Does anyone have a well ported STIHL 441, or ran one, if you have what did you think of it by gains?
Anyone run a modded MS441?
- Thread starter Meadow Beaver
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Just wondering because some people say they like the 441, and some people are just religiously against strato saws. Hasn't Brad tried modding a 441?
fredmc
Addicted to ArboristSite
I think it is just fear of the unknown... I've been studying the strato design and I can't see where modding could hurt the motor. I had a 455 rancher that was muffler modded and it had some noticable gains. Increasing flow and increasing compression has to help. The strato design isn't rocket science, it's just more efficient at fuel comsumption and exhaust scavenging
STEVEGODSEYJR
ArboristSite Guru
I have a muffler modded 441 and I think it made a decent gain. Their are several members on here that have a hopped up 441. I think Slamm and Peacock are the two that I can think of right now.
whitemountain
ArboristSite Operative
Thinking of going the 441 route. Could someone chime in on mufffler mods. Specifically pictures and how you did it. I like the idea of a super smooth, gas-sipping power house if such a thing exists. I know more power equals more fuel consumption, but it seems there could be a compromise here somewhere.
Terry Syd
Addicted to ArboristSite
Porting a strato
Over the years I have modded every engine (motorcycle, car, lawnmower) I've ever owned. Now I own a Husky 450 and I can't stop myself from tearing it apart and getting more power from it - it's an addiction, I know...
Here's my take on the strato design as it comes from the factory. It is designed to make good power within a specifed limit of exhaust emissions. If that is true, then it will likely be the exhaust port that holds the key to more power.
As I look into the exhaust port on the 450 I see that the transfers are strongly biased towards the back of the cylinder. I also note that the bottom of the exhaust port sits higher than the top of the piston at BDC. Further, the shape of the exhaust port is a trapisoid (sp?) shape where the top of the port is wider than the bottom of the port.
Without the benefit of an area/timing analysis of the ports, I'm going to state my first impressions of how a strato might be ported to raise the torque peak a bit higher in the RPM range without unduely affecting the fuel consumption.
I would retain the bottom of the exhaust port the way it was designed. I expect that the bottom of the exhaust port standing higher than the piston is to help keep the flow of exhaust gases out the exhaust port from affecting the transfer flows across the top of the piston. Essentially, the higher exhaust port creates an area of relatively low exhaust flow across the top of the piston that allows the transfers to do their job more effectively.
I would not widen the bottom of the exhaust port, even though the top of the port is already wider than the bottom. I expect that the reason the bottom is smaller is again to prevent the flow of exhaust gases from affecting the transfer flow. If the bottom was made as wide as the top of the port it may cause some of the transfer flow to be pulled out the exhaust port.
The port modification that may work is putting an 'eyebrow' at the top of the exhaust port to widen the port out to 65-70% of the bore diameter. The eyebrow should not extend down below the level of the transfer port opening - again, so as not to affect the transfer flow.
This mod would allow a faster blowdown of the cylinder and yet retain the factory designed loop scavenging. The results should be (note how I qualify my remarks) a slight rise in the RPM where max torque occurs.
Any thoughts?
Over the years I have modded every engine (motorcycle, car, lawnmower) I've ever owned. Now I own a Husky 450 and I can't stop myself from tearing it apart and getting more power from it - it's an addiction, I know...
Here's my take on the strato design as it comes from the factory. It is designed to make good power within a specifed limit of exhaust emissions. If that is true, then it will likely be the exhaust port that holds the key to more power.
As I look into the exhaust port on the 450 I see that the transfers are strongly biased towards the back of the cylinder. I also note that the bottom of the exhaust port sits higher than the top of the piston at BDC. Further, the shape of the exhaust port is a trapisoid (sp?) shape where the top of the port is wider than the bottom of the port.
Without the benefit of an area/timing analysis of the ports, I'm going to state my first impressions of how a strato might be ported to raise the torque peak a bit higher in the RPM range without unduely affecting the fuel consumption.
I would retain the bottom of the exhaust port the way it was designed. I expect that the bottom of the exhaust port standing higher than the piston is to help keep the flow of exhaust gases out the exhaust port from affecting the transfer flows across the top of the piston. Essentially, the higher exhaust port creates an area of relatively low exhaust flow across the top of the piston that allows the transfers to do their job more effectively.
I would not widen the bottom of the exhaust port, even though the top of the port is already wider than the bottom. I expect that the reason the bottom is smaller is again to prevent the flow of exhaust gases from affecting the transfer flow. If the bottom was made as wide as the top of the port it may cause some of the transfer flow to be pulled out the exhaust port.
The port modification that may work is putting an 'eyebrow' at the top of the exhaust port to widen the port out to 65-70% of the bore diameter. The eyebrow should not extend down below the level of the transfer port opening - again, so as not to affect the transfer flow.
This mod would allow a faster blowdown of the cylinder and yet retain the factory designed loop scavenging. The results should be (note how I qualify my remarks) a slight rise in the RPM where max torque occurs.
Any thoughts?
Terry Syd
Addicted to ArboristSite
Pulled the jug
Well, I wish I new how to edit the previous post. Disregard everything I wrote. I finally got the time to pull the jug on this saw and look at the mysterious 'Strato' porting.
Although the transfer ports come in from the front of the engine, they come nowhere near the exhaust port opening. In fact, they are located and strongly biased towards the rear. The piston crown carbon indicated the transfer flow stayed entirely on the rear half of the piston.
This thing can be ported like a conventional two-stroke, and I am going to open up the exhaust port just like I was porting a conventional two-stroke. The present exhaust port appears to be about 50% of the bore at the top and tapering to less width at the bottom. There is a small bit of carbon on the piston crown adjacent to the exhaust port that indicates some shrouding by the higher exhaust port floor. I'll take take the floor down to just below the crown at BDC. There is sufficient skirt length.
The intake port is already maximum width. The Strato piston doesn't have much skirt width on the intake side and the port uses every bit of it.
One very obvious defect was the opening to the transfers. The windows in the cast cylinder were much smaller than the transfer ports themselves. A little work with a small square file soon opened them up to the size of the transfer port. I will also drill a couple of holes in the webbing of the cylinder to allow a more direct access of the mixture instead of all of it having to make the turn at the bottom via the lower crankcase half. I could shorten the webbing, however the cylinder bolt holes on either end of the webbing probably create some stress when tightened down. I'll keep the strong webbing, but vent it.
I'm glad I pulled the engine down. The upper 'carburetor' that sends air to the top of the transfer ports was leaking. The whole port was coated with sawdust - not dust, but wood fibers. Thankfully I hadn't used the saw in dusty conditions.
Well, I wish I new how to edit the previous post. Disregard everything I wrote. I finally got the time to pull the jug on this saw and look at the mysterious 'Strato' porting.
Although the transfer ports come in from the front of the engine, they come nowhere near the exhaust port opening. In fact, they are located and strongly biased towards the rear. The piston crown carbon indicated the transfer flow stayed entirely on the rear half of the piston.
This thing can be ported like a conventional two-stroke, and I am going to open up the exhaust port just like I was porting a conventional two-stroke. The present exhaust port appears to be about 50% of the bore at the top and tapering to less width at the bottom. There is a small bit of carbon on the piston crown adjacent to the exhaust port that indicates some shrouding by the higher exhaust port floor. I'll take take the floor down to just below the crown at BDC. There is sufficient skirt length.
The intake port is already maximum width. The Strato piston doesn't have much skirt width on the intake side and the port uses every bit of it.
One very obvious defect was the opening to the transfers. The windows in the cast cylinder were much smaller than the transfer ports themselves. A little work with a small square file soon opened them up to the size of the transfer port. I will also drill a couple of holes in the webbing of the cylinder to allow a more direct access of the mixture instead of all of it having to make the turn at the bottom via the lower crankcase half. I could shorten the webbing, however the cylinder bolt holes on either end of the webbing probably create some stress when tightened down. I'll keep the strong webbing, but vent it.
I'm glad I pulled the engine down. The upper 'carburetor' that sends air to the top of the transfer ports was leaking. The whole port was coated with sawdust - not dust, but wood fibers. Thankfully I hadn't used the saw in dusty conditions.
AUSSIE1
Al.
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Terry, you say you will lower the exhaust and I can see your reasoning, but what timing no's do you think you will end up with?
What percentage of inlet to bore size on that saw?
Don't have any pic's on this webbing your talking about?
Keep us posted on it's progress.
What percentage of inlet to bore size on that saw?
Don't have any pic's on this webbing your talking about?
Keep us posted on it's progress.
Terry Syd
Addicted to ArboristSite
Husky 445/450
Aussie, thanks again for the heads-up in the private email. As for my mods, they will apply for any strato. I am putting my posts in a thread that Rick started on his 445. The 445 is the 46cc brother of this 50cc 450. Here's a link to that thread - http://www.arboristsite.com/showthread.php?t=107976
As I explained in that thread, I have recently moved and I still can't find the cable for my camera. When I finally locate the cable, I'll post pictures of my mods in Rick's thread.
One of the bits of information I would like to obtain is the average compression pressures of the new stratos versus the average compression pressures of the conventional two-stroke motors. It may be the case that with less fuel flushing through the engine the factory may have dropped the compression on the stratos.
Rick and I are discussing that issue and how a larger carburetor will tend to override the strato function. It may be that a larger carburetor will help cool the engine by increasing the fuel flushing through it.
Dropping the floor of the exhaust port was also done to allow a greater area of flow near the bottom of the port. However, it is the top of the port that will flow the most when the pressure is highest. I think I have another mod for the piston that will significantly increase the blow-down of the cylinder prior to the transfers opening - and that's without changing the timing. I would have done the mod tonight, but the recent high winds have dropped a tree in my backyard and I have to use the saw to cut it up tomorrow.
I'll post all my strato mods in Rick's thread.
Aussie, thanks again for the heads-up in the private email. As for my mods, they will apply for any strato. I am putting my posts in a thread that Rick started on his 445. The 445 is the 46cc brother of this 50cc 450. Here's a link to that thread - http://www.arboristsite.com/showthread.php?t=107976
As I explained in that thread, I have recently moved and I still can't find the cable for my camera. When I finally locate the cable, I'll post pictures of my mods in Rick's thread.
One of the bits of information I would like to obtain is the average compression pressures of the new stratos versus the average compression pressures of the conventional two-stroke motors. It may be the case that with less fuel flushing through the engine the factory may have dropped the compression on the stratos.
Rick and I are discussing that issue and how a larger carburetor will tend to override the strato function. It may be that a larger carburetor will help cool the engine by increasing the fuel flushing through it.
Dropping the floor of the exhaust port was also done to allow a greater area of flow near the bottom of the port. However, it is the top of the port that will flow the most when the pressure is highest. I think I have another mod for the piston that will significantly increase the blow-down of the cylinder prior to the transfers opening - and that's without changing the timing. I would have done the mod tonight, but the recent high winds have dropped a tree in my backyard and I have to use the saw to cut it up tomorrow.
I'll post all my strato mods in Rick's thread.
Wild Knight
ArboristSite Guru
Will you post the pics of the 441 you tore down? Give us an update too!
Slamm
Addicted to ArboristSite
I have a ported 441 for over a year now and I wouldn't drop normal size (under 36") with anything else. It is very quick and gets great mileage, I'm probably going to get another one to setup for bucking up.
I drop trees with a 28" bar and would like to buck them up with another 441 with a 24" bar on it. I like it so much I don't use any of my 3 ported 660's much.
My experience with one,
Sam
I drop trees with a 28" bar and would like to buck them up with another 441 with a 24" bar on it. I like it so much I don't use any of my 3 ported 660's much.
My experience with one,
Sam
Wild Knight
ArboristSite Guru
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