Porting

[link]

Expert porting of chainsaws is worth every penny- for the satisfaction alone of pi**ing off the malcontents, Nancys, and Karens.

Owner satisfaction, increased performance, and higher productivity, are bonuses.

But it's a hit and miss game, not a quality standard.
A diesel engine surpass a gas engine in both torque and hours, why is that?
Relative low rpm does not make a pretty HP chart, only long lasting reliable engines.

 

[huskihl]

But it's a hit and miss game, not a quality standard.
A diesel engine surpass a gas engine in both torque and hours, why is that?
Relative low rpm does not make a pretty HP chart, only long lasting reliable engines.

There’s guys around who can port your saw and actually make it slower. You could look into that.

Longevity

 

[dmb2613]

I dont know She it from shanola about porting, but I do know a 034S will cut a circle around a 036 wink lol

 

[link]

There’s guys around who can port your saw and actually make it slower. You could look into that.

Longevity

I know you will make it better buddy. I just don't follow the popular tunes...

 

[ApePilot]

I know you will make it better buddy. I just don't follow the popular tunes...

Perhaps, link, you should go take a nice, warm bubble bath and let the adults discuss these things.

 

[ApePilot]

Hello, What I was meaning in my first post. Is that the burning mix ceratet a pulling effect in the cylinder vacuum, when the gases is leaving The cylinder out in the exhaust port. An then to the muffler.
A original muffler is restrectiv and Will not make a strong pull, But it wil help a little. A modded muffler Will help to get more pulling effekt. The muffler on the picture make a realy Strong pulling effect.
The Best exhaust system on a 2-stroke engine i a expensionchamber. It Will help pulling fuel from the crankcase and push back unburned fuel in the cylinder before the exhaust port close. But you need to have more blowdown on the engine. if you use a expensionchamber. Around 25-35 degrese. So the pipe gets time to work correct. My Hybrid have 30 degrese blowdown. regular muffler.
Here it is with pipe.

Seems to me, that divergent piped saw that you have pictured at the bottom of your post would need an extra long blowdown simply because the divergent-only pipe does create a low-pressure (suction) exhaust, but does nothing to push back the charge that it would exteract out of the cylinder along with the spent charge. That's why a tuned pipe requires a convergent cone as well, as you likely well know. A properly tuned pipe will allow the engine to respirate far better at the pipe's designed rpm's than without, but, if I understand the dynamics, the porting numbers for a tuned pipe doesn't change compared to a non-tuned exhaust.
What are your beliefs Bjorn?

 

[Bjorn T]

Seems to me, that divergent piped saw that you have pictured at the bottom of your post would need an extra long blowdown simply because the divergent-only pipe does create a low-pressure (suction) exhaust, but does nothing to push back the charge that it would exteract out of the cylinder along with the spent charge. That's why a tuned pipe requires a convergent cone as well, as you likely well know. A properly tuned pipe will allow the engine to respirate far better at the pipe's designed rpm's than without, but, if I understand the dynamics, the porting numbers for a tuned pipe doesn't change compared to a non-tuned exhaust.
What are your beliefs Bjorn?

Hello, I am not an expert. But if you port a cylinder for regular muffler or a tuned pipe. The porttiming numbers will be way different.

The big changes is blowdown.

 

[Bjorn T]

Seems to me, that divergent piped saw that you have pictured at the bottom of your post would need an extra long blowdown simply because the divergent-only pipe does create a low-pressure (suction) exhaust, but does nothing to push back the charge that it would exteract out of the cylinder along with the spent charge. That's why a tuned pipe requires a convergent cone as well, as you likely well know. A properly tuned pipe will allow the engine to respirate far better at the pipe's designed rpm's than without, but, if I understand the dynamics, the porting numbers for a tuned pipe doesn't change compared to a non-tuned exhaust.
What are your beliefs Bjorn?

Hello. I Can give you thre exampels, 1 Woods porting, with muffler. Exhaust widened to 65% of the Bore and 154 degrese of duration, intake widened and lowered so 160 dregrese of duration, transfers adjusted, size and aiming. 120 degrese of duration

2, with tuned pipe. Exhaust 60% of the Bore, 170 degrese of duration. Intake widened and lowered so 152 degrese of duration. Transfers adjusted size and aiming. 110 degres of duration. This Will give 30 degrese blowdown, and that Will give the pipe time to work correct.

3. race saw with pipe, exhaust same as number 2. Intake widened Max, as mutch as possible, depends on the piston skirt. Lowered to 170 degrese of duration. Full circle crank, to raise the crankcase compression. Transfers modified, opened and aimed for good flow, 110 degrese of duration and bigger carburator, this porting give you 30 degrese of blowdow, and 40 degrese of crankcase compression, good fore high rpm cut.

fore work saws I like 45-50 degrese of crankcase compression or more, that give you a snappy saw. And dont raise the exhaust more than 102 degrese, to have some tourque fore long bars.
this is just general porting Numbers. And it Will not be perfect on all saws. Mostley because there is many different modells of transferports.

 

[Lightning Performance]

There’s guys around who can port your saw and actually make it slower. You could look into that.

Longevity

So your known for making them fast, yes?... sooo how slow can you make my saw? I need it to last until the next millenia, please

 

[Bjorn T]

So your known for making them fast, yes?... sooo how slow can you make my saw? I need it to last until the next millenia, please

This Will work good. https://www.videoman.gr/sv/44237

 

[huskihl]

This Will work good. https://www.videoman.gr/sv/44237

Not really known for anything. I just show the way it was vs the way it is now I guess

 

[ApePilot]

Hello, I am not an expert. But if you port a cylinder for regular muffler or a tuned pipe. The porttiming numbers will be way different.

The big changes is blowdown.

I'm going to have to disagree with that statement. The tuned pipe is tuned to the porting, not the other way around. Obviously, there would be advantages to optimizing both the porting and the pipe to each other, but the porting numbers would still be not much different. Take a look at the Radne Raket 120 kart engine. It is exactly derived from the Husqvarna 3120xp. Same OEM piston, same OEM crank, same OEM cylinder, same ignition timing (which should actually be ******** for better high-rpm torque). The only real differences to the 3120xp saw is a redesigned heavier-duty crankcase to facilitate bolting the engine to a frame, the clutch sprocket, and the tuned pipe. It develops 14 hp at 9000 rpm compared to a stock 3120xp saw of 8 hp at 10,000 -- all because of the tuned pipe, nothing more.

 

[Bjorn T]

I'm going to have to disagree with that statement. The tuned pipe is tuned to the porting, not the other way around. Obviously, there would be advantages to optimizing both the porting and the pipe to each other, but the porting numbers would still be not much different. Take a look at the Radne Raket 120 kart engine. It is exactly derived from the Husqvarna 3120xp. Same OEM piston, same OEM crank, same OEM cylinder, same ignition timing (which should actually be ******** for better high-rpm torque). The only real differences to the 3120xp saw is a redesigned heavier-duty crankcase to facilitate bolting the engine to a frame, the clutch sprocket, and the tuned pipe. It develops 14 hp at 9000 rpm compared to a stock 3120xp saw of 8 hp at 10,000 -- all because of the tuned pipe, nothing more.

Hello. There are many ways to porting and building pipes. If you have 10 porters and 10 Pipe builders. To build 10 saws of the same modell. None Of the saws Will be exaktly the same.

most Factory build 2-stoke high performance engines, like dirt bikes have a blowdown of 30-35 degrese. If some smart guy have been able to build a pipe for short blowdown. And make many HP extra, thats a big bonus. But my head or calculation programs on the internet, is not smart enought to do it.

 

[ApePilot]

most Factory build 2-stoke high performance engines, like dirt bikes have a blowdown of 30-35 degrese. If some smart guy have been able to build a pipe for short blowdown. And make many HP extra, thats a big bonus. But my head or calculation programs on the internet, is not smart enought to do it.

Any shorter of blowdown, and the spent charge will be pushed into the transfers and down into the case. I've seen the results of this.... black spooge in the case and spitting out the carb. You can't generate a negative pressure wave immediately after the exhaust port begins to open. It takes a few msec for that negative wave to get back to the exhaust port and help suck the exhaust and some of the fresh charge out. Therefore, you have to time the blowdown for the expected rpms to achieve and for the negative pressure wave to return to help suck the fresh charge up from the case. The greater the rpm's the longer (in degrees) the blowdown should be. If the transfers opened too early, like you are suggesting, there would be a flow reversal within the transfers that would take even more time to correct and the transfer flow efficiency would be squandered away. There's a reason most of today's 2T bikes have power valves.... it's to increase the blowdown time as rpm's rise to help match the return negative pressure wave of the pipe to allow for a larger range of rpm's that the pipe can be in tune with.
Even without a tuned pipe, blowdown should be matched to the desired rpm range, IE, the higher the rpm, the longer the blowdown should be. If you're raising the transfers in relation to the exhaust roof, you're then limiting the upper rpm range of power. You have to allow the exhaust to evacuate and allow enough time for combustion chamber pressure reduction before you open the transfers.
The only reason I can think for raising the transfers in relation to the exhaust port is to achieve low rpm torque, but that is exactly opposite of what a 2T is best used for, unless you merely like a throttle-snappy saw that peters-out just above mid-range. That would be a waste of displacement and saw mass.

The big question in my mind, is what would appreciably increasing a stock piston ported intake duration actually accomplish? Would it help Mid-range torque? Higher rpm torque? There would be a point at which any larger a duration would reduce primary compression. I'm guessing that the name of the game is to help cram as much fresh charge as possible into the case, and the momentum of the incoming charge from the carb would continue into the case even after a positive pressure is achieved, at a certain rpm range at least. Below that range, the extra duration may not be a benefit. Does this sound about right?

I think we have a good productive discussion going now.

 

[huskihl]

Any shorter of blowdown, and the spent charge will be pushed into the transfers and down into the case. I've seen the results of this.... black spooge in the case and spitting out the carb. You can't generate a negative pressure wave immediately after the exhaust port begins to open. It takes a few msec for that negative wave to get back to the exhaust port and help suck the exhaust and some of the fresh charge out. Therefore, you have to time the blowdown for the expected rpms to achieve and for the negative pressure wave to return to help suck the fresh charge up from the case. The greater the rpm's the longer (in degrees) the blowdown should be. If the transfers opened too early, like you are suggesting, there would be a flow reversal within the transfers that would take even more time to correct and the transfer flow efficiency would be squandered away. There's a reason most of today's 2T bikes have power valves.... it's to increase the blowdown time as rpm's rise to help match the return negative pressure wave of the pipe to allow for a larger range of rpm's that the pipe can be in tune with.
Even without a tuned pipe, blowdown should be matched to the desired rpm range, IE, the higher the rpm, the longer the blowdown should be. If you're raising the transfers in relation to the exhaust roof, you're then limiting the upper rpm range of power. You have to allow the exhaust to evacuate and allow enough time for combustion chamber pressure reduction before you open the transfers.
The only reason I can think for raising the transfers in relation to the exhaust port is to achieve low rpm torque, but that is exactly opposite of what a 2T is best used for, unless you merely like a throttle-snappy saw that peters-out just above mid-range. That would be a waste of displacement and saw mass.

The big question in my mind, is what would appreciably increasing a stock piston ported intake duration actually accomplish? Would it help Mid-range torque? Higher rpm torque? There would be a point at which any larger a duration would reduce primary compression. I'm guessing that the name of the game is to help cram as much fresh charge as possible into the case, and the momentum of the incoming charge from the carb would continue into the case even after a positive pressure is achieved, at a certain rpm range at least. Below that range, the extra duration may not be a benefit. Does this sound about right?

I think we have a good productive discussion going now.

Most of that might sound good to you or look good on paper, but doesn’t work well in a saw with a can muffler.

Most piped race saws have 26-32° blowdown, where muffler race saws are more like 24-28°. Woods ported saws need torque so the exhaust is typically lower, and raising the transfers after lathe work adds more torque yet, resulting in higher rpm while cutting. Some saws I’ve had luck adding a few degrees blowdown and some run the best for me with 6-8° less.

There’s no one-recipe-fits-all type stuff. And very little of the stuff written about piped motorcycles works in a saw. Bore/stroke ratio is too different

 

[ApePilot]

Most of that might sound good to you or look good on paper, but doesn’t work well in a saw with a can muffler.

Most piped race saws have 26-32° blowdown, where muffler race saws are more like 24-28°. Woods ported saws need torque so the exhaust is typically lower, and raising the transfers after lathe work adds more torque yet, resulting in higher rpm while cutting. Some saws I’ve had luck adding a few degrees blowdown and some run the best for me with 6-8° less.

There’s no one-recipe-fits-all type stuff. And very little of the stuff written about piped motorcycles works in a saw. Bore/stroke ratio is too different

I now understand where you're coming from, I think. It makes more sense now than when you previously indicated that you raise the transfers but didn't provide a description of the resultant relative blowdown.

My 3120 currently is set up as:
Blowdown: 19.6 deg
Exhaust duration: 164.02 deg, opens at 97.991 deg atdc
Transfer duration: 124.79 deg, opens at 117.6 deg atdc
Intake duration: 135.8 deg, closes at 67.88 deg atdc
true compressible volume: 86.207 cc
compressed volume: 9.64 cc
squish: 0.58mm
Compression ratio: 8.943:1

-- it could likely use more blowdown, but I'm unwilling at this point to reduce it's displacement (raising the exhaust roof) to increase blowdown time. But perhaps it wouldn't hurt.
Blowdown would be longer if Transfer duration was reduced to 120 deg ( for a 22 deg blowdown) but I'm hesitant about using epoxy-fill, likely not a reliable option.

However, it's current intake duration is anemically short (135.8 deg.) compared to others' figures. It probably should be opened up to around 140 deg or possibly more. But I'd like to better understand what advantages a longer intake duration would provide.

 

[link]

Perhaps, link, you should go take a nice, warm bubble bath and let the adults discuss these things.

Hehe... just outta curiosity - how old are you buddy?
I would love a nice bubble bath though - I guess I'd have to make it happen myself...

 

[Lightning Performance]

I now understand where you're coming from, I think. It makes more sense now than when you previously indicated that you raise the transfers but didn't provide a description of the resultant relative blowdown.

My 3120 currently is set up as:
Blowdown: 19.6 deg
Exhaust duration: 164.02 deg, opens at 97.991 deg atdc
Transfer duration: 124.79 deg, opens at 117.6 deg atdc
Intake duration: 135.8 deg, closes at 67.88 deg atdc
true compressible volume: 86.207 cc
compressed volume: 9.64 cc
squish: 0.58mm
Compression ratio: 8.943:1

-- it could likely use more blowdown, but I'm unwilling at this point to reduce it's displacement (raising the exhaust roof) to increase blowdown time. But perhaps it wouldn't hurt.
Blowdown would be longer if Transfer duration was reduced to 120 deg ( for a 22 deg blowdown) but I'm hesitant about using epoxy-fill, likely not a reliable option.

However, it's current intake duration is anemically short (135.8 deg.) compared to others' figures. It probably should be opened up to around 140 deg or possibly more. But I'd like to better understand what advantages a longer intake duration would provide.

It appears your quoting known measurements for online calculators not a degree wheel. Am I correct?
If so this very well may or may not match the inside of your acual cylinder.