Stihl MS 441 Mods and Results

[Terry Syd]

Stratos

You may want to check out the strato timing versus the intake timing. If you read the 445 strato thread you will see that the two timing figures were quite different. The strato port on the 450 opened for 154 degrees of duration and the intake was at 144 degrees.

I put a bigger carb on the intake (up from 11mm venturi to a 13.5mm) and increased the intake timing. My final figures were 152 on both the strato and intake ports.

My impressions of the Husky 450 strato was that the longer strato timing had a fair bit of influence on how high the saw revved, however it was the intake charge that increased the torque at those revs. I increased the bias of the intake flow (carb and timing) to that of the strato flow and picked up a nice increase in torque at the higher revs.

There is a considerable amount of mixing of the two charges, even though the advertising suggests otherwise. Some of the strato charge is likely to be purged out the exhaust port as the literature states, however the remaining strato charge in the cylinder appears to get mixed in with the intake charge during the squish phase (turbulence) of the compression stroke. A plug check can give you an idea about how the combined mixture is running.

With both strato and intake ports opened, the engine can take big gulps of air. I am already at the edge of my limited coil and won't be extending the intake timing out any further. However, Bitzercreek went to the outer limits on his intake timing and did pick up some nice power up in the revs (he has an unlimited coil on his 455). If a person is running a smaller carb, the increase of intake timing to more than the strato timing could be warranted. I have a larger carb and I can move more air in a shorter period of time - that works for me as I wanted to keep the low end torque of the engine.

I expect that a lot of your power increase came from the increased compression ratio. My clamshell design prevents 'dropping the jug', but I may have a small dome welded on the piston crown in the future. If I can't increase the revs any further, then I might as well increase the torque at the revs I have.

 

[parrishturf]

My final figures were 152 on both the strato and intake ports.

How much taller in thousenths is the port now?

Were you able to point the transfer towards the intake?

Which way should the strato port favor; up, intake, or exaust?

 

[Terry Syd]

Cutting the piston

I'm trying to make all my changes at this point by making changes that aren't permanent. I am changing the intake duration by filing the intake skirt of the piston. The slight change in the strato timing was done by filling the area at the bottom of the transfer port opening with some liquid metal.

If I had an unlimited coil, I would also take a bit off the piston crown at the exhaust port to extend the exhaust duration. Pistons are cheaper than jugs. If I go too far, I can always drop in a new piston and start over.

It is risky to change the factory angles of the transfer ports. The factory has a lot of experience from building many different models of engines. They spend a lot of time testing to get the angles of the exhaust side of the port, the intake side and the roof of the port just the way they want it for the engine. If you have a four-port engine, you will see that both side ports have different angles. Unless you know absolutely that changing the angle will benefit the engine, I suggest you stay with the factory angles.

If you want to try an increase in transfer duration, then cut a bit off the piston crown next to the port. If it doesn't work out, then you can drop in a stock piston and no harm was done.

The modding of the strato engines is in its infancy now. We are trying different things to see what works and what doesn't. Its best to take a slow approach at this time until we establish some principles of modification. It is still a two-stroke, but the strato function does create a new area to explore.

I mentioned the 'biasing' of the intake and strato charge. There is probably a biasing (50/50, 60/40, ?) that will prove to be the best for power without loosing too much fuel economy. I expect that the factory has set up the biasing to favor the EPA regulations. A bit of tweaking could net us some gains and a bigger carb (or a restrictor plate on the strato) may be the answer - we don't know yet.

There is also the variation in the strato and intake timings. I did some testing and found that under heavy load the back-flow of the intake charge would move into the longer duration strato port. That extra intake charge would be utilised on the next cycle of the engine - essentially, as the engine was lugged down the charge biasing would increase. Since a saw engine with a diaphram carb will tend to lean out as the revs drop, the extra fuel from the back-flow recovery of a longer strato port duration will give a flatter fuel delivery. It may be the case that a few extra degrees of closing time on the strato port gives the engine a flatter torque curve. That is, if say 3 degrees extra closing time on the strato gives a flatter curve, then as we increase the intake duration we also increase the strato duration to keep the 3 degrees difference.

It would be nice to have a dyno to test out these ideas to develop some specific principles for modding stratos.

 

[bitzer]

That 441 needs to get into some wood with a stop watch to see what you really did. Best case scenario would have been to make some times stock and then after modding in the same consistant log to see how well you did. The lean number 15+k means nothing. It is the highest rpm the saw four strokes that will be where the gain in rpm is seen. If the saw is not four stroking it is lean. From what I have read and experienced the stratos don't gain much in max rpm. They gain torque. My ported Husky 455 is at around 12.7k max WOT off load, but in the wood it runs with a ported 59cc classic two stroke that runs around 13.5k WOT off load. If the saw is four stoking WOT off load when it is hot it doesn't matter where the H and L screws are as long as it is four stroking. Like Terry said, we are on the cusp of strato modding and there are a lot of pathways to be explored. I wouldn't touch the strato ports on the cylinder at all. If anything you are going to want less air coming in there as Terry found out in the 445 thread. There is a lot of great info in that thread and it is worth the read when dealing with stratos. Also extending the top of the transfers back toward the intake is common with porting these saws. Raising or lowering the transfers increases duration and changes timing. I did raise the top end of my transfers and raised the transfers at the cylinder flange, but the 455 is a clamshell and a very different design from the 441. Get the saw four stroking without a tach on it and make some timed cuts to see where it wants to be. Then put a tach on it. The tach is merely for reference. It doesn't really mean anything when it comes to a modded saw.

 

[Terry Syd]

Degree wheel

Another good idea before removing any metal is to put a degree wheel on the engine and find out what the stock timing figures are. Then as you start cutting it will help you keep perspective on your mods as you're removing metal.

We also need to start assembling a data base of strato timing figures, both stock and modded, so that we will be less in the dark than we are now. If everyone posted their timing figures, then it should become easier to establish some strato porting principles.

 

[bitzer]

Another good idea before removing any metal is to put a degree wheel on the engine and find out what the stock timing figures are. Then as you start cutting it will help you keep perspective on your mods as you're removing metal.

We also need to start assembling a data base of strato timing figures, both stock and modded, so that we will be less in the dark than we are now. If everyone posted their timing figures, then it should become easier to establish some strato porting principles.

Good idea Terry! I've been thinking the same things. We need to establish a baseline for strato modding. I am kicking myself for not degreeing first and documenting better. Hopefully others can follow with a better data example.

 

[parrishturf]

Stage Two Mods 441

How the stock 441 saw cut in wood is for Stihl to worry about...

I realize how a more scientific aproach would help, but grinding on a port is an art. You have to experience the chip removal, and the regret!!!

Today I opened the saw up to stage 2:

Intake to 20mm width.(Limited by piston width)

Exaust to 33mm width.(Limited by Ring locator pin, could go much wider realitive to piston.)

Had some detonation marks at piston edge from prior compression increase, relieved edge about .010.

Removed cylinder skirt laterally and blended into transfer ports.

Opened muffler up with cut between two 3/8 inch holes 1.5" apart.

Blended rubber intake manifold into intake port, removing all diamond moldings in manifold, removed both metal intake gasket rings.

Very little tuning required for any desired top rpm 13500 to 15960 easily adjustable. Both with dark plug.

Fuel is amsoil 1:100 of course...

Its, time to cut wood! :greenchainsaw:

 

[bitzer]

How the stock 441 saw cut in wood is for Stihl to worry about...

I realize how a more scientific aproach would help, but grinding on a port is an art. You have to experience the chip removal, and the regret!!!

Today I opened the saw up to stage 2:

Intake to 20mm width.(Limited by piston width)

Exaust to 33mm width.(Limited by Ring locator pin, could go much wider realitive to piston.)

Had some detonation marks at piston edge from prior compression increase, relieved edge about .010.

Removed cylinder skirt laterally and blended into transfer ports.

Opened muffler up with cut between two 3/8 inch holes 1.5" apart.

Blended rubber intake manifold into intake port, removing all diamond moldings in manifold, removed both metal intake gasket rings.

Very little tuning required for any desired top rpm 13500 to 15960 easily adjustable. Both with dark plug.

Fuel is amsoil 1:100 of course...

Its, time to cut wood! :greenchainsaw:

How it cut stock is how you measure your progress. Sure grinding is an art, but it also takes port maps, measuring, and planning to avoid the regret. The diamond moldings are there for a reason and I don't know what you mean by removing the metal intake gasket rings. I still have no idea what you are getting at with your 13.5k to 16k rpm figures. I haven't run amsoil, but I wouldn't run anything less than 40:1 in a ported saw no matter how good the oil is supposed to be. Its your saw though. Probably not detonation from compression either. Too lean more likely. 175psi is not that much. I have a saw at 190 and I've heard of over 200 with a pop-up. What rpm is the saw four stroking at WOT off load? Not trying to beat you up here just trying to figure out where you are at. Also the ring ends are on the intake side, not the exhaust side.

 

[parrishturf]

How it cut stock is how you measure your progress. Sure grinding is an art, but it also takes port maps, measuring, and planning to avoid the regret. The diamond moldings are there for a reason and I don't know what you mean by removing the metal intake gasket rings. I still have no idea what you are getting at with your 13.5k to 16k rpm figures. I haven't run amsoil, but I wouldn't't run anything less than 40:1 in a ported saw no matter how good the oil is supposed to be. Its your saw though. Probably not detonation from compression either. Too lean more likely. 175psi is not that much. I have a saw at 190 and I've heard of over 200 with a pop-up. What rpm is the saw four stroking at WOT off load? Not trying to beat you up here just trying to figure out where you are at. Also the ring ends are on the intake side, not the exhaust side.

Bob,

I will try to review, This saw was very high millage and free. My goal was to see what could be done with this unique product if money was out of the equation. Free saw with ok rings and cylinder. No drive assy, clutch, bar, etc...

Stock: the saw works well and is documented else-were. My first work on the saw was to see what fuel, mild port work, and compression increase, could be had and how much effort/benefit. It seams most folks here are not getting what I was offering. A stock 441 will not tack as high as my moded engine, open shaft on both. After doing exactly what other modders would do to any two stroke. Make it breath etc, no welding on the piston, or carb changes. Just working with whats there, this saw came alive, and torque in your hand is OMG!

I have a new 441 and will do a tear-down and post measurements for future. When we can make some timed cuts on both saws, I will post that.

Shortly I will post pictures of the stage 2 port work. The tiny transfers under jug are now open wide.

If you have never had one of these saws apart its hard to imagine the strato ports and transfers. Also the metal ring is behind the carburetor to stiffen the rubber manifold. The diamonds are cast inside the manifold to create turbulence (I realize this) in a stock saw. I have opened the manifold to match my new port size and shape, and added my own swirl shape.

I think the reason muffler mods of old haven't worked is due to the transfer ports. You really would not believe how small they were, and how much linear edge they had, put a big pipe on the muffler fine but nothings coming out of that crankcase.


The point is strato porting is going to replace the standard saws in the stihl lineup at some point. At least the concept of a green saw will. So when the 881 comes along I want to be ready.

 

[bitzer]

How do you know what kind of torque you've got if you haven't cut with it yet? I haven't ported a stihl strato, but I have ported a husky strato. Brad Snelling posted pics of the cylinder of the 362 and he said the 441 design is identical so I haven't held it in my hand, but I know what it looks like. What rpm is the saw four stroking at? I can lean a saw out all day and cause it to make high rpms. I just don't get what you are getting at. You ported a strato based on classic two stroke principles and you got results. So have others and I am one of them included. I didn't do a pop up piston or add metal any where. My Husky is a clamshell so I can't even lower the jug, I just widened the exhaust and intake, raised the transfers and modded the muffler and made a 56cc strato out run a mildly muffler modded 64cc Stihl 390. It seems like we are not on the same page. Brad snelling just posted videos of a 441 he modded recently that he claimed was holding 11.5k in the wood. I asked him if he ported it like a classic two stroke and he said he did. Others like Tree slinger have done the same. I am just wondering what rpm your saw is four stroking at. Also what do you mean by "open shaft?" No B&C?

 

[parrishturf]

How do you know what kind of torque you've got if you haven't cut with it yet? I haven't ported a stihl strato, but I have ported a husky strato. Brad Snelling posted pics of the cylinder of the 362 and he said the 441 design is identical so I haven't held it in my hand, but I know what it looks like. What rpm is the saw four stroking at? I can lean a saw out all day and cause it to make high rpms. I just don't get what you are getting at. You ported a strato based on classic two stroke principles and you got results. So have others and I am one of them included. I didn't do a pop up piston or add metal any where. My Husky is a clamshell so I can't even lower the jug, I just widened the exhaust and intake, raised the transfers and modded the muffler and made a 56cc strato out run a mildly muffler modded 64cc Stihl 390. It seems like we are not on the same page. Brad snelling just posted videos of a 441 he modded recently that he claimed was holding 11.5k in the wood. I asked him if he ported it like a classic two stroke and he said he did. Others like Tree slinger have done the same. I am just wondering what rpm your saw is four stroking at. Also what do you mean by "open shaft?" No B&C?

Bob,

At this point I do not... their is no bar and chain or clutch on this engine. As Mr. Snelling said, the saw ports well and runs rich. I plan to place this jug onto the new saw at some point.

The transfer ports under the 441 are tiny compared to the 362, and the stock base gasket interferes as well as the crank case and cylinder skirt. I made a choice to remove the skirt all along the sides of the ports under the jug, and left the skirt fore and aft of piston skirt. This is something i have done on motorcycles, do not know if others do it on saws.

If you want pictures I will email, directly.

 

[bitzer]

What Terry Syd is trying to do and what I have been attempting to do is find the point at which the strato function can be manipulated for optimum performance of the saw. As others and I have found a classic port job will have good gains in a strato, I believe that there are greater gains to be found in an attempt to manipulate the strato function to its limits. It is trying to find the ratios and what works or does not work that is the challenge right now. Running a saw at WOT with no B&C is not a good idea ever and I would guess that most would agree with me. I still would like to know at what rpm is the saw four stroking? If its not four stroking at those numbers its lean and with no B&C the powerhead will be toast very quickly.

 

[parrishturf]

What Terry Syd is trying to do and what I have been attempting to do is find the point at which the strato function can be manipulated for optimum performance of the saw. As others and I have found a classic port job will have good gains in a strato, I believe that there are greater gains to be found in an attempt to manipulate the strato function to its limits. It is trying to find the ratios and what works or does not work that is the challenge right now. Running a saw at WOT with no B&C is not a good idea ever and I would guess that most would agree with me. I still would like to know at what rpm is the saw four stroking? If its not four stroking at those numbers its lean and with no B&C the powerhead will be toast very quickly.

Bob,

At no point has the saw been run lean. That was my original question, How?

The saw can be set to burble and self limit at any number you want, the highest so far is 15960, with "four stroking" burble.

If you have some specific advice or settings you would like to see tried pass it on.

The strato port casting at the manifold are tiny, I opened them up and blended them back into the rubber manifold. It would be possible to remove the divider from the manifold and knife edge the bridge between both strato ports at the casting instead. The butter fly for the strato could be enlarged and bring in more air. Someone said the side skirts hold a puff of air, I don't think thetas so. Their are pictures on AS that show the flow path. It seams to me that the total intake is almost exactly the sum of both paths. The fact that my saw has stayed rich suggests what you were getting at, the strato ports are an area to focus on.

One limit on the exhaust is the ring locator pin; the end of the ring is shorter than the piston skirt on the exhaust side. Have already had it hook during assembly and had to really champfer the upper port and polish the champfer in. (Can a port be asymetrical?)

By the way, Amsoil 1:100 or 1:80 is unbelievable. It will clean up existing sludge. Stihl oil does leave a gel that looks like black carbon residue that if not removed with the Decarborizor Solution will harden and lock the rings. The pictures of the 441 your friends post shows that residue clearly. The Decarborizer is cheap and works well, but, the Amsoil just works in everything. We run it in 4 strokes too. Try it in an old saw. clean out the crank case with carb cleaner spray put a little amsoil on the rod bearings warm the saw, use it for 20 min, and tear it down the crank case and bearings will be wet and slicker than ever, and the saw will carb better than ever.

 

[bitzer]

Bob,

At no point has the saw been run lean. That was my original question, How?

The saw can be set to burble and self limit at any number you want, the highest so far is 15960, with "four stroking" burble.

If you have some specific advice or settings you would like to see tried pass it on.

The strato port casting at the manifold are tiny, I opened them up and blended them back into the rubber manifold. It would be possible to remove the divider from the manifold and knife edge the bridge between both strato ports at the casting instead. The butter fly for the strato could be enlarged and bring in more air. Someone said the side skirts hold a puff of air, I don't think thetas so. Their are pictures on AS that show the flow path. It seams to me that the total intake is almost exactly the sum of both paths. The fact that my saw has stayed rich suggests what you were getting at, the strato ports are an area to focus on.

One limit on the exhaust is the ring locator pin; the end of the ring is shorter than the piston skirt on the exhaust side. Have already had it hook during assembly and had to really champfer the upper port and polish the champfer in. (Can a port be asymetrical?)

By the way, Amsoil 1:100 or 1:80 is unbelievable. It will clean up existing sludge. Stihl oil does leave a gel that looks like black carbon residue that if not removed with the Decarborizor Solution will harden and lock the rings. The pictures of the 441 your friends post shows that residue clearly. The Decarborizer is cheap and works well, but, the Amsoil just works in everything. We run it in 4 strokes too. Try it in an old saw. clean out the crank case with carb cleaner spray put a little amsoil on the rod bearings warm the saw, use it for 20 min, and tear it down the crank case and bearings will be wet and slicker than ever, and the saw will carb better than ever.

That is what I was getting at. If the saw is four stroking at 16k then you should be fine although that is high for a work saw and the number will change when you put a b&c on it. The ring ends are always on the intake side not the exhaust. You said the saw was free, is it possible that the previous owner put a new piston in it backwards? Here is a video of a strato that Husky sent me when I asked for their concept of the theory. This is actually the same engine I have worked on. I know it is not the same as the Stihl, but it shows the concept well. Stihl gave me very little info when I asked them. I have not tried amsoil and those who have claimed good success.

http://www.youtube.com/watch?v=IY7zQKw4qsQ

 

[parrishturf]

That is what I was getting at. If the saw is four stroking at 16k then you should be fine although that is high for a work saw and the number will change when you put a b&c on it. The ring ends are always on the intake side not the exhaust. You said the saw was free, is it possible that the previous owner put a new piston in it backwards? Here is a video of a strato that Husky sent me when I asked for their concept of the theory. This is actually the same engine I have worked on. I know it is not the same as the Stihl, but it shows the concept well. Stihl gave me very little info when I asked them. I have not tried amsoil and those who have claimed good success.

http://www.youtube.com/watch?v=IY7zQKw4qsQ

The stihl strato port is different. The lower ring end is at eleven oclock on exhaust side, It chunked last night.

I am going to relocate the pins in the future to match the ms 362. Both are at about 7 oclock on intake side.

Pictures will be up tonight. The new 441 and 460 comparison is going on now, tear down and pictures later.

 

[nanuk]

Ring Ends?

The stihl strato port is different. The lower ring end is at eleven oclock on exhaust side, It chunked last night.

I am going to relocate the pins in the future to match the ms 362. Both are at about 7 oclock on intake side.

Pictures will be up tonight. The new 441 and 460 comparison is going on now, tear down and pictures later.

How do you go about changing the ring pins?
can they be driven out, and a hole redrilled and re-installed?

or do you grind them away, and drill new holes and use drill rod to press in?

 

[bitzer]

The stihl strato port is different. The lower ring end is at eleven oclock on exhaust side, It chunked last night.

I am going to relocate the pins in the future to match the ms 362. Both are at about 7 oclock on intake side.

Pictures will be up tonight. The new 441 and 460 comparison is going on now, tear down and pictures later.

What do you mean chunked? Every saw I have ever been in the ring ends are on the intake side.

 

[parrishturf]

441 mod Pictures

The 441 has the lower ring ends are on the exhaust side!!!


View attachment 120039

View attachment 120040

View attachment 120041

View attachment 120042

Here are pics of piston failure, and the small intake.

Without relocating the pin the stock saw can only go about 1mm wider on the ring side.

 

[parrishturf]

Pictures

Here are all the pictures of the modded 441 jug. You will note the ring locator pin in exhaust, after cleaning up the mess the ring made the port is now too wide. About 81% of skirt. I did run the saw with all mods and one ring. The accelleration is great but down on torque in hard wood. Installing the stock muffler brought most of the torque back. I am welding the piston and will move the locator pin. The port timming is next...


http://cid-1eeab322ae16dc89.skydrive.live.com/self.aspx/Public/MS441mods 076.jpg

The videos are of the stock 441 and a stock 460 in hard wet red oak. Their is even a Jonesred tossed in...

http://cid-1eeab322ae16dc89.skydrive.live.com/self.aspx/Public/MS441mods 087.MOV

 

[parrishturf]

How do you go about changing the ring pins?
can they be driven out, and a hole redrilled and re-installed?

or do you grind them away, and drill new holes and use drill rod to press in?

At this point grinding is the only way I can remove them and not foul up the ring land. If you have a 441 and pull the piston you will note a large bulge inside the piston head at both the pin insertion points. The pin appears very long. I am going to try to drill and insert a piece of drill bit and see how tightly I can press it on an old piston. I may have to weld a bulge just like the original pin is in to get enough length of engagement. The 441 piston are 135.00 ea and a jug/piston is just over 300.00. We are about 2K into the 441/460 pair with spares at this time.


I hate to speak poorly of the Gov. but I swear they put that pin their to stop porting!