Help building,tuning a Strato, Husqvarna 445

[Terry Syd]

H58

Cory at Zama has confirmed that the H58 has the same choke rotation direction as the EL28. Looks like I'll be doing some fabricating.

He also commented about some of the metering lever springs - "The metering springs are as follows 0019014 30gm / 0019002 16gm / 0019009 19 gm / 0019012 25 gm / 0019013 35 gm."

All the springs are measured at the factory installation height. What his list tells me is that the springs are all over the place, that is, there is no rule of thumb like with jets like in float carbs where if you want more flow you can go to the next jet on the list.

He didn't list all the springs available. I note that the EL28 has a 0019011 spring and the H58 has a 0019014 spring. I may have to order a big selection of springs to work out my pop-off pressure.

Of course, you can always tweak the pop-off pressure by bending the lever arm a bit. If you bend it up, it will reduce the pre-load on the spring. Bend it down and it increases the pre-load.

If nobody is interested in this stuff I'll quit posting it. It seems like I am talking to myself.

 

[Husq445]

I'm Listening

Not talking to yourself.

I'm listening. Just have not had a lot of time to post.
I have updates on my phone and check all new posts during the day, just takes too long respond on a Blackberry.

This is all useful info, I just have not had a chance to tear into my carb yet.

Keep Posting, it all looks good.
Thanks Terry

Rick

 

[Husq445]

Ran my 445 yesterday at the Midwest GTG and did pretty good, still waiting for the #s to be posted. Like I had said I put a new ring in it and rechecked the compression and its at 180 psi now. Should be ready to look into doing some more carb work now.

Rick

 

[Terry Syd]

Carb

I got the EL28 installed and did some cutting. The saw is holding the RPM higher in the cut. I need to find a baseline to work from to check my work. I have been making changes and then cutting the odd branch and trunk to check it and there have been too many variables. I can say that subjectively I am sure it is cutting faster, however I need to have a more objective testing method. I used a 2' weathered blackbutt log to set the mixture.

There is still a bit more 'jetting' I need to do right off of idle. When the saw gets good and hot there is a bit of a bog when I hit the throttle WOT. I couldn't get it out with the low speed screw, so I think I may have to re-work the throttle plate.

Everything looks stock and all the bells and whistles on this homeowner saw are connected. It starts just as easy as the stocker.

Zama indicated that they used different metering lever springs to ensure good operation no matter the position of the saw. I tried rolling it on its side a few times and holdinging in the position for a backcut. At idle there was a slight change in tone, but cleaned up as soon as I hit the throttle. I may get a few springs and see if I can clean up the running some more.

I compared the stock 11mm carb metering spring to the EL28 spring - they are identical. The wire gauge, pitch and length are all the same. I had to use a 3X eyeglasses in combination with a 5X magnification glass to check them. I was hoping that they were different so that I could make a swap and see the difference.

It appears the metering screw tapers are the same for both carbs. The exterior part of the screws are different, but inside it is identical. Perhaps the H57/58 carb would have some different tapers. The specs do indicate that they have different metering springs.

The mod wasn't hard, but it definitely is not a bolt-on mod. Lots of little things need to done to make it like a factory install. The biggest change is the choke rotation issue. I have used the liquid metal to create stops for the choke plate and I will see how they wear. If they start to wear out, then I will drill and tap a screw through the body to use as a stop for the plate.

I spent some time shaping the inside of the carb near the main jet outlet in order to clear the choke plate. The plate itself needs to be trimmed as well. When the choke was finally swinging through the proper arc, I then went back with the liquid metal and filled in some areas and also created a ridge that the cutaway in the choke plate will follow. This allows the modified choke plate to actually close off the carb when the choke is closed.

I'm now going to look around for a welder to do some work on the piston crown. 180 psi? Hmm, that sounds good. I was thinking of setting the compression around 165 psi for up here in the hills so that if I do some cutting down below the compression would only go up to about 173 psi.

 

[Husq445]

Wow you gotta take some pics, you are logging everything you are doing, but its rather hard to follow without anything visual for us to see it and compare.

That would help a lot.

We r like little kids gotta have pictures.

Thanks Rick

 

[Terry Syd]

Camera cable

I still haven't found the camera cable. Did I mention I hate moving??

Knowing what I do now, I would start with the H58 carb as it is designed for a saw of equivalent displacement. The idle circuit and throttle plate would be spot on for the 445/450. I would also get a handful of metering springs (weaker and stronger) to see what change, if any, it made to the running of the saw.

I still have the compression increase and the intake tuning to complete. The intake tuning with the boost bottle will be the most interesting. I may even trim the back side of the piston skirt to extend the intake duration if the boost bottle works out. If I can tune the intake wave to pack extra mixture into the crankcase, then I can extend the intake duration and use the intake wave to keep the mixture from blowing back - at least that is the theory....

 

[rmh3481]

Great thread!

 

[Terry Syd]

Symetry of flow

When I tore down the engine to port the exhaust I noticed that the flow patterns on the top of the piston were not mirror images of each other. Since the openings to the transfers were limiting the flow into the transfers (which I fixed), I left the transfer port exits alone until I had confirmed that it wasn't the openings that were giving me a difference in flow from one side to the other.

I cleaned up the piston top and put it back together. After running the saw for a while I have taken it apart tonight and found the same dissimilar flow pattern.

After spending some time looking at the ports I finally noticed dissimilar flow patterns on the back of the transfer port inserts - the part that sticks into the port exit and directs the flow.

I positioned the side plates so that they were up against the top and the back of the port - then tried to put the screws into the plate. That's when the light came on. When I tried to tighten the screws down the inserts shifted.

I had to clean up the bolt holes on the inserts so that the bolts would not change the position of the insert. The inserts should sit up against the top of the port and all the way to the back (intake side). If one or both of the plates shift from that position you will get dissimilar flow characteristics in the cylinder.

 

[Terry Syd]

Spark plug

One of the reasons I tore the engine down was to create a modified extended electrode plug. I need to see how the electrodes sit in the head in order to do it.

The reason for the extra extension on the electrodes is to get the spark gap away from the side of the combustion chamber and more into the center. It may also position the gap in a more turbulent area created by the squish band.

I have done this mod in other engines and it can take about a degree of advance off the ignition timing. In other words, if you want to advance the timing this is a much better way to do it. The timing stays stock, but the flame propagation is faster. It won't cause as much heat build up in the engine.

I don't know if it will work on this 450, but I'll give it a try. I should be able to tell the difference between a stock plug and the modified plug when I do some cutting.

To do the mod you remove the plug gasket and substitute a thin copper or soft aluminum washer (I use an old beer can for material). The plug will then sit deeper into the combustion chamber. However, the plug body will also stick into the chamber, so it has to be trimmed back to the surface of the combustion chamber. You only want the electrodes to protrude further into the chamber.

Usually, the intial thread alignment portion of the plug body will be completely removed. This means when you change the plug you must be extra careful not to cross-thread the plug as you put it in. Always replace the plug by hand and get it a few turns into the head before you put a wrench on it.

I will also 'index' the plug to the center line of the cylinder. This means the outside electrode will align with the center line of the cylinder. To do this requires you put the plug into a drill and use a file to remove material from the base of the plug that the gasket sits on. Just trim enough off that the plug aligns when it is torqued down.

 

[Husq445]

When I tore down the engine to port the exhaust I noticed that the flow patterns on the top of the piston were not mirror images of each other. Since the openings to the transfers were limiting the flow into the transfers (which I fixed), I left the transfer port exits alone until I had confirmed that it wasn't the openings that were giving me a difference in flow from one side to the other.

I cleaned up the piston top and put it back together. After running the saw for a while I have taken it apart tonight and found the same dissimilar flow pattern.

After spending some time looking at the ports I finally noticed dissimilar flow patterns on the back of the transfer port inserts - the part that sticks into the port exit and directs the flow.

I positioned the side plates so that they were up against the top and the back of the port - then tried to put the screws into the plate. That's when the light came on. When I tried to tighten the screws down the inserts shifted.

I had to clean up the bolt holes on the inserts so that the bolts would not change the position of the insert. The inserts should sit up against the top of the port and all the way to the back (intake side). If one or both of the plates shift from that position you will get dissimilar flow characteristics in the cylinder.

I noticed the same on my 445. I only noticed it when I was ready to start porting the transfers. Also check for casting flash, there was a lot of this all over the transfers in mine. Make sure and check the lower tunnels also, the flash was thin but blocked one of the tunnels about 30%

Rick

 

[Husq445]

The plug situation, I think in the chainsaw forum they talked about cutting the electrode off and indexing it around and rewelding back in appropriate position. They also talked about shimming like you are talking about. Go check it out I think the thread isn't more than a week old

Rick

 

[Terry Syd]

Port timing

I don't shim the plug, I take a bit off the base of the plug that the gasket sits on. That saves a lot of time trying to come up with the proper sized shim.

On another note - I put a degree wheel on the clutch and checked the timing of the engine. Here it is -

Exhaust port - 150 degrees
Transfer ports - 126 degrees
Intake port - 144 degrees
Strato port - 120 degrees

Initially I thought the strato port opened before the intake port. However, I later noticed the cut above the wrist pin that has a hole venting it to the crankcase. This cut is the timing cut for the strato function. It keeps the transfer port at crankcase pressure while the strato port is getting in position. When it moves above the transfer port the strato port can then start feeding fresh air to the transfer port.

There is a lot of vacumn behind that strato butterfly when the engine is idling and a lot of gunk gets sucked past the butterfly shaft. I think I may put in some cotton thread packing to stop dust from getting into the engine.

I can see why the engine responds so well to the wider exhaust port and a muffler mod, that exhaust timing is short.

 

[Husq445]

Where did you get the degree wheel, I want to check the port timing on a 350 I am working on?

Just wondering when modders out there start changing the port timing, is there a relationship or ratio that you adhere to or where do you start?


Rick

 

[Terry Syd]

Degree wheel

Just Google - degree wheel - and up will pop various degree wheels. I used one for the old Corvair that came up. I reduced the size to 70% and printed it. The 70% size fit on the clutch. I simply put a drop of contact cement on the paper and stuck it to the clutch. I tied some tie wire to the handle and set the end of the wire at TDC on the degree wheel.

As far as porting specs, you might want to do a search of Timberwolf's threads to get some ideas. The books on porting deal with racing bikes, expansion chambers and generally square bore/stroke motors. Chainsaws are a whole different kettle of fish with the box muffler.

The 450 would probably run stronger if the exhaust duration was about 160 degrees (from what I've read on this site). I noticed when I got the saw and took off the muffler that the transfers were very high compared to the exhaust opening. Now that I've done the math, I still find it hard to believe this thing only has 12 degrees of blowdown.

The piston mod I did with the two scallops in the crown to promote faster blowdown seem less like an option and more like a 'must do'.

If this wasn't a clamshell design I would be dropping the jug and then lifting the exhaust back up a bit. Of course, that would extend the strato timing a bit more, but I'm starting to come around to the idea that the strato timing can help compensate at higher RPM for shorter intake timing.

It will be interesting to see how these statos get modded in the future. A dual carburetor set-up looks like the way to go with a race saw. Set the stato port carb extra rich and then let the extra rich mixture blow out the raised exhaust port. That would promote extra cooling for a race engine.

 

[Husq445]

Cool thanks, found um. Gonna look for some of those threads now.

Rick

 

[Terry Syd]

Intake tuning

Thought I might give an update of where I am at. The extended-extended electrode NGK plug works. The result was a slight increase in torque. I put the 18” bar on and had it buried in some dry Aussie hardwood. I could lean on the saw using more pressure in the cut with the modified plug. I’m going to continue to use the modified plug, although I am monitoring the outer electrode as it does appear to be getting rather hot.

The next phase of testing was to try and incorporate the intake resonance tuning using a ‘boost bottle. Perhaps I should give some background on this idea.

Many vehicles are now produced with their own intake (and exhaust) tuning. It is quite common to see airboxes that have been tuned, sometimes with multiple inlets of different lengths that open at different RPM.. In the early ‘80s it was a common mod to install a ‘boost bottle’ on the intakes. This was usually done to remove a flat spot in the power curve. The concept of boost bottles and tuned airboxes is related to the physics of a Helmholtz resonator. When done right they can give a 10-15% increase in power.

The Helmholtz resonator will resonate at a lower frequency than a straight pipe. This allows a smaller device to be installed when you are trying to create a torque increase at lower RPM. The final tuning of the bottle is by extending or shortening the hose to the bottle. There are different nodes and anodes in the pipe. The primary wave is the strongest, but you tune for whatever works.

I tried various designs of boost bottles on an enduro bike I had. The computations involve calculus and differential equations (or maybe partial differential equations). I decided to try a straight closed pipe resonator. Instead of the hose going to a boost bottle, I just used a very long hose – it ended up over a meter in length. The computations for a closed tube resonator are a lot simpler than the Helmholtz resonator. In fact, I made it real simple. I ran the tube down the side of my bike and just kept moving a pair of needle nose vice-grips to different positions. When I got the effect I wanted, I cut the hose, plugged it, and then repositioned the hose along the frame inside the rear fender. – Intake tuning for dummies.

Now we come to the saw engine. We don’t want low-end torque, we want the extra torque to come in somewhere around 9000-12000 RPM. The closed pipe can thus be made much shorter to work with the higher RPM – short enough that it probably could be slipped up inside the handle for the saw.

After doing the plug testing, I decided to pull the saw apart to attempt the intake tuning. I had filled a small area on the jug next to the intake with liquid weld material. The area was a bit too small for the size of the hose I wanted to use, but I was willing to give it a try and see if I could tune the intake.

There were several problems with the mod, none the least the fact that the saw was a strato. The extra intake opening would create its own wave. Further, I discovered that the strato port had a longer duration than the intake. I would be trying to pack mixture back into a crankcase that was open to the atmosphere via the strato port.

It was after the torque testing with the modified plug that my big ‘ah-ha’ moment occurred. On previous testing the strato port had remained dry, after all, it only feeds clean air to the engine, however this time the strato port was wet with fuel. After spending a good deal of time really lugging the engine down testing the torque I could see I was getting blowback out the longer duration of the strato port.

Well then, this simplifies everything. I will just tune the strato port and make it pack that mixture back into the engine. With the dry air of the strato port I won’t even have to worry about pooling of mixture in the hose. The intake port will be closed when the wave packs the strato port. This looks do-able.

Except I can’t. Although the intake port had an area that I could modify and install a small hose (admittedly it was a bit iffy), there is no way I can figure a way to hook up a hose to the strato function.

I am writing this up in case someone else has a saw they want to give it a go on. A conventional two-stroke would be a candidate, or a strato where there is room for the modification on the longer duration strato port. If someone gives a go, they don’t need to calculate the hose length, just keep clamping it in different spots to see if you find a ‘sweet spot’ that bumps up the torque.

 

[Terry Syd]

Strato timing

The saw is now holding a higher RPM in the cut compared to stock, but what I really want is some more torque for when I have this small saw buried in some wood. That said, it already has more torque than a stocker, but I'll see if I can improve it some more. Since the strato ports are allowing some blowback when the revs drop I am going to decrease the strato timing a small amount.

I've taken a look at the jug and I think I have figured out a way to do it. I'll have to fill in a small amount on the bottoms of the transfer openings. I don't want the liquid weld to come off and be ingested into the engine, so I will be cutting a small trench on the bottom of the transfer opening to give the material a more secure contact surface.

 

[Terry Syd]

Strato timing

I went back and measured the strato port timing - it is 154 degrees. The intake is 144 degrees.

Now here is something interesting about the casting on my jug. The area at the transfer port has been cast a bit lower than the transfer tunnel up to the port. It looks like Husky originally designed the strato port to be timed with the intake.

That is corroborated by the location of the piston at BDC. The piston stands a little bit higher than the bottom of the transfer port - directly in line with the tunnel casting. The height distance is only about 1 millimeter.

And again, there is further corroboration with the casting of the transfer tunnel covers. There is about 1 millimeter of space under the port insert.

It looks like they set the engine up with the ports even to the bottom of the tunnel and then maybe had trouble with emission testing, so they dropped the bottom of the transfer port to get some more air into the engine. Why they didn't just cast a different piston with a higher strato cutaway I don't know. Perhaps some engineer during testing took a flat file to the bottom of the transfer, it worked to pass EPA, and then they went into production with the tweaked jug.

I'll take the bottom of the transfer port up to the level of the piston. That will likely bring the strato timing back to 144 - just like the intake.

Hmm, maybe the boost bottle is back on the table.

 

[Terry Syd]

Front cuttaway

I think I know what the cutaways on the front of the piston are for. As I mentioned above they have holes in them up at the front of the piston - close to the exhaust port.

The temperature gradiants across the piston are likely to be rather significant. With the strato port open the air comes in and flows directly across the piston skirt. Instead of the piston skirt having to conduct its heat out through the cylinder wall to the the outside air - it is getting hit directly on the skirt. However, the front of the piston (at the hot exhaust port) isn't getting that blast of air.

The cutaways above the strato cutaway are open for a little time during the induction phase. The holes in the front of the cutaway will pull fresh air along the front cutaways and into the hot area at the top of the piston next to the exhaust port.

I expect this was a subsequent modification to the piston to give it a more stable expansion. I haven't seen this type of cutaway in any of the strato literature with exploded views of the system, so it is unlikely to be part of the strato function and more likely for piston cooling.

 

[Terry Syd]

A whole lotta work...

I filled in the bottom of the transfer ports. As I worked thorugh the mod I figured I wasn't going to get a big change, perhaps drop the strato timing to 150 degrees - I ended up getting 152.

That was a lot of hard work, and to only get two degrees reduction (or only 1 degree of closing time) was a whole lotta work for virtually nothing. The only other option would to be to weld up the side of the piston and shorten the window - which ain't gonna happen.

I'll give the saw a test in a few days, but I doubt if I could pick the difference.

I came up with another theroy about this strato that may or may not be right. By having the strato timing longer than the intake timing the initial blow-back into the intake system takes place in the strato port.

Whereas the blow-back on a conventional saw will start to significantly richen the mixture, on the strato the mixture simply goes back into the next gulp of air coming in the strato port. When the strato port starts breathing on the next cycle that mixture is pulled down first into the transfer port before the strato port starts moving straight air.

This may give the strato engine a little bit longer power curve (make it more forgiving under load) before the engine starts falling on its face from back-flow.

I wonder if all the stratos are set up this way?