TraditionalTool
Addicted to ArboristSite
Ok, I'm chilling with Jennings...interesting reading...I guess there is no real short cuts...
Porting 101
- Thread starter pepsifreak28
- Start date
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sawinredneck
Addicted to ArboristSite
TT IF you want to raise or lower all you are going to take out is .020-.040" THATS IT!!! Very litle changes make big changes in performance!
Concentrate on cleaning things up and making it flow.
What I was reffering to on the intake side is you want to widen it about as much or more than the exhaust side. Compare the two and you will better understand. Also you need to "bellmouth" for lack of a better word the inlet of the intake so you can make as much use of the air coming in, but leave enough srength. Think of it this way, all of the intake gases fill the intake tube, then meet that "wall" on the cylinder so they bunch up and swirl around. Your job is to make a smooth transition from the intake tube to the cylinder to the piston. Same with the exahsut, but there isn't as much to work with there.
Yes a "knife edge" is a good way to describe it, I like to leave them a bit more rounded just for strength myself.
Clean up the flashing and polish things up a bit then you can start to see and understand what more can be done. Don't be afraid of it, those cylinders are cheap experiance!
Concentrate on cleaning things up and making it flow.
What I was reffering to on the intake side is you want to widen it about as much or more than the exhaust side. Compare the two and you will better understand. Also you need to "bellmouth" for lack of a better word the inlet of the intake so you can make as much use of the air coming in, but leave enough srength. Think of it this way, all of the intake gases fill the intake tube, then meet that "wall" on the cylinder so they bunch up and swirl around. Your job is to make a smooth transition from the intake tube to the cylinder to the piston. Same with the exahsut, but there isn't as much to work with there.
Yes a "knife edge" is a good way to describe it, I like to leave them a bit more rounded just for strength myself.
Clean up the flashing and polish things up a bit then you can start to see and understand what more can be done. Don't be afraid of it, those cylinders are cheap experiance!
MS460WOODCHUCK
Addicted to ArboristSite
Do you have any pictures of these type of cylinders already ported?
TraditionalTool
Addicted to ArboristSite
So, that's less than 1/64th of an inch, right? That doesn't seem like much, and I think there are a lot of calculations at play here, The bellmouth you mention before will take it more than that. Just sayin', that in this case I think your talking about raising the roof of the port.
Yeah, that makes sense.
Ok, not too worried about the cylinder at this point, even took a file and needle nose and pulled the ring out of the bad piston. In theory I would reuse it by cleaning the ring slot and putting a new ring on it. Doesn't the ring matter mostly in how tight the compression is?
+1
sawinredneck
Addicted to ArboristSite
The crappy cell phone pics are in this thread:
http://www.arboristsite.com/showthread.php?t=40236&highlight=bubba
Deeper in the thread I go after it again, heres the post with pics: http://www.arboristsite.com/showpost.php?p=535390&postcount=90
Really a lot of information in that thread if you take the time to read and analyze it!
http://www.arboristsite.com/showthread.php?t=40236&highlight=bubba
Deeper in the thread I go after it again, heres the post with pics: http://www.arboristsite.com/showpost.php?p=535390&postcount=90
Really a lot of information in that thread if you take the time to read and analyze it!
pepsifreak28
ArboristSite Operative
Sorry I haven't been posting today anyways in porting the main thing is you got to give it a try and just clean up and improve the flow.. like redneck said its a learning process..
Understanding how a 2 stroke truly works is a key part I put the 2 stroke video at the first post so you can watch it until your eyes bleed lol
just because you know the basic operation of the 2 stroke don't mean anything if you watch the video over and over you start to see.... hey wait a minute.. if i do this or that i will get this result..
such as if you move the exhaust port closer to the spark plug you will get an effect of "spark then exhaust" very quickly giving you higher rpms.. but less torque..
and the further i move the exhaust port away from the spark plug i get a "spark wait wait wait then exhaust"
giving the fuel more time to expand and push down on the piston
and many other things factor in there as well like angle of the port and the duration of the time that the port is open etc etc but those are small effects that you wont notice as much as the other.
The main thing is at first to clean up the casting flaws and improve flow that will allow the engine to breathe I wish i could find a before and after of a ported jug but i was only able to find the ktm pics if anyone wants to show a before and after that would help a lot..
Understanding how a 2 stroke truly works is a key part I put the 2 stroke video at the first post so you can watch it until your eyes bleed lol
just because you know the basic operation of the 2 stroke don't mean anything if you watch the video over and over you start to see.... hey wait a minute.. if i do this or that i will get this result..
such as if you move the exhaust port closer to the spark plug you will get an effect of "spark then exhaust" very quickly giving you higher rpms.. but less torque..
and the further i move the exhaust port away from the spark plug i get a "spark wait wait wait then exhaust"
giving the fuel more time to expand and push down on the piston
and many other things factor in there as well like angle of the port and the duration of the time that the port is open etc etc but those are small effects that you wont notice as much as the other.
The main thing is at first to clean up the casting flaws and improve flow that will allow the engine to breathe I wish i could find a before and after of a ported jug but i was only able to find the ktm pics if anyone wants to show a before and after that would help a lot..
pepsifreak28
ArboristSite Operative
On a side note where is all the machinist/fabricators on the forum must be some out there that are handy with grinders and such I want a bold on reed for the little walbro carbs lol
J.W Younger
ass kissing impaired
Who was it said "a little knowlege is a dangerous thing"?
J.W Younger
ass kissing impaired
you're right, I did, but I'm not smart enough to come up with that on my own so I must have heard it before.
TraditionalTool
Addicted to ArboristSite
redneck,
I've read through it and the associated threads, and will go through it again, probably more than once.
Question on the external openings of the ports, where they are radiused/bellmouthed. That is just opened up and doesn't follow the guidelines of not opening but .020"-.040", right? Seems that as long as the inside of the port stays the same, the radius/bellmouth on the outside of the cylinder (what I'm referring to as the external portion of the port) should be softened to provide for the smooth air flow. At least if I understand correctly.
In regard to the inside of the cylinder though, that is mostly where the concerns are with the rings, raising the roof, lowering the bottom, etc...
I realize that each cylinder is different, but just thinking in general and in getting the external portions of the ports opened/softened so that the air will flow well.
And yes, your pics were lousy but I could tell what you were trying to show. Not to worry.
buck futter
ArboristSite Guru
here are some ideas,
what do you think pepsifreak and TT, would this run ok?
buck
what do you think pepsifreak and TT, would this run ok?
buck
TraditionalTool
Addicted to ArboristSite
BF,
That looks great to me. I see you seem to have raised the roof on the intake on the inside, but it looks great.
I was thinking to soften the edges on the intake, where the muffler attaches to the cylinder at the outside, but yours looks very clean and I suspect it should flow nicely. However, since you didn't widen it too much, it seems that the ring should have plenty of support.
Have you put this all together?
Several things I noticed here.
First you show raising the exhaust port. That is something I rarely do. This will cost you compression and torque. If you're after RPMs, you'll get them anyway with a good port job. I typically see about a 1500 RPM increase at WOT without raising the exhaust.
You show raising the intake as well. I'm not sure why you'd want to do this since the intake opens from the bottom up. If you want to increase intake duration, you do it by lowering the port and widening.
Be careful enlarging the transfers. Yes, they may flow more volume, but at the expense of velocity.
I always widen the ports; intake, exhaust, and transfers. If not, you're not really doing much of a port job. I shoot for intake and exhaust port widths of 70% of bore diameter. This is not always possible though. Sometimes you are limited by skirt width, ring end locations, etc. The transfers I widen and angle towards the intake. I usually raise them a couple of degrees as well, especially if I lowered the cylinder. If you're not comfortable messing with the transfers, then leave them alone. You'll see significant gains without changing them at all.
Port shape is extremely critical. The top and bottom of the exhaust port are most critical. The rings travel completely over it with every stroke. They need to be concave, not even flat. When done with port shape it's very important to put a bevel back on the top and bottom as well. This helps significantly in keeping the ring from snagging and destroying your work.
First you show raising the exhaust port. That is something I rarely do. This will cost you compression and torque. If you're after RPMs, you'll get them anyway with a good port job. I typically see about a 1500 RPM increase at WOT without raising the exhaust.
You show raising the intake as well. I'm not sure why you'd want to do this since the intake opens from the bottom up. If you want to increase intake duration, you do it by lowering the port and widening.
Be careful enlarging the transfers. Yes, they may flow more volume, but at the expense of velocity.
I always widen the ports; intake, exhaust, and transfers. If not, you're not really doing much of a port job. I shoot for intake and exhaust port widths of 70% of bore diameter. This is not always possible though. Sometimes you are limited by skirt width, ring end locations, etc. The transfers I widen and angle towards the intake. I usually raise them a couple of degrees as well, especially if I lowered the cylinder. If you're not comfortable messing with the transfers, then leave them alone. You'll see significant gains without changing them at all.
Port shape is extremely critical. The top and bottom of the exhaust port are most critical. The rings travel completely over it with every stroke. They need to be concave, not even flat. When done with port shape it's very important to put a bevel back on the top and bottom as well. This helps significantly in keeping the ring from snagging and destroying your work.
TraditionalTool
Addicted to ArboristSite
Brad,
Would love to see how you would go about porting this cylinder, is it possible for you to markup the images?
buck futter
ArboristSite Guru
TT,
yes it ran very well and has been for 2 years now.
I'm not going to say I know it all, I'll leave that for others to tell you.
You need to sift through the sand to get the nuggets of info.
yes it ran very well and has been for 2 years now.
I'm not going to say I know it all, I'll leave that for others to tell you.
You need to sift through the sand to get the nuggets of info.
Simply widen the intake and exhaust to 70% of bore diameter, or what ever the limitations of piston design will let you. I might also widen the transfer closest to the intake, bringing the back edge closer to the intake. I would only widen it as low as what the crown of the piston travels. Watch out for rings ends when widening transfers as well.
Don't raise or lower any ports at this point. You'll see huge gains with stock timing.
Don't make the carb side of the intake spigot any larger than the intake elbow.
Widen the muffler flange about as much as you widen it at the cylinder wall. Port match the muffler and gasket.
Install the cylinder without rings and measure squish. Then decide whether to use a gasket or not.
TraditionalTool
Addicted to ArboristSite
Thanks Brad, this seems to be a good rule of thumb to go by.
So, my bore is 44mm, and if I understand you correctly, your saying don't go beyond 30mm wide (30.8 is 70 percent).
Could you explain the skirt so I can determine if there is any conflict with widening it to 30mm? Edisto mentioned that if the piston has inlets for the crankshaft, that could present problems. I have the old piston out of the engine and can take pics or measure if something would help you to determine that.
Just remember that that is the length of the chord, not the circumference of the cylinder.
Hopefully a pic will help. I superimposed a port shape onto a piston. The recommendations I have seen are for 2 mm of skirt past the port (on either side) for a good seal. You can see that widening the port past the edges of the skirt would prevent any seal at all.
So just measure the (skirt width - 4mm), and 70% of the bore diameter, and go with the smallest of the 2.
70% as measured along the curve of the cylinder wall.
