Sthil 044 transfer height

[NPKenny]

I've got a 12mm, non-decomp 044 Jug I am working on. The saw is being constructed from multiple boxes of parts and has never been put together. The bottom end is from an MS440.

I'm struggling with the transfers a bit.


Here are the current port opening numbers:

Squish is .019-.021" using a .019" gasket
Exhaust = 100.5
Intake = 71.5
Transfers = 115

Blowdown = 14.5* seems entirely too low.

Any suggestions on finished port numbers given my starting point? I think this jug is an ideal candidate for a cut squish band, but I haven't entered into that realm yet.

Thanks.

 

[wigglesworth]

I've got a 12mm, non-decomp 044 Jug I am working on. The saw is being constructed from multiple boxes of parts and has never been put together. The bottom end is from an MS440.

I'm struggling with the transfers a bit.


Here are the current port opening numbers:

Squish is .019-.021" using a .019" gasket
Exhaust = 100.5
Intake = 71.5
Transfers = 115

Blowdown = 14.5* seems entirely too low.

Any suggestions on finished port numbers given my starting point? I think this jug is an ideal candidate for a cut squish band, but I haven't entered into that realm yet.

Thanks.

The early stihl 044/046 saws, the transfer height was much higher than the latter ones. And, they will run circles around the late model cylinders.

If you look at it, the transfers are angles at the top, not straight across, so in reality, even though the trans peak at 115 there not fully open across the top till around 120.

Are the top fins angled or straight across the jug?

My thoughts, leave the exhaust height, Just widen, clean up the casting in the transfers, and go with 75'ish, maybe more on the intake, depending on how much fuel u want it to use. They run good at 80, just suck a lot more fuel.

Where is the compression? The closer u can get it to 200, the better on a work saw.

Just my opinion... J

 

[blsnelling]

Yes siree. That's actually what you want. 14°-16° is ideal. That's the biggest key to making a 440\460 run.

 

[NPKenny]

That's great news. Thanks for your replies.

It is a straight finned 044 cylinder. I do have an angled fin cylinder and piston, but I decided I would work on the straight finned jug since my bottom end is a 12mm unit.

I don't have a compression reading yet. Last night was the first time I even set the cylinder on the chassis. Squish is right at .020" with a gasket. This cylinder looks to have a wide and flat squish ring with a small combustion chamber so I am hoping for good things.

 

[NPKenny]

Final numbers:

Squish .020
Intake = 75*
Exhaust = 100*
Transfers = 114"

The changes in transfer and exhaust timing came from beveling the port openings.

I have necessary parts like circlips, needle cages, fuel and impulse lines, and an elastostart handle coming on the slow boat from the local dealer. It drives me nuts when I want to work on a saw and the dealers doesn't have one single part for it in stock... Not even the universal ones like starter handles and flippy caps.

 

[Tzed250]

My '94 044 is a 12mm and has the angled fin cylinder.

 

[NPKenny]

My '94 044 is a 12mm and has the angled fin cylinder.

How inter-changeable are the cylinders? The piston that matches my angled fun cylinder is define rely 10mm. I think this straight finned jug I am working with here is probably just after the angled fin model since there is no decomp.

 

[GBD]

I've got a 12mm, non-decomp 044 Jug I am working on. The saw is being constructed from multiple boxes of parts and has never been put together. The bottom end is from an MS440.

I'm struggling with the transfers a bit.


Here are the current port opening numbers:

Squish is .019-.021" using a .019" gasket
Exhaust = 100.5
Intake = 71.5
Transfers = 115

Blowdown = 14.5* seems entirely too low.

Any suggestions on finished port numbers given my starting point? I think this jug is an ideal candidate for a cut squish band, but I haven't entered into that realm yet.

Thanks.

The laws of physics applies equal regardless of model and make! Your sucpition regarding blowdown is correct. Ideally you should lower the cylinder to reduce transfer duration, but you could just raise the exhaust to 97 without widening it to obtain enaugh blowdown timearea without going overboard with total exhaust timearea.

 

[Mastermind]

The laws of physics applies equal regardless of model and make! Your sucpition regarding blowdown is correct. Ideally you should lower the cylinder to reduce transfer duration, but you could just raise the exhaust to 97 without widening it to obtain enaugh blowdown timearea without going overboard with total exhaust timearea.

I disagree on this engine. the numbers Wiggs gave him will make it a runner. We have went to great lengths to study these engines.

Raising the exhaust would kill the torque.......

 

[blsnelling]

The laws of physics applies equal regardless of model and make! Your sucpition regarding blowdown is correct. Ideally you should lower the cylinder to reduce transfer duration, but you could just raise the exhaust to 97 without widening it to obtain enaugh blowdown timearea without going overboard with total exhaust timearea.

Why would you want less transfer duration on this model?

 

[Mastermind]

Why would you want less transfer duration on this model?

Newbies. :msp_rolleyes:

 

[blsnelling]

Newbies. :msp_rolleyes:

It's called baiting

 

[Mastermind]

It's called baiting

I wasn't talking about you Brad. :msp_tongue:

 

[blsnelling]

I wasn't talking about you Brad. :msp_tongue:

You should know by now that you "can't bend the laws of physics". All saws need 25°-30° of blowdown.

 

[tree monkey]

I disagree on this engine. the numbers Wiggs gave him will make it a runner. We have went to great lengths to study these engines.

Raising the exhaust would kill the torque.......

gbd is right on this one
blowdown should be 19-20

 

[Mastermind]

gbd is right on this one
blowdown should be 19-20

ok.....

 

[GBD]

I disagree on this engine. the numbers Wiggs gave him will make it a runner. We have went to great lengths to study these engines.

Raising the exhaust would kill the torque.......

According to scientific studies done by Queens university of Belfast and others during the last 25 years on two stroke performance, a certain BMEP or torque if you want, on a certain engine speed, needs a certain total exhaust timearea, a certain blowdown timearea, a minimum transfer timearea and a minimum inlet timearea. If blowdown timearea is smaller than needed, BMEP will shrink accordingly at that engine speed. The relationship between ET and BT will however match to a lower BMEP at a higher engine speed, and that is where max torque will end up. If you raise the exhaust port to obtain the needed BT, this will give you a higher BMEP or torque at a lower engine speed. This is why it is so important
to keep the transfers low and wide, which again alow for a low exhaust duration.

 

[tree monkey]

According to scientific studies done by Queens university of Belfast and others during the last 25 years on two stroke performance, a certain BMEP or torque if you want, on a certain engine speed, needs a certain total exhaust timearea, a certain blowdown timearea, a minimum transfer timearea and a minimum inlet timearea. If blowdown timearea is smaller than needed, BMEP will shrink accordingly at that engine speed. The relationship between ET and BT will however match to a lower BMEP at a higher engine speed, and that is where max torque will end up. If you raise the exhaust port to obtain the needed BT, this will give you a higher BMEP or torque at a lower engine speed. This is why it is so important
to keep the transfers low and wide, which again alow for a low exhaust duration.

your talking my language
the results are more power using less fuel, better power curve

these guys don't seem to understand this
intake and exhaust port in the 170's transfers in tthe 125 range don't work for a work saw, those are racing numbers

ex 100.5=159 dur
in 71.5=143 dur
tr 115=130 dur

in 75=150 dur
ex 100=160 dur
tr 114=132 dur

if i did my math right, about all you gained is a loss in case presure, this will affect the scavenging, even worse if you widened the port
your intake is a little to short and your transfer is way too long

i don't know if this helps or not

 

[NPKenny]

This discussion has gotten very interesting to me. I see two polar opposite strategies that are attempting to get the same results. If the name of the game is time areas, it seems that both could work, but which would be better.

I have never raised an exhaust port, primarily under the premise that I would be trading torque for useless rpm. However, in every case the premise was widen the exhaust port as much as possible. The thought presented here by GBD would be that if you don't widen the port, you could raise it slightly and increase the blowdown. This is especially relevant in this case where the transfers are already very high in the stock configuration.

Monkey, did you incorporate this thought in your 390 thread? Obviously this is a much different saw, but I remember you raising the transfers pretty dramatically on that one.

 

[NPKenny]

intake and exhaust port in the 170's transfers in tthe 125 range don't work for a work saw, those are racing numbers

ex 100.5=159 dur
in 71.5=143 dur
tr 115=130 dur

in 75=150 dur
ex 100=160 dur
tr 114=132 dur

if i did my math right, about all you gained is a loss in case presure, this will affect the scavenging, even worse if you widened the port
your intake is a little to short and your transfer is way too long

i don't know if this helps or not

It is getting where it might help my understanding. I have a few questions if you are willing to share a bit...

1. Short of dropping the jug pretty dramatically, how can I shorten up this transfer? It was at 115* stock.
2. What intake length would you be looking at, ideally? This cylinder has plenty of room to work with.
3. I widened the exhaust but did not alter the timing... what other approach should have been considered?
4. What are you looking at that makes the indication of case pressure? Relationship of durations?

Like I said above, this is getting really interesting to me.