From the testimonials I have read the 346 has a bit more than the 2149 when both are stock. When tuned and when all things are equal its pretty much a dead heat.
Husky 346XP vs. Jons 2149
- Thread starter bwalker
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dbabcock
Hi Tech Redneck
That's correct. My 2149 and Gypo's (later RB's) 346 cut virtually the same after Dennis modified them. Don't know how they cut stock. Dennis would probably know this. The two saws share many of the same parts, including the crankshaft assy. The cylinders are different in that the 2149 has a slightly larger bore and open transfer ports to the 346's closed transfers. Closed transfers cost more to make and theoretically make more power, so this may be the reason that the 346 performs better stock. After "woods" mods, however, they're even-up. The 2149 is also less money and both are made on the same production line.
oops
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oop #2
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closed transfers cost more to make and theoretically make more power, so this may be the reason that the 346 performs better stock.
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In theory a open transfer cylinder will wear faster than a closed port model. The reason for this is the fact that the open transfer cylinder has less bearing area than the same cylinder with closed ports. I bet thats why you do not see many open port high end saws today.
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closed transfers cost more to make and theoretically make more power, so this may be the reason that the 346 performs better stock.
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In theory a open transfer cylinder will wear faster than a closed port model. The reason for this is the fact that the open transfer cylinder has less bearing area than the same cylinder with closed ports. I bet thats why you do not see many open port high end saws today.
dbabcock
Hi Tech Redneck
BW,
Forgive me for my lack of understanding here, but are you refering to the amount of casting thickness in the cylinder wall between the bore and the transfer channel or the actual port width that the piston ring has to ride over?
Thanks.
Forgive me for my lack of understanding here, but are you refering to the amount of casting thickness in the cylinder wall between the bore and the transfer channel or the actual port width that the piston ring has to ride over?
Thanks.
I am reffering to area of the port as a percentage of the entire cylinder surface. The more area taken up by ports the less area the piston rings have to ride on which increases load on the cylinder and in theory will result in a shorter service life for the rings and cylinder.
dbabcock
Hi Tech Redneck
Thanks. That makes sense.
eyolf
Addicted to ArboristSite
BWalker says:
I don't really know if you're right or wrong, but I do happen to have a Jonsered 670 jug and one from a Husky 268 on the bench at home. The 670 has closed transfers, while the 268 has open ones; further, these saws are based on the same crankshaft in the same cases, and have the same bore, for the same displacement. It is my feeling that the finger ported 268 will show less overall port area than the 670; the 670 has two ports, each opening into one wide window, while the 268 splits each side with a divider between them. Husky advertized the 268 as having a little less power than the 670.
I won't have time to measure them tonight, but I promise to get back here when I can with what I find...knowing full well that I will be comparing one specific set of cylinders and not proving or disproving a generality.
The 670 failed when I overheated it on a hot day and stuck the ring. The 268 suffered a similar failure. Interestingly, both saws have run a long time, and both feel as if the crank and rod bearings are near failure...there could well have been a seal reaching the end of it's service life as well.
My point is that both saws gave comparable service for many years and were probably worn out at about the same amount of service life, and that I reserve the right to doubt if finger-ported cylinders are inherently short-lived. I will accept that open ports must be much cheaper to manufacture.
I don't really know if you're right or wrong, but I do happen to have a Jonsered 670 jug and one from a Husky 268 on the bench at home. The 670 has closed transfers, while the 268 has open ones; further, these saws are based on the same crankshaft in the same cases, and have the same bore, for the same displacement. It is my feeling that the finger ported 268 will show less overall port area than the 670; the 670 has two ports, each opening into one wide window, while the 268 splits each side with a divider between them. Husky advertized the 268 as having a little less power than the 670.
I won't have time to measure them tonight, but I promise to get back here when I can with what I find...knowing full well that I will be comparing one specific set of cylinders and not proving or disproving a generality.
The 670 failed when I overheated it on a hot day and stuck the ring. The 268 suffered a similar failure. Interestingly, both saws have run a long time, and both feel as if the crank and rod bearings are near failure...there could well have been a seal reaching the end of it's service life as well.
My point is that both saws gave comparable service for many years and were probably worn out at about the same amount of service life, and that I reserve the right to doubt if finger-ported cylinders are inherently short-lived. I will accept that open ports must be much cheaper to manufacture.
Let me rephrase what I said. Assuming two cylinders have the same port volume and timeing a open port cylinder will wear faster than the same cylinder with closed ports.
Eyeolf, The differance you noticed has to do with the open port model haveing less port area than the closed port cylinder and thats why your comparision is not valid. Thats also why the closed port model has more power.
Eyeolf, The differance you noticed has to do with the open port model haveing less port area than the closed port cylinder and thats why your comparision is not valid. Thats also why the closed port model has more power.
I agree. Open port models are not inherantly short lived. Closed port models will last a slight bit longer though.
Tony Snyder
Addicted to ArboristSite
Enter the 2159 Jonsered; new ball game on the cost of closed ported cylinders.
Will we see this spread across the Big E models over a period of time?
Will we see this spread across the Big E models over a period of time?
eyolf
Addicted to ArboristSite
Jonsered 670 actually has a tiny bit less overall port area than 268, and a teeny bit less port opening...the peak or point of the 268's transfers towards the ex side are a bit higher than the top surface of the rectangular 670 port.
The 268 would seem to actually support the ring more fully than the 670, as the 670's transfers are approx 25mm (across the chord) while the 268's are more like 13mm (each). It seems like the ring would have a harder time expanding into the 4 narrow openings than the 2 wider ones.
268 port width is comparable, overall, to 670, but is split in two sections by divider. Area at full opening, (BDC) may be just slightly greater, but only by a small amount, and port cross section at greatest restriction is less with 268. The 670's greatest restriction is the port opening itself.
It may interesting to note that both depend on cutaway piston skirts on the sides to allow mixture to enter the transfer. Removing cyinder wall material right down to the case would seem to help either one a little, and the 268 could really use a bit more volume high in the tranfer port. Some power gains could be had without messing with port timing and the power-band changes that comes with that.
The 268 would seem to actually support the ring more fully than the 670, as the 670's transfers are approx 25mm (across the chord) while the 268's are more like 13mm (each). It seems like the ring would have a harder time expanding into the 4 narrow openings than the 2 wider ones.
268 port width is comparable, overall, to 670, but is split in two sections by divider. Area at full opening, (BDC) may be just slightly greater, but only by a small amount, and port cross section at greatest restriction is less with 268. The 670's greatest restriction is the port opening itself.
It may interesting to note that both depend on cutaway piston skirts on the sides to allow mixture to enter the transfer. Removing cyinder wall material right down to the case would seem to help either one a little, and the 268 could really use a bit more volume high in the tranfer port. Some power gains could be had without messing with port timing and the power-band changes that comes with that.
HUSKYMAN
Addicted to ArboristSite
One big port will always outflow two smaller ports due to increased area and less frictional loss. I.e. a 4" pipe will flow more than two 2" pipes. This would help account for the 670's increased power over the 268
Assuming the chordal width is not too wide and the port is chamfered correctly this is not a problem. A exception to this is cylinder reed engines with very large intake ports. Engines such as this have been known to wear faster on the intake side only.
timberwolf
Addicted to ArboristSite
True your absolutly right on the principal, but I am concerned with the pipe analagy, the ports are still the same height but ~half the width. This would be better expressed as one 4 inch will outflow two 2.8 inch pipes.
A 4 inch pipe has a 12.6 inch cross section (pi x r sqr)
12.6 divided by 2 = 6.3 divided by pi and srq rooted gives a 2.83 inch diamiter (esentialy saying two 2.8 inch pipes have equal cross section to 1 4 inch pipe). two 2 inch pipes would only have half the surface area and would flow much less.
then the reason for the single 4 inch outflowing the two 2.8 inch is related to the surface area or circumferance of the openings.
4inch x pi = a 12.57 inch circumferance
2.83 x pi x 2 = 17.78 inches of total circumferance
a relationship of 1 : 1.41. Simply stated two round ports totaling the area of a single round port will have 1.41 times more surface area to creat potential resistance to laminar flow. From here you can apply a bunch of rather complicated formulas to get an idea of how much resistance to flow is created, but many factors come into play; gas velosity, temprature, viscosity of exaust gas, density of exaust gas, preasure diferentials, port shape - angel - surface.......
Square or rectangular ports are another story, the greater the height to width ratio the greater the surface area impact of haveing two small ports vs one large. For a true square it is 1 : 1.5.
This also may all be a mute point if the bottle neck is in another part of the system like a small muffler opening.
Not ment to stir the pot, just my 2 bits
Timberwolf
The big pipe outlflowing a couple of smaller ones is a moot point when discussing two strokes as the size of the bore dictates how big the "pipe" can be. Also keep in mind whe are talking about unsteady gas flow not liquid flow. There are some differances.
Gypo Logger
Timber Baron
Can anyone suggest how many thou. I should shave off the base of my 026 pro cyl? Just wanted to make the mods one at a time. My friend has all the shop tools as he makes aircraft parts. The 026 is rated now at 26 hp. after I opened the muffler.
Thanks in advance.
Thanks in advance.
Saw Man
ArboristSite Operative
Two areas often overlooked in the open port vs closed port debate are: 1. The effect on the fuel charge, as the piston skirt becomes a 'port wall ', and 2. The type of piston that can be used.
Both of these greatly affect performance, and component life.
Relative to increased port flow volume is the negative effect of a 'stacked charge'. This is very common in transfer ports that are too large. ie a 4' port vs two 2" ports.
(I'm just using the pipe sizes as examples).
At certain RPM loads the over size port will not deliver all it's flow charge due to port timing. The remainder stays in the transfer port as it is in effect cut off.
This cut off charge is now at a different tempature then that of the fresh intake charge being swept-evacuated from the crankcase up thru the same tranfers port.
Thus flow speed is not optimized, in addition flame propaigation is now affected negatively.
Emissions levels rise, which is a sure sign of less efficient combustion. In effect the maximum potential of cylinder short circuiting is short circuited.
As greater fuel efficiency, and more complete combustion (power) of all fuel charges is attempted, major considerations of: 1. multiple ports which reqiures reduced port sizes, and even more importantly is the placement of port angles to maximize distribution of a clean fuel intake charge.
Ever wonder why some ports are asymertical? Or, longer ports or four port cylinders face the rear?
Noticed the different flow & attack angles? Every one of these and many even more considerations must be factored into an applied design application for each cylinder to acheive optimized performance.
Oh, don't forget costs vs selling price.
Both of these greatly affect performance, and component life.
Relative to increased port flow volume is the negative effect of a 'stacked charge'. This is very common in transfer ports that are too large. ie a 4' port vs two 2" ports.
(I'm just using the pipe sizes as examples).
At certain RPM loads the over size port will not deliver all it's flow charge due to port timing. The remainder stays in the transfer port as it is in effect cut off.
This cut off charge is now at a different tempature then that of the fresh intake charge being swept-evacuated from the crankcase up thru the same tranfers port.
Thus flow speed is not optimized, in addition flame propaigation is now affected negatively.
Emissions levels rise, which is a sure sign of less efficient combustion. In effect the maximum potential of cylinder short circuiting is short circuited.
As greater fuel efficiency, and more complete combustion (power) of all fuel charges is attempted, major considerations of: 1. multiple ports which reqiures reduced port sizes, and even more importantly is the placement of port angles to maximize distribution of a clean fuel intake charge.
Ever wonder why some ports are asymertical? Or, longer ports or four port cylinders face the rear?
Noticed the different flow & attack angles? Every one of these and many even more considerations must be factored into an applied design application for each cylinder to acheive optimized performance.
Oh, don't forget costs vs selling price.
