Help building,tuning a Strato, Husqvarna 445

[Terry Syd]

Another cylinder

A jug doesn't cost all that much to replace if things go wrong. Think of all the ported expensive cylinder heads that have ended up stacked in the back of shops. I do like to keep my expenses down though.

If you did get another cylinder to work on, you could then apply everything you've learned from this exercise. Plus, you could have an old piston to try out various mods before you modify the new cylinder.

You could widen the exhaust without raising it and you could match the strato port and intake port timings. Then, running the old piston in the new cylinder you could try other timings.

If you wanted to try a bit more intake timing you could trim the intake skirt, say 4 degrees. If that worked out, then you might lower the intake in the jug, say 2 degrees - for a total of 6 degrees further duration. If that was too much, then when you put a new stock piston in you will still have 2 degrees of metal to work with. Trim the skirt 2 degrees and be confident you got it right.

The same with the exhaust timing. You said you took the exhaust up about a millimeter on the present jug. You could run the new cylinder with the stock timing and the wider port to check it out. Then try trimming 1/2 millimeter off the exhaust side of the piston to advance the timing. If it was too much, then installing the stock piston would fix it. If the extra exhaust duration worked out, then you could raise the exhaust port window 1/2 millimeter. If that was too much, then when you put a new stock piston in it will have the desired 1/2 millimeter increase over stock.

I've butchered a few old pistons playing around with timing.

 

[bitzer]

I timed my 455 against a Stihl 310 and 390 today. The 310 I ported and opened the muffler. The 390 has a mild muffler mod, but otherwise is stock. The 455 and 310 both wear a 24" bar and the 390 wears an 18" bar. I sharpened the two 24" chains with my electric bench grinder and the 18" chain is new. All the chains are Stihl 33rsc. The wood I made timed cuts in was 10" Basswood and was consistant throughout. I made five cuts with each saw and these are the best times which were made lightly dogging in. I also switched the B&Cs on the two Stihls to see how they compared.

455 w/24"-6.1 secs
310 w/24"-6.4 secs
390 w/24"-6.7 secs

310 w/18"-3.4 secs
390 w/18"-4.4 secs


I did not put a tach on the saws while in the wood. Its tough to hold a stopwatch and watch a tach while making a cut! Ha. Ha. I will tach them in larger wood and time them again to see how they compare a different day. Today I ran out of the log I was using and I have other things to do. Obviously I gave the 310 some speed and maybe a little more torque on my port job, but not much. It will be interesting to see how they all hold in 15 and 20" wood. The 455 seemed to hold its rpms the best out of the 3 with the 24" bar on it. I was able to put more pressure on it before bogging down. I also tached them all after these cuts were made at off load WOT and just at four stroking.

455-12,680
310-13,560
390-13,000


The results are all well and good and if I made a 56cc saw run with a mildly muff modded 64cc saw thats great, but it doesn't amount to much if the damn thing will die after idling for 10+ secs. Obviously none of these saws are pro saws and all are clamshell crank cases with open transfers (other than the 455). Their stock HP numbers are lower than pro saws in the same cc class and they have a wider powerband. If not for the damn pooling I would say I did alright. Oh well, lesson learned and now looking for a new jug to play with.

 

[drkptt]

...
I know transfers were originally at 132 or so. When I raised them I angled them up from the exhaust side to the intake side. So the exhaust side of the transfer is still stock, but on the side closet to the intake it is at 140. What will shortening the blowdown do in terms of power? I know it will get more fresh mix into the chamber faster, but what am I robbing by doing so? I will keep the saw apart for now just in case I do have these wrong.

You've got to consider the cylinder pressure when the transfers open. If there's not enough blowdown the pressure in the cylinder will be higher than the crankcase and exhaust will flow down the transfers at first. This won't help getting fresh charge into the chamber.

If you're going to raise the transfers and not raise the exhaust timing edge then it would be a good idea to increase exhaust blowdown (mass flow) by increasing the exhaust port area, relieving muffler restrictions, or tuning the exhaust (if that's an option).

I don't know about strato transfer timing but a technique used by some manufacturers to improve emissions of standard (homogeneous charged) engines was to purposely raise the transfers so there was backflow. This shot of hot gas helped vaporize any droplets of fuel, but it sure wasn't done to improve power.

 

[Terry Syd]

Congratulations!

Nice work, obviously you didn't hack things up too bad - the bloody thing hauls.

Ok, as a stop-gap measure on the 455. Since it it loading up at idle, you can lean out just the idle mixture, but keep the same mixture strength as the butterfly moves across the transition ports.

The easiest way is to drill a small hole in the throttle valve butterly - I mean the smallest drill you have. If that helps, but you need a bit more air, then you can drill another one next to it to lean it out some more.

This won't affect the tuning on the transition ports or the main jet, it will just lean the idle. If you go too far, then solder or epoxy up one or all the holes.

 

[bitzer]

Thanks for the tip Terry! I may have to do that. The pooling is not as bad as I originally thought tho. I worked with the saw today for 3 hours, limbing and bucking trees I had felled a few weeks ago. For constant work it ran fine, meaning less than 10 seconds at idle after WOT. Between 10 and 15 seconds I can hear the rpms drop, but I can still rev it back up with a pump or two of the throttle. At 20 to 25 secs it takes some feathering on the throttle, but I could usually bring it back. After 30 seconds it was tough to bring back and would die. When I work with this saw I usually don't let it idle for more than 10 seconds so generally it will be fine. This is also not a primary work saw of mine so I may have lucked out to some extent. I also think I may have been a little rich at WOT. Its really hard to tell where this saw wants to be. It will just take some further testing. I found a nice black maple log that I cut green a month or two ago today while digging thru the pile. It must be close to 18" or so. I will do the same tests that I did today on that one and see how it holds up against the others. Thanks again Terry!


I forgot to mention that before any porting was done to any of these saws they all had muffler mods and I timed all of them months ago. The 455 was always at least 1 second behind the other two, while the other two were always neck and neck.

 

[bitzer]

You've got to consider the cylinder pressure when the transfers open. If there's not enough blowdown the pressure in the cylinder will be higher than the crankcase and exhaust will flow down the transfers at first. This won't help getting fresh charge into the chamber.

If you're going to raise the transfers and not raise the exhaust timing edge then it would be a good idea to increase exhaust blowdown (mass flow) by increasing the exhaust port area, relieving muffler restrictions, or tuning the exhaust (if that's an option).

I don't know about strato transfer timing but a technique used by some manufacturers to improve emissions of standard (homogeneous charged) engines was to purposely raise the transfers so there was backflow. This shot of hot gas helped vaporize any droplets of fuel, but it sure wasn't done to improve power.

I did raise the exhaust and widened it to 65% or so of the bore diameter. The muffler is dual ported as well. I think the strato air gives enough pressure to sweep the exhaust out hence the shorter blowdown on these saws to begin with. These stratos are a whole different animal I think from the classic two strokes.

 

[Terry Syd]

Pooling

Bob, the pooling doesn't sound that bad, so maybe just one little hole might do the trick. You will probably have to turn down the idle screw, but that's no biggie.

What is happening in your saw is that the backflow into the carb is picking up extra fuel when it flows back again across the idle circuit (double dipping?). The hole in the butterfly will not only lean out the mixture, but the air backflowing through that hole will not pick up any fuel on it's way back to the engine (no double dip).

There does seem to be a substantial improvement in the saw's power. It looks like you may have inadvertently taken strato biasing to the limits. I wish I didn't have this limited coil problem, I'd like to get a bit more power out of my saw. Right now it is a pain during light cutting with the limiter making the engine hick-up. I find myself pushing into the wood harder to stop the misfiring. During limbing it was so annoying that I increased the fuel flow so I didn't have to listen to the misfire. I gotta get a new coil.

 

[bitzer]

What size drill bit do you think I should use? I will look today for the smallest I can find. Do I need a size like boring out a jet or can I go bigger? I think I would have to do some searching for something of that size. I am going to go to a couple of hardware stores and see what is the smallest available. I am really not confident in filling holes in that are too big. I just think whatever I would use would break free eventually. I agree on the limiter. I was happy to hear about mine and hopefully you can get something to work.


Inadvertantly more power? Come on Terry that was all planned! Ha. Ha. I'm just glad its doing what its doing and not completely destroyed!

 

[drkptt]

I think the strato air gives enough pressure to sweep the exhaust out hence the shorter blowdown on these saws to begin with. These stratos are a whole different animal I think from the classic two strokes.

How could that be? That pressure is still developed in the crankcase and depends on charge density and crankcase compression ratio. If anything the crankcase compression ratio is lower because of the longer transfer port ducts.

 

[Terry Syd]

1 mm

I was thinking of a drill somewhere around the .5mm - .75mm area might be about the right size (could be wrong, been that before). As far as 'falling out', that's why I will use solder. When you heat up the brass throttle plate, the solder will slip into the small hole by capilliary action. It won't come out. That's why it is better to use a series of small holes to find the right amount of air, rather than drilling one big one - you want the solder to be able to fill up the hole.

I use to make a mod at the top of motorcycle throttle slides that would lean out the idle, but make it rich just off idle (it was to eliminate lean detonation when shutting down from speed). The hole in the front of the slide would be a fair size, but the hole at the back of the slide that controlled the air to the engine was calibrated in conjunction with a larger idle jet. If I ever got the idle hole too big, I just filled it in with solder and re-drilled it smaller. I never had a problem with the solder coming loose.

For drills, a model shop will likely have a great selection of very small drills.

 

[bitzer]

Thanks for the info Terry. I went to a couple of hardware stores and the smallest I could find was 1mm. I will keep looking.

Interesting development on timing the three saws again. I used a 24" bar for all three on this test with a brand new out of the box Stihl 33rsc. The wood was 15" Black Maple and was green and very consistant. It would have made great lumber instead of cookies but oh well. I don't know if you are familar with basswood or black maple, but the maple is a much denser harder wood. The basswood is about as soft as decent hardwoods get. Here are the times:

455- best time = 14.78 secs. Averaged 14.78-15.79 Often closer to 15.5
310- best time = 14.54 secs. Averaged 14.54-15.40 Often closer to 14.9
390- best time = 16.78 secs. Averaged 16.78-17.68 Often closer to 17


The 455 was best with consistant moderate pressure, leaning on it really slowed it down. The 310 was also best with consistant moderate pressure, leaning on it slowed it down, but not as much as the 455. The 390 was also best with mod. consitant pressure, leaning on it slowed it down more than the 310, but not as much as the 455. As soon as I was into the log on all three saws I could feel the 310 and 455 running much faster thru it compared to the 390 and with the work I did to them they should. I was amazed at how much they did pull away though. I guess I did alright. I still did not tach them in the wood, but I have some more of that maple around. It was a forest tree, nice and strait for about 50 feet with no knots. The top had blown off and it had to be taken down. I probably won't be back at it until next week some time on testing and drilling. I think I am happy witht the results, but I wish I would have documented and measured better, because there really is no blue print or decent proof of what works. When I have the saw apart again I will measure the strato timing with the transfer covers off. Thanks again Terry!

 

[bitzer]

How could that be? That pressure is still developed in the crankcase and depends on charge density and crankcase compression ratio. If anything the crankcase compression ratio is lower because of the longer transfer port ducts.

You are right "pressure" is the wrong word. I guess I mean that the strato air blows out the exhaust instead of the fresh mix so you don't lose any fuel in the process like a classic two stroke. I think that is why they have a shorter blowdown to begin with, but I could be wrong. You are probably right about the crankcase pressure. I am not really sure though.

 

[Terry Syd]

Size matters

I initally thought about 1mm, then had to shift my thinking to the size of the saw engine. I'm not used to working with 50cc engines. The 1mm drill may work. However if it is a bit too big you could just hit one side of the hole with some solder.

Or, you can try some epoxy to the side of the hole. The epoxy would be easy to experiment with, easy to remove, and if it did come off it wouldn't hurt anything. You would also have a better idea about the size of the hole/s you want.

 

[Terry Syd]

More blowdown

After perfecting my chain sharpening skills some more, I now have the chain self-feeding into the wood. As it pulled down into the wood, it would also pull the revs away from the coil limiter.

I decided that I could try to pick up some more blowdown by increasing the exhaust duration a bit. I nipped a bit off the front of the piston (less than .5mm) and increased the duration from 150 degrees to 154. That extra 2 degrees of blowdown gave me a 17% increase in blowdown during the time of highest cylinder pressure (when the port opens).

The result was impressive, the saw is cutting faster and holding the revs well. I didn't have any problem with the coil limiter, so I am going to take another nip off the piston and extend the duration to 158 degrees.

Taking the extra bit off the piston was easy as I already had the curvature of the port cut into the crown. I just kept trimming the piston in the center of the port and looking at the degree wheel. When I had 154 degrees of duration, I just matched up the rest of the piston. All the work was done with the jug mounted on the saw using a small needle file.

 

[bitzer]

Terry,

I purchased a husky 460 P&C off of ebay for $22. Unbelieveable deal! It was the P&C, crank, bearings, seals, intake manifold, strato/intake boot, and AV spring. I couldn't believe it. It all looks immaculate. The 460 wears the same crankcase as the 455.

I will degree it tommorrow, but some interesting things I found. The porting looks identical to my 455 when it was stock. Exhaust is 25mm x 11mm, which is close to what the 455 was (currently the 455 is 33.5mm and 13mm or so. The Piston cut aways (above the strato cut away)are larger, longer and, have a cross-hatched pattern on them and also a hole in them closer to the intake side. Markings from the exhaust blowing down the transfers are much more apparant. There is a lot more brown "glazing" where the exhaust moves on this p&c compared to the 455. It almost seems like it is due to the holes in the cut aways. The exhaust port is also caked with carbon as is the crown and underside of the piston. I emailed the seller asking for saw history and year. I expect that the saw was stock and not messed with, but I asked him a bunch of questions. Hopefully he gets back to me and has some info. He may have nothing. It will be interesting to see where the numbers are. I believe I will do a little more testing and documenting with this one.

 

[Terry Syd]

$22!

Wow, what an upgrade. You have picked up almost 10% more displacement - and you haven't even started modding the engine.

You said the hole in the cutaway was towards the 'intake' side, are you sure it wasn't towards the exhaust side? That's where mine is on the 450, it also has that hatch pattern in that cutaway. From the description it sounds like it was run with a petroleum based oil that really built up some deposits.

The deposits in the transfers is giving more evidence of a lack of blowdown on these Husky stratos. I'll be interested to see what the timing figures are on the stock 460.

 

[bitzer]

Alright Terry here are the durations:

455
Exhaust-172
Intake-164
Transfer-140
Strato at transfers-134
Strato Intake-164
Blowdown-16*
Transfer tunnel length (shortest distance starting from crankcase opening to the blunt end of the tunnel with the covers off)-108.75mm
Intake opens 15* before strato

Stock 460
Exhaust-160
Intake-140
Transfer-135
Strato at transfers-132
Strato Intake-178
Blowdown-12.5*
Transfer tunnel length-113.2mm
Intake opens at the same time as strato

These are timed runs I made this morning in very hard, frozen 15" Black Cherry, good consistant wood through-out. I saved a 6ft section this time for milling, very pretty wood. The numbers are all averages. 24" bars were used for all. Chains were all sharpened recently, but all have seen about the same amount of work so I would say they all equal out.

455-19.5 sec
stock Husky 460-22 sec
Stihl 310 (ported)-19 sec
Stihl 390 (mild MM)-22 sec
Stihl 440/460BB (84cc ported)-12.5 sec


I was surprised at the stock 460s numbers (I have two mufflers BTW, the stock one I used for the 460s times minus the spark screen). I thought it would have been slower, but it did have a good deal of torque. I think I may have taken the 455 too far or I may need to open up the strato intake ports. I know that is how the Stihl stratos are being ported and the 441 builds that have been shown seem to have made strong gains. I don't know. I think with the 460 I will start with basic porting (exhaust to 70%, intake as wide as possible and drop maybe 5 degrees, transfers extended back toward intake) and get some numbers before I mess with the transfer durations. It looks like I shortened the transfer tunnels by almost 4.5 mm. I took about 3mm or so off of the opening to the transfer at the base and dug out a groove around the corner and along the shortest path to the top. I may have gone too far. Its hard to tell, but I won't go so low with the intake on this one. In the idle butterfly there are already indents that I widened slightly so my pooling problem is not so bad anymore. I am not sure when I will get to this build.

The seller emailed me back and said the saw came from Lowes(big box store) and he doubted that it was messed with at all. That was all he knew as he is an Echo dealer and took the saw in on trade.

I guess if you add in the 8% difference in displacement the 455 is running around 20% over stock. I should see what the stock muffler does to it. You are right the holes in the cut outs are on the exhaust side. What year is your saw? I just wonder when they made the change in design.

 

[Terry Syd]

Timing

My 450 is a 2009 model, the 50th Anniversity model.

Two-strokes with relatively more transfer timing usually have a broader powerband (at the expense of top-end power). It looks like this 460 has been ported for torque. Also, the 160 degree exhaust timing is in line with what the guys on this site have been using as an upper limit to retain torque. 140 on the intake is also low-end torque oriented.

As I understand it, this engine has the strato timing set for less than the intake timing. Perhaps the torque design required less strato timing in order to meet EPA. Did you check the strato timing with the transfer covers off? The timing begins when the piston cutaway begins to peek over the bottom of the transfer port.

Again, we have a Husky strato in the region of 12 degrees of blowdown. The design of the long transfer port tunnels must play a part in allowing these engines to run with such short numbers.

Those transfers are already very high. I would be reluctant to do anything to them, the last thing you need would be an 'opps' that decreased the blowdown even more.

Bob, you have the old piston so you could trim it for testing and then later pop in a fresh piston. Perhaps take the intake port down to about 145 duration, then start trimming the piston skirt to take it up to 155 duration. If you started to loose some of the torque you would know about what timing to set the intake for when you installed the fresh piston.

The same applies for the exhaust. If you wanted to test to see what some extra blowdown would do to the powerband, you cold trim 2 degrees off the front of the piston crown. If you lost torque, then a new piston will fix it up.

It was surprising what an extra two degrees of blowdown did for my powerband. At these low blowdown figures, a small physical change is a large percentage change.

I look forward to your testing.

 

[Terry Syd]

158 degrees

I just got back from testing the saw with the exhaust duration taken out to 158 degrees. There was a slight improvement in the upper power range, but nothing like what the first two degrees of additional blowdown gave me. I could still dog it in, but the higher cutting speed was where it was doing the best work.

I measured the exhaust duration before I started cutting and my previous exhaust duration was closer to 155 degrees rather than 154.

The saw would hit the rev limiter fairly often if I didn't have it working in the wood. However, since I now know what that sound is it doesn't bother me like it did before. I had thought the next test would be taking the exhaust out to 162 degrees, but I won't be doing that now. This saw would seem to work well with a 156-158 degree exhaust duration (the piston does have the exhaust scallops on the crown, so there is a bit more blowdown area for the timing).

I checked the plug during a high speed cut and later with it dogged in using the torque, the plug reading was about the same for both tests, so the carburetion looks good. The electrodes on the torque testing showed more heat, but down in the plug the deposits on the ceramic looked similar.

I think I will see if anyone around here can weld me up a dome on a fresh piston.

 

[AUSSIE1]

G'day Terry.
If you think you have gone a tad too far on the exhaust you could increase the transfers by a couple of degree's as this brings your torque back down and helps fatten it. Get your comp as high as you can get it.