Hedgerow
HACK
Time/area
If you go with more area, you can reduce time.
And on the intake, improve overall "trapped" volume, and get better and more efficient "push" through the crank case and up around the transfers.
tree monkeys 2153 deluxe
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If you go with more area, you can reduce time.
And on the intake, improve overall "trapped" volume, and get better and more efficient "push" through the crank case and up around the transfers.
Derf
Addicted to ArboristSite
Ok, so it is a wider port so it doesn't need to be as tall? I think I can wrap my head around that... Regarding trapped volume, you're saying that a smaller port has faster transfer velocity? I thought that was more a factor for transfers than intake. But if that is what you mean, I understand the concept.
We're taking about less than 155 here though IIRC.
True. It seems some saws like shorter intakes than others.
Derf
Addicted to ArboristSite
I'm not sure if those are degrees or durations though.
Really wish Scott will chime in to educate us.
Those are durations. Opening ° are I=72°. X=104°. T=125°
Hedgerow
HACK
From the time an intake closes, to the time it hits BDC, it's pushing the fuel charge up and through the transfers.
Every saw design responds differently to transfer height, but most enjoy a little extra crank case compression.
Especially a good stout work saw.
tree monkey
Addicted to ArboristSite
the area of the port window should not be larger then the area of the boot.
the cylinder was lowered a lot, allowing me to raise the roof of the intake a lot, which gave me too much port area. so I raised the flour to correct port area.
this traps more fuel charge in the case
the cylinder was lowered a lot, allowing me to raise the roof of the intake a lot, which gave me too much port area. so I raised the flour to correct port area.
this traps more fuel charge in the case
drf255
BAD CAD
Question TM,
How do you measure your intake floor target?
It seems difficult to get a line you want without multiple assembly and disassembly. There's no ring you can put in there to measure.
I'm thinking a sharpie on the piston at the correct degree, then a lineup afterwards.
It just seems difficult.
Also, on the saws that you didn't raise the intake roof or floor on, did you notice a big difference vs. the ones you raised?
How do you measure your intake floor target?
It seems difficult to get a line you want without multiple assembly and disassembly. There's no ring you can put in there to measure.
I'm thinking a sharpie on the piston at the correct degree, then a lineup afterwards.
It just seems difficult.
Also, on the saws that you didn't raise the intake roof or floor on, did you notice a big difference vs. the ones you raised?
Hedgerow
HACK
One must measure the #'s, but use the force when trying to get all you can out of a saw..
Or use monkey poo..
That works too..
Or use monkey poo..
That works too..
Derf
Addicted to ArboristSite
I think I get it now. Stock, with gasket, the saw has 146 degrees intake duration. When you toss the gasket, it climbs to 150 intake duration. After cutting the cylinder base the intake duration increases to 158 degrees. To get that number back closer to stock you carved out a lot of the roof of the intake port. This reduced the intake duration back to 144 degrees, but the intake port was very tall. The net effect of filling in the port is shutting down the intake port sooner so that there is a longer period of compression as the piston is traveling downward, and therefore greater base pressure that works in favor of maintaining a faster transfer velocity.
Scott, your final numbers (144 in/152 ex/ 110 xfer/20 blowdown) are very close to stock port timing with a gasket (146 in / 150 ex/ 110 xfer/21 blowdown).
Scott, your final numbers (144 in/152 ex/ 110 xfer/20 blowdown) are very close to stock port timing with a gasket (146 in / 150 ex/ 110 xfer/21 blowdown).
The roof of the intake has nothing to do with port timing, only area.
Derf
Addicted to ArboristSite
Yes, I didn't phrase that right. The cylinder moves down with each iterative step to boost compression (removing gasket, cutting cylinder). That increases intake duration. To reduce the intake duration, he raised the floor so the intake opened later and closed sooner. But, he then had a smaller intake opening which reduced flow. I think Scott said he raised the roof of the intake to increase flow (time area), but he could also have widened the intake, or done both.
Im now wondering why Husqvarna set the exhaust so low (@105 degrees from factory)?
Im now wondering why Husqvarna set the exhaust so low (@105 degrees from factory)?
tree monkey
Addicted to ArboristSite
you got it
I didn't widen the intake so I could do more to the piston to get better flow to the transfers
need to plan it out before ya start
I didn't widen the intake so I could do more to the piston to get better flow to the transfers
need to plan it out before ya start
I've tried closer to 100 on the exhaust of a 346. While out ran ok, it wasn't as good as 105-107. It actually made fewer RPMs, not more. Every model is unique.
shorthunter
ArboristSite Guru
Had the chance to run this saw the other day.
Scott built one hell of a work saw
Scott built one hell of a work saw
Hedgerow
HACK
This thread was linked from another today so i read through it again. Thanks Scott.
I am mainly wondering how critical the ex opening between the port and the muffler is? This is a critical event, are there any guide numbers regarding how big the muffler opening should be or is it make it as big as possible?
I am mainly wondering how critical the ex opening between the port and the muffler is? This is a critical event, are there any guide numbers regarding how big the muffler opening should be or is it make it as big as possible?
