways we can improve though so we are going to look into what else can we do to make more air/fuel move though the engine better?
I know lets wideing those openings a little! since we got some extra metal around the openings..

so now you got your jug from your chainsaw you can see in from the bottom end though the exhaust opening/port and though the intake where the carb flows into it..
looking all around the inside your looking for more ways to get more air/fuel into the engine so lets follow the flow of combustion first thing the engine does is sucks fuel/air in though the carb and into the crankcase..

then into the crankcase where it is forced up though the passageways around the piston and into the combustion area..


then its compressed and ignighted and then out the exhaust pipe...

Here ya go. LINK. LINK

now once you see the flow of things you can begin to improve on somethings removeing those casting flaws and widening some of the ports and allowing more air and fuel to flow though the engine

here is some pics of a ported 2 stroke dirt bike engine up close and personal

Keep it at beginner level

You have a good start, keep it going. There is a lot of porting info out there but it goes from beginner to more advanced to quickly for me.

In this picture you can see the crankcase to combustion chamber transfer ports if you notice they have been filed/ground to improve flow and to a nice edge and widened a little as well doing this will alow more air and fuel to flow easyier into the combustion chamber

In this picture you can see the exhaust port the circle is more than likely around where it use to be stock
notice the new oval shape its kind of shaped like a folded funnel

When you start to port your engine the first thing to do is look inside the jug and at all the ports and see how you can improve the flow of air and fuel you should start to notice casting flaws and extra metal here and there
I like to use a locksmith file set on weed eaters and small engines its easyier to get a file in then it is a dremel plus you dont take as much metal off as fast a chainsaw chain file works great too

The more advanced stuff will come in time the main goal for now is to just improve the flow without going overboard a little improvment will go a long way faster throttle response and better performance overall there is some risk to porting that you should take note off if you take metal from the bottom of the exhaust port to much will allow free porting that means your piston travels to tdc it exposes the exhaust port to the crankcase bad idea that will allow the fuel/air mixture to vent into the exhaust and not into the combustion area though the transfer ports..

also some other risk are DONT GO OVERBOARD! sometimes and it has happened to be before is you grind to much and expose an air leak this happens a lot on the transfer ports if you dont make to big of a hole you can fix it with jb weld or epoxy but we dont wanna go to far so make sure you got the metal on the outside of the jug to grind..


here is anouther risk that often takes place in porting when you widen ports dont forget the rings there your friend they half to travel over those ports many times
if you go to wide your piston ring can pop out into the port and snag it snap the ring and its not a pretty site ....


there is other risk as allways but when you start to "clean up" the casting flaws and improveing flow you will start to see about how far you can take something dont get greedy with porting a little can improve a lot the exhaust port alone can make a big difference as you noticed with the muffler mods..

I'm not the best picture drawer so bear with me in this picture you can see the basic idea of the engine the green parts is where the fuel and air is I like to pack as much fuel and air in this area as i can so improveing flow into here is a big improvement i see a lot of weed wackers and some chainsaws that could really improve in the intake area as well as exhaust i notice a lot of small engines that have a very short intake duration (meaning how long the port window is open) and short exhaust duration if you lower the intake port a little(dont go overboard here as you need some closed time)the closed time is the time its pushing the fuel air mixture into the combustion chamber if you didnt have a closed time it would spray fuel out the carb and not into the transfer ports into the combustion chamber when you get into duration and such the main thing is to watch the video at the very top or watch basic 2 stroke operation and think in your head of the rhythm of the engine makes me think of those old hit and miss engines take that rhythm and go look at your chainsaw engine crank it around a few times by hand and watch how the ports open and close you should see a rhythm now as your watching the ports open and close realtive to the piston travels the faster the ports open and close the more rpm you get or the distance from the intake to the exhaust somewhat like intake exhaust intake exhaust intake exhaust intake exhaust if you have some distance between the ports you will get a rhythm like intake space exhaust intake space exhaust intake space exhaust member there is a little time between the intake and exhaust stroke to allow the fuel to be pushed from the crankcase into the combustion area so rhythm is the duration of the port window and the timeing this is on piston ported engines where the duration really matters thats why on dirt bikes they use reed valves if you really mess up in the intake area you will half to make a reed cage and thats not a bad thing if you was to make a reed cage and put reeds on your saw but im not sure if you would be able to put the plastic parts back on anyways the main thing to reamember is when messing with the intake side of things improveing flow is a good thing but watching the duration as well you got to have that moment where its closed to allow the pistons downward movement to push the air and fuel into the transfer ports into the combustion chamber we wouldnt half to worry about this is we had a reed cage if there is some people in the forum that can make some reed cages for chainsaws i would buy one the reed cage is awesome imo because as soon as that piston starts going down it closes and you get almost the entire downward pressure of the piston to pack all the air and fuel into the combustion area meaning you can open your intake as far as you like allmost anyways back to the piston ported engine so when working on the intake side just reamember there has to be some time in there to allow the piston to push the fuel and air into the transfers into the combustion area so just watch the rhythm of your engine and think of it like a song in your head the best i can decribe it is with a tune

now the exhaust side the exhaust side is critical in one area the bottom of the port you go to far and you get free porting free porting is when the piston is at tdc it exposes the crankcase to the exhaust bad thing so be careful on the bottom now onto the details the exhaust port can be improved by widening getting all those burnt fuel out better improves things as far as exhaust goes the closer the port goes to tdc you will get a tingy high reving rpm engine with less torque the lower the port is to tdc the more torque you get the reason that is the fuel that is burning is expanding so the longer you hold the expanding gasses the more power you get from it the faster you ignight the fuel and release it out the exhaust pipe the less power you get from the charge so you get higher rpm the faster the fuel explodes and out the pipe the more you hold it in the higher the buzz j/k the higher the torque so in basics...

higher the port is to tdc =higher rpms
the lower the port is to tdc = more torque

note: when i say lower thats not grinding the bottom of the port

in modern 2 stroke dirt bikes if you ever rode the water cooled insane hell of a ride dirt bikes you will notice when you first start moveing you dont got high reving engine but when you get into the throttle a little you notice a drastic change in the bike it about throws you off like the engine woke up! how that works is what are called power valves its basicly a plate that is on the roof of the exhaust port that drops down on slower take offs and raises as the engine picks up rpms so it drasticly changes the duration and opens up the port to allow the rpms to increase so in a chainsaw if you wanted more torque you would need to add metal to the top of the port.

one thing to remember is that the engineers made the engine for the job.. you wouldnt want a high rpm engine on a chainsaw and you wouldnt want a high torque engine on a go cart so the engineers made the engine for its purpose I have seen guys that have gotten porting done and they think OHH! high rpms that sounds good so they get the porting done for high rpms but when you get high rpms you almost forget that you need some torque too its all basicly what you wanna do with the engine with chainsaws if you had high rpm would the bar and chain hold the higher rpm? or would it fly off so think about what you want from the engine if you had higher torque would it break the chains? or would it dull it fast take everything into consideration but for you beginners on the forum start with improveing the flow weed wackers in many areas you can find them in the trash some ryobi and stihl weed eaters have a reed cage if you get one of those you can really mod and tinker with it and not worry to much about messing it up beyond it being able to be used as weed wackers or trimmers you can sway with high rpm or high torque and it will still work it dont take much to cut grass.


please let me know if i missed anything blsnelling is a very good advanced porter i mainly wanted to explain the basics
there is a lot of porting going on in all areas of 2 strokes

you have the rc boaters/aircraft
dirt bike/four wheeler/carting/snowmobile/jet ski
chainsaw/weedwacker
almost all of them mod 2 stroke engines
for different tasks and raceing

I will try and keep adding to this thread as i find more pictures and websites feel free to add your pictures.

Great thread guys! Have read most of this already but nice having it in one place to reference. One thing I do not see enough of is examples of the tools needed/used to do the detailed work. Myself and others use carbide dremel bits for the ruff work, and various gritt sanding balls for the chamfer and cleanup. Have not yet figured out how to down size my pics or I would post what I use.

This is your post:

tomtrees58 said:

your rails are blue oil problem or you do not used bar oil we have a bar rail grinder its excellent but we have 35 sthil saws for you by a new bar tom trees

Click to expand...

This is your post on crystal meth:

pepsifreak28 said:

I'm not the best picture drawer so bear with me in this picture you can see the basic idea of the engine the green parts is where the fuel and air is I like to pack as much fuel and air in this area as i can so improveing flow into here is a big improvement i see a lot of weed wackers and some chainsaws that could really improve in the intake area as well as exhaust i notice a lot of small engines that have a very short intake duration (meaning how long the port window is open) and short exhaust duration if you lower the intake port a little(dont go overboard here as you need some closed time)the closed time is the time its pushing the fuel air mixture into the combustion chamber if you didnt have a closed time it would spray fuel out the carb and not into the transfer ports into the combustion chamber when you get into duration and such the main thing is to watch the video at the very top or watch basic 2 stroke operation and think in your head of the rhythm of the engine makes me think of those old hit and miss engines take that rhythm and go look at your chainsaw engine crank it around a few times by hand and watch how the ports open and close you should see a rhythm now as your watching the ports open and close realtive to the piston travels the faster the ports open and close the more rpm you get or the distance from the intake to the exhaust somewhat like intake exhaust intake exhaust intake exhaust intake exhaust if you have some distance between the ports you will get a rhythm like intake space exhaust intake space exhaust intake space exhaust member there is a little time between the intake and exhaust stroke to allow the fuel to be pushed from the crankcase into the combustion area so rhythm is the duration of the port window and the timeing this is on piston ported engines where the duration really matters thats why on dirt bikes they use reed valves if you really mess up in the intake area you will half to make a reed cage and thats not a bad thing if you was to make a reed cage and put reeds on your saw but im not sure if you would be able to put the plastic parts back on anyways the main thing to reamember is when messing with the intake side of things improveing flow is a good thing but watching the duration as well you got to have that moment where its closed to allow the pistons downward movement to push the air and fuel into the transfer ports into the combustion chamber we wouldnt half to worry about this is we had a reed cage if there is some people in the forum that can make some reed cages for chainsaws i would buy one the reed cage is awesome imo because as soon as that piston starts going down it closes and you get almost the entire downward pressure of the piston to pack all the air and fuel into the combustion area meaning you can open your intake as far as you like allmost anyways back to the piston ported engine so when working on the intake side just reamember there has to be some time in there to allow the piston to push the fuel and air into the transfers into the combustion area so just watch the rhythm of your engine and think of it like a song in your head the best i can decribe it is with a tune

Click to expand...

Any questions?

edisto said:

This is your post:



This is your post on crystal meth:



Any questions?

Click to expand...

This made my day.


Mr. HE

pepsifreak, just from skimming through your posts there seems to be a wealth of information. If you could break your posts into sentences and paragraphs it would make that information more accessible and understandable.

Keep up the good work.


Mr. HE

edisto said:

This is your post:



This is your post on crystal meth:



Any questions?

Click to expand...

Say what you will about Tomtree's posts ,however undecipherable ,the man does some uber gnarly tree work.....his pictures are much better

Pepsifreak,don't let these guys run you off.....they're gonna poke atcha but it's par for the course posting here

Addressing your composition....edisto is not far off,run-on sentences are seemingly incoherent and very difficult to follow.

Slow it down a little,break it into sub-topics and bring it mang.....then everyone will be able to appreciate what you have to offer

lol

Sorry about all that I wrote it on a half working laptop in a hurry and I am horrid with writing and explaining things. I do my best but I am willing to help share knowledge the best I can if you or someone would like to rewrite it ,add to it ,redo the pictures feel free I won't be upset or mad just wanted to help explain things with porting and the do and don'ts let me know if you would like to resize the pictures or make them better sent me a private message and ill edit the post ..

pepsifreak28 said:

Sorry about all that I wrote it on a half working laptop in a hurry and I am horrid with writing and explaining things. I do my best but I am willing to help share knowledge the best I can if you or someone would like to rewrite it ,add to it ,redo the pictures feel free I won't be upset or mad just wanted to help explain things with porting and the do and don'ts let me know if you would like to resize the pictures or make them better sent me a private message and ill edit the post ..

Click to expand...

I'm watching and have some Qs, but more so in regard to my specific cylinder, and how to evaluate it.

pepsifreak28 said:

In this picture you can see the exhaust port the circle is more than likely around where it use to be stock
notice the new oval shape its kind of shaped like a folded funnel

Click to expand...

I have seen others show that shape also, so that is obviously what works. In general is the concept to keep the top and bottom the same and elongate the smashed funnel shape as you show here?

Also, another thing I was wondering is that if you leave the opening top/bottom of the port the same, do you try and hollow/expand it out behind the cylinder also?

Thanks for sharing, I am one of the folks that is wanting to learn, and I appreciate the time you've taken, don't worry about your formatting of the content, the pics are fine, and just try to hit the enter key a couple times now and then, a little white space would help, but don't let that stop you from posting.

Can you offer some advice on how you would approach this cylinder?

Like how far you would take the funnel shape out to the sides, or any info like that would be helpful. What about the fins on the sides also?

Yes, yes, I know I need to clean it up with muriatic acid...

Intake:



Exhaust: