Porting 101

[whitebutler]

Yep, still talking about the saw and yes it sucks when she steps on my foot because I have to buy new caulks every time

 

[pepsifreak28]

I'm still around..

I'm still around and I'm really impressed at all you guys and all the pictures!
I haven't been able to do much on here as much as I would like.
With family problems and trying to get some land situated to build a cabin on has kept me away but I am still kicking and still chainsawing.
Keep up the good work you guys your doing great nice to see people not be afraid to experiment and tinker.

 

[Chesterewers]

porting okay for wood cutting saws?

That bit would be fine files even drill bits work too anything that will grind the metal.
The jug isn't that hard of a metal the coating isn't super hard either you would be suprised how fast you can take metal down with just a round chain file.

Hi I have a question, is porting okay for wood cutting saws? The video by the chainsaw guy on porting when he is done he said its for competition only not wood cutting. So how much porting can be done on a work saw? Is there anything wrong with getting maximum power from the saw by porting or should it be limited to avoid any potential problems? What problems can a ported saw have and how do we avoid them? Basicly is porting okay safe to do for our wood cutting tool.

 

[Terry Syd]

Just like a car engine, you can change the valve timing (and other aspects of the engine) to do whatever the job the engine is going to be used for. Do you want to pull a trailer or do you want to drag race with it - it's the same idea.

Most guys are happy just to get a little bit more out of what they have (eg, widening the ports). However, some of us 'petrol heads' can't leave any component of the engine alone and have to tweak everything. (I just discovered another way to get a bit more flow from my strato ports, its probably only going to be worth less than 2% more power, but I can't stop myself from doing it!)

 

[Chesterewers]

Just like a car engine, you can change the valve timing (and other aspects of the engine) to do whatever the job the engine is going to be used for. Do you want to pull a trailer or do you want to drag race with it - it's the same idea.

Most guys are happy just to get a little bit more out of what they have (eg, widening the ports). However, some of us 'petrol heads' can't leave any component of the engine alone and have to tweak everything. (I just discovered another way to get a bit more flow from my strato ports, its probably only going to be worth less than 2% more power, but I can't stop myself from doing it!)

its a 372 xp I want it for big cuts, I have a habit of keeping the throttle wide open, so I would just like to tweak it for more torq, it seems fast enough as long as the chain is sharp,

 

[huskydave]

Well I have done a few now and this is what I think. Everyone that can tune a carb should do some kind of muffler mod and richen up the carb a bit, gut your muffler add a small 1/2" hole or slightly bigger depending on the model and retune a bit richer. If you want to start porting saws and doing other things talk to an expert with that saw. If you start playing with the port timing your saw will almost always lose low end torque and gain higher rpm on full throttle this is because it spools up quicker and starts hitting highrpms quickly, to make up for this guys start using racechains that take up to 10 hours to sharpen properly and They won't give you any of their secrets readily. The intake and exhaust ports on most saws are rough and casted just by removing the cylinder and cleaning up the casting flaws you will notice an improvement. Widening the ports will give you more power without sacrificing torque but there is a limit to how wide yo can go depending on how wide the piston is and the model of saw and the work must be chamfered into the cylinder as to not snag a ring. I started out on a cheap saw that I paid 50.00 for and then started experimenting and asking a lot of questions slowly to give the experienced guys a chance to respond.

 

[Terry Syd]

Assuming you have already done the easy stuff like widen the exhaust and intake port, then there are two other ways to increase the torque. First, is raise the compression ratio - you know, remove the gasket under the jug and reduce the squish. That will raise the torque over the entire working powerband.

The second requires some work on increasing the time/area of the transfer ports. The increased transfer flow will drop the point of maximum delivery to the cylinder (max torque) lower in the powerband. The useable powerband will be broader. However, you may only need a little bit wider, bigger is not always better. The best way to do that is to widen the transfer ports rather than raise them. That takes quality tools to do and a skilled hand to use them.

If you've never done any porting before, you might see if you can find someone that does such work and tell him what you want.

 

[Terry Syd]

As far as changing port timing, I suggest that anyone starting out to use old pistons to try changing the timing - not the jug.

You can take .5mm off the edge of the piston next to the transfer ports to see if the extra transfer time/area is the direction you want the powerband to go.

Likewise, instead of just accepting some number, say 18 degrees of blowdown, as the magic number, just trim the edge of the old piston next to the exhaust port and find your magic number. It is far more informative to take it up in steps to see how it changes your powerband. If 16 degrees gives you a nice fat powerband that gets better as you load the saw, you will probably be glad you didn't carve up the jug for 18 degrees of blowdown.

If you don't have an old piston to carve up, a new piston isn't that expensive - and it gives you an excuse to freshen up the old girl with a new piston and ring/s after you find the timing you want.

 

[AUSSIE1]

With your 372, widen the exhaust and inlet to within 1.5mm of the piston skirt, remove the base gasket, muffler mod and retune.

This will give you more torque, not loose it.

This is a good way to start out and you will be surprised how well it will run.

There is alot more you can do further down the road as you can see if needs be.

 

[Chesterewers]

Only do the roof of the exhaust and floor of the inlet.
Leave just a very slight bevel. You don't need much.
A large bevel acts a bit like increased timing anyway.

hi how is wood cutting in Australia? On porting timing inlet moved up and exhaust down how far? I was trying to stay .015 of an inch or .38mm, if I go greater than that number twice as much or more is it too much or still within parameters for a work saw?

 

[Chesterewers]

cleaning

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

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:

how do you clean up everything with muriatic acid?

 

[CedarRock]

Glad to see this thread again.
I have been building a 066/660 with a bunch of saws I acquired. Bought a big bore and whittled on it a little..mostly polishing and opening up the transfers. Compared to the 460 big bore this one has very large ports. Don't know how much more to open and change dimensions..I haven't seen many posts on big bore porting.

 

[AUSSIE1]

hi how is wood cutting in Australia? On porting timing inlet moved up and exhaust down how far? I was trying to stay .015 of an inch or .38mm, if I go greater than that number twice as much or more is it too much or still within parameters for a work saw?

We have pretty hard woods which can be testing on saws but wouldn't have it any other way.

It's exhaust up, inlet down. Timing is measured in degree's. There is a heap of threads through the search function you need to study prior to tackling porting.

Glad to see this thread again.
I have been building a 066/660 with a bunch of saws I acquired. Bought a big bore and whittled on it a little..mostly polishing and opening up the transfers. Compared to the 460 big bore this one has very large ports. Don't know how much more to open and change dimensions..I haven't seen many posts on big bore porting.

You can open up your port up to 65% of the bore.

 

[timberwolf]

Originally Posted by CedarRock
Glad to see this thread again.
I have been building a 066/660 with a bunch of saws I acquired. Bought a big bore and whittled on it a little..mostly polishing and opening up the transfers. Compared to the 460 big bore this one has very large ports. Don't know how much more to open and change dimensions..I haven't seen many posts on big bore porting.

You can open up your port up to 65% of the bore.

On 066 you realy cant go 65% of bore on intake or exhaust width. With BB skirt is 35mm on a 56mm bore thats only 62.5% right to the skirt edge. on 660 with newer style piston skirt is only 34mm so limited to 63% to the skirt edge.

 

[CedarRock]

On 066 you realy cant go 65% of bore on intake or exhaust width. With BB skirt is 35mm on a 56mm bore thats only 62.5% right to the skirt edge. on 660 with newer style piston skirt is only 34mm so limited to 63% to the skirt edge.

63%..is that total space of intake and exhaust? How far can you safely go for squish? Right now its .017 without a gasket.

" bore on intake OR exhaust " I see that now..

 

[kmcinms]

Finally made up a nice degree wheel holder today. Was getting real tired of the crappy mount I half arsed together, and it never ran true which will throw off your measurement. Here are a few pics I think its pretty self explanatory.

That's awesome

 

[timberwolf]

63%..is that total space of intake and exhaust? How far can you safely go for squish? Right now its .017 without a gasket.

63% is the width of the skirt in relationship to the diamiter of the bore.

If the skirt was wide enough 65% is a good number and can go as high as 70% on exhaust if pushing for highest performance. Intake can go even higher if the rings don't cross into it.

I don't bother running squish any amount less than 0.020 in esp on 80cc plus engines, on a smaller saws depending on the shape of the head and squish band it can be run a little less.

 

[kmcinms]

TW, what comp. ratio is good for a 50cc saw running pump gas, woods port, and a muffler mod with stock port timing? And, altered port timing?

 

[Brian13]

Might be a dumb question, but I see this in just about every porting thread and I not sure what it is referring to. So what is blowdown? I have figured out it has something to do with exhaust but that is about it. Thanks.

 

[blsnelling]

Blowdown is the time in degrees, starting when the exhaust just starts to open, until the transfers just start to open.