Poulan 2150 Build Thread

[thompsoncustom]

I'll be moving on to widening the ports, lowering the intake, and raising the transfers. Any opinions and what I should do first? I would like to do it steps so that I can see what each mod does to the saw like I have been doing.
I would say widen them first. Measure the port width at the cylinder side first and figure out what percentage of the bore it is currently at. Most of the time the locator pins is the limiting factor on width but if I remember right on this cylinder it's actaully the port itself but just make sure you don't get to close to the locator pin. I'm not sure what side the locator pin is on from the factory but I would put it on the intake side if there's no interfernce.

This saw is only 36cc, not sure if that changes any of the numbers you posted. The saw has open transfers
Yes being a small saw does change the numbers somewhat. sub 50cc like higher exhaust number/lower physical and shorter blowdown but the numbers listed above are right. 106/121/75 are about prefect for that saw were a bigger one like a ms660 100/120/80 is better.

Why is blowdown important? Does the fresh charge from the intake coming in sooner help push out the exhaust and therefore make a more efficient saw?
Not sure if my thinking on that is correct.
Your chasing out spent exhaust gas sooner and more of it gets out allowing more fresh charge to get in. Looks at it this way if there is 20% left over exhaust gas in the cylinder on the next stroke that's 20% that could be air/fuel and your missing out on a 20% increase in power.
"adding volume is bad if it's not adding a bunch of air flow, having big hogged out lower transfers will make the saw lazy."
Could you explain this?
You need transfer velocity to help chase out the spend exhaust gas, like blowing through a 1/2 pipe vs a 2in one. Everything works together to make a strong saw. Lowering the intake or raising the transfers lowers case compression. To little case compression and the saw will be lazy on the low end from to low of transfer velocity. I would say stay above 45 case compression on that size saw which is the difference between your intake closing and your transfers opening.

 

[NSEric]

This next iteration all I did was rough up the intake a little bit. I saw a video on YouTube of a guy that did one of these saws and he roughed his intake. Not sure if I roughed it enough, it didn't seem to do much.

I'll be moving on to widening the ports, lowering the intake, and raising the transfers. Any opinions and what I should do first? I would like to do it steps so that I can see what each mod does to the saw like I have been doing.


Tinman's videos are definitely a good place to start for any beginner, he does say that it his method and there are lots of way to achieve the same result. No complaints with his videos.

This saw is only 36cc, not sure if that changes any of the numbers you posted. The saw has open transfers.

Why is blowdown important? Does the fresh charge from the intake coming in sooner help push out the exhaust and therefore make a more efficient saw?
Not sure if my thinking on that is correct.

"adding volume is bad if it's not adding a bunch of air flow, having big hogged out lower transfers will make the saw lazy."
Could you explain this?


Why is blowdown important? I'll pose the same question to you as I asked NSEric above.

I probably won't do the removable dome on this build but I'll eventually PM you about it.

Blow down is very important.
20 degrees is the safe number a lot of new porters use as you know it will work.
15 degrees of blow down on saws with the exhaust at 105ish works on a lot of saws. I've found you want the transfers to open at about 120 degrees atdc on most saws and if you have a smaller saw with the exhaust at 105 you have 15 degrees of blow down, if you have a big saw with the exhaust at 100 you have 20 degrees of blow down.
Opening the transfers sooner/less blow down lets the exhaust help pull the mix up out of the bottom end but if you open them too soon (like the transfers opening at 110 atdc) the exhaust will push the mix back down the transfers. Short blow down saws are very snappy because of this.

The bottom end has to compress the mixture so it will flow up through the transfers, if you make the bottom end bigger volume wise by making the lower part of the transfers wider it doesnt compress the mixture as much so it doesnt shoot it up through the transfers as fast. You need to find a happy medium between adding flow and not adding much volume.

I built a few 54cc zenoah clones(they're a very similar design as the poulan 2150), these saws have the exhaust too high and you cant fix it, 104 is better but 100 is as low as I can get it.
One has the exhaust at 98 and the transfers at 122, the other the exhaust at 100 and the transfers at 118, everything else is about the same. The saw with the transfers opening at 118 is snappier and stronger bucking large wood, the one at 98 and 122 is better for small wood as it revs higher.

 

[Homer6679]

Thanks for the information, I’ll widen the ports first and then move to working on the transfers. I’ll be on vacation till Thursday evening and probably won’t get any work done until the weekend.

In the meantime I took the saw out to cut some firewood with my pops as it currently sits and it ran and cut awesome. Definitely uses way more fuel than it did stock. Im excited to see how it will run with future modifications.

How long of bars can you run on these saws? It handled the 18” bar just fine and oiled it fine as well. If I could get a 24 on it that would be awesome.

 

[Homer6679]

Got to work on the 2150 today, I widened the exhaust and accidentally raised the exhaust on one side by 4 degrees so I just decided to raise the whole port by that amount.

I was running the saw and the saw seems much more difficult to tune. Almost like each turn of the H/L screws seems more touchy. The chain was dull so I’ll get a video of it running and cutting tomorrow as well as a comp reading hopefully.

My thinking is that because I’ve opened up the exhaust so much added a ton of flow the intake can’t match it. For instance, the prior intake charge plus the back pressure was matched to the cfm flow rate of the exhaust port therefore creating a smoother/better running engine. Now that the exhaust port is wider and higher it flows more cfm so now in theory I have more room for intake charge. In other words my exhaust is outrunning my intake. I’m not sure if that really makes a difference or if that line of thought is even correct. Some input would be appreciated.

My first thought to remedy this issue is to raise the transfers by the same amount I raised the exhaust. I don’t have very much play room with raising the intake port.

 

[thompsoncustom]

Got to work on the 2150 today, I widened the exhaust and accidentally raised the exhaust on one side by 4 degrees so I just decided to raise the whole port by that amount.

I was running the saw and the saw seems much more difficult to tune. Almost like each turn of the H/L screws seems more touchy. The chain was dull so I’ll get a video of it running and cutting tomorrow as well as a comp reading hopefully.

My thinking is that because I’ve opened up the exhaust so much added a ton of flow the intake can’t match it. For instance, the prior intake charge plus the back pressure was matched to the cfm flow rate of the exhaust port therefore creating a smoother/better running engine. Now that the exhaust port is wider and higher it flows more cfm so now in theory I have more room for intake charge. In other words my exhaust is outrunning my intake. I’m not sure if that really makes a difference or if that line of thought is even correct. Some input would be appreciated.

My first thought to remedy this issue is to raise the transfers by the same amount I raised the exhaust. I don’t have very much play room with raising the intake port.

Well a couple things:

Your exhaust should always out run your intake that's normal and wanted you can't get any more air in than you can get out, your case charge is compressed as soon as the piston clears the floor of the intake and that pressure is released as soon as the transfers open and your charge comes flying in as long as the pressure is low enough that it's not back stuffing the exhaust. When you raise the exhaust saws become high rpm and peaky meaning they run in a much narrower power band and lose torque so if your cutting small wood it will cut faster big stuff will be slower. They also become harder to tune.

Look at it this way from TDC to when the exhaust port opens that's your power stroke and all your power is transferred here so by raising the exhaust your shorting the amount of power transferred to the crank but you also lower the compression stroke (and actually compression) so it's easier for the engine to overcome going up and you pick up rpms.

You are right now you can widen/lower your intake to stuff more charge in there no need to raise the intake and your correct again that raising your transfers will also help.

But speaking from experience I would start on a different cylinder at this point in a little saw like this you never want to raise the exhaust roof. But you could keep going and learning what your changes do it's good experience either way.

 

[Homer6679]

Look at it this way from TDC to when the exhaust port opens that's your power stroke and all your power is transferred here so by raising the exhaust your shorting the amount of power transferred to the crank but you also lower the compression stroke (and actually compression) so it's easier for the engine to overcome going up and you pick up rpms.

This is a very good explanation.

So would you say in general to overcome the loss of torque or in other words a shorter “power stroke” caused by raising the exhaust you need to up compression by means of removing base gasket/lathe work or raising the transfers?

Or does the compression not matter to a certain extent. Obviously it needs comp to run but with 150psi will it produce more torque than 130psi? For instance, 130 vs 150psi will still only transfer “x” amount of power over the “x” amount of degrees to when the exhaust opens.

 

[thompsoncustom]

You pretty much nailed it there. Yes compression is how you would help with the shorter power stroke but you can't get back the time in which that power is applied. Little saws like a lot of compression 250psi is common in some modded 50cc saws.

Raising the transfers also helps because now that the exhaust is higher the cylinder pressure drops sooner so you can start getting fresh charge in there earlier.

I am currently working on a way to easily up compression in clamshells using a ceramic adhesive in the combustion chamber but haven't figured it out yet. and I'm not trying to sell ya something if I get this figured out it will be free information for everyone.

 

[NSEric]

Got to work on the 2150 today, I widened the exhaust and accidentally raised the exhaust on one side by 4 degrees so I just decided to raise the whole port by that amount.

I was running the saw and the saw seems much more difficult to tune. Almost like each turn of the H/L screws seems more touchy. The chain was dull so I’ll get a video of it running and cutting tomorrow as well as a comp reading hopefully.

My thinking is that because I’ve opened up the exhaust so much added a ton of flow the intake can’t match it. For instance, the prior intake charge plus the back pressure was matched to the cfm flow rate of the exhaust port therefore creating a smoother/better running engine. Now that the exhaust port is wider and higher it flows more cfm so now in theory I have more room for intake charge. In other words my exhaust is outrunning my intake. I’m not sure if that really makes a difference or if that line of thought is even correct. Some input would be appreciated.

My first thought to remedy this issue is to raise the transfers by the same amount I raised the exhaust. I don’t have very much play room with raising the intake port.

4 degree's is close to 1 mm, how did you raise it that much by mistake?
These are tiny cylinders and ports, you dont need to grind much at all.
If you're having issues controlling how much you're grinding off the ports, try less aggressive bits so you dont over port it again.
All joking aside you can port an exhaust or intake port with a diamond bit for sharpening chains and do a decent job and it wont take too much off really quickly like a burr can.

 

[Homer6679]

4 degree's is close to 1 mm, how did you raise it that much by mistake?
These are tiny cylinders and ports, you dont need to grind much at all.
If you're having issues controlling how much you're grinding off the ports, try less aggressive bits so you dont over port it again.
All joking aside you can port an exhaust or intake port with a diamond bit for sharpening chains and do a decent job and it wont take too much off really quickly like a burr can.

Inexperience perhaps causes the most amount of stupid tax lol

 

[Homer6679]

I did some porting on the transfers of the initial cylinder and noticed a difference in tunability and torque while cutting. Overall a much smoother saw but I wasn't satisfied with the results however. Long story short, it cut pretty slow when the bar was buried.

I went ahead and ported an extra cylinder I had and the timing numbers are stock except for the transfers. I also added dimples to the intake similar to a golf ball to see if the science behind golf balls may apply here as well. That was the best I could do with the bits I had on the transfers. My port work here was much better and I'm satisfied with it for my second port job ever.

I will do test cuts tomorrow with it and take a video as well.

 

[Homer6679]

Attached is the video of the setup pictured in post #30 directly above.

Definitely a Stronger saw than stock but I think the exhaust is to low. A previous version of the saw had the exhaust at 104 and cut faster than it is right now. My deflector for my exhaust came off so there is less back pressure as well.

I will take a new video of the saw cutting tonight or tomorrow once I fix up the issues mentioned above.

 

[thompsoncustom]

I did some porting on the transfers of the initial cylinder and noticed a difference in tunability and torque while cutting. Overall a much smoother saw but I wasn't satisfied with the results however. Long story short, it cut pretty slow when the bar was buried.

I went ahead and ported an extra cylinder I had and the timing numbers are stock except for the transfers. I also added dimples to the intake similar to a golf ball to see if the science behind golf balls may apply here as well. That was the best I could do with the bits I had on the transfers. My port work here was much better and I'm satisfied with it for my second port job ever.

I will do test cuts tomorrow with it and take a video as well.

How wide is your exhaust port of the bore side?

 

[scottr]

Homer , did you close the rear louver muffler outlets when you made the big side outlet ?
Scott

 

[Homer6679]

How wide is your exhaust port of the bore side?

The usable bore is 1.9”, my current exhaust port is .95” or about 50%.
I am going to widen the exhaust to 1.24” or 65%.

I am also going to widen the Intake, one side is limited because of the locator pin. The other side I’m going to widen a little bit by .18” and I will lower the intake by a couple degrees.

I have some longer burrs coming today so I will do some better work on the transfers as well

Homer , did you close the rear louver muffler outlets when you made the big side outlet ?
Scott

I just taped them flat with a hammer. I have some pictures attached.


I raised the exhaust to 103 and it cuts about the same. So no need for a new video.

 

[Reesedlightning]

I did a 36cc craftsman version of your saw a while back and ended up at
Ex 105 but more of a square roof
Trans: 121 with small fingers coming off that open at 120
In: 74 but wide with a square floor that becomes more oval up top.

The thing rips compared to stock.

Something to note, when it comes to port size, area can equal time. I have run some seriously fast saws that have a low exhaust roof. I have also put together two of the same saw with the same numbers, but completely different port shapes and gotten completely different results. Just because you hit the numbers, doesn’t mean it’s going to rip. Took me a good bit of trial and error to figure that out.
I too learned a lot of stuff from Tinman. I must have watched his video series about 10 times and then all of his other informative videos. I agree with Tompsoncustom. Having ported about a dozen saws or so, I’m starting to realize Tinman leaves a lot on the table and he doesn’t do a lot of small stuff.
It seems like you’re on the right track though. Just because it’s a clamshell, doesn’t mean you can’t make it rowdy.
These saws seem to like 15-16° blowdown.

 

[Homer6679]

I did a 36cc craftsman version of your saw a while back and ended up at
Ex 105 but more of a square roof
Trans: 121 with small fingers coming off that open at 120
In: 74 but wide with a square floor that becomes more oval up top.

The thing rips compared to stock.

Something to note, when it comes to port size, area can equal time. I have run some seriously fast saws that have a low exhaust roof. I have also put together two of the same saw with the same numbers, but completely different port shapes and gotten completely different results. Just because you hit the numbers, doesn’t mean it’s going to rip. Took me a good bit of trial and error to figure that out.
I too learned a lot of stuff from Tinman. I must have watched his video series about 10 times and then all of his other informative videos. I agree with Tompsoncustom. Having ported about a dozen saws or so, I’m starting to realize Tinman leaves a lot on the table and he doesn’t do a lot of small stuff.
It seems like you’re on the right track though. Just because it’s a clamshell, doesn’t mean you can’t make it rowdy.
These saws seem to like 15-16° blowdown.

In simpler terms when you say that area can also equal time. I assume you are saying that if you widen your port by “x” amount it would be equal or have the same effect of raising/lowering by “x” amount?

What port shapes did you notice worked better/had the most performance gains?

 

[Reesedlightning]

To a certain extent, yes.

I tend to like a more square opening on my ports. It provides a more abrupt opening allowing a larger volume of air to start moving sooner. Whereas an oval port Will start to gradually release exhaust or in the case of an intake, will gradually allow air to start moving in. Something to note with an intake, there is a point of no return with widening. If you go to wide, you will lose velocity. So there’s a balance between opening it enough to allow more air, but not so much that you start to lose the velocity. generally, I will leave the outside opening alone and not widen the inside more than that. It can get tricky because it does vary from saw to saw but you’ll get the feel of it. The downside to a port, that is wide and square is that it can make it harder on the piston rings over time. But as long as you pay attention to your port chamfer, and don’t go crazy wide, you will be fine. Charles Briscoe has some good, no bs porting advise on YouTube.

 

[Reesedlightning]

Here are a couple of pictures from an album I have. I did it a 029 super to 039 conversion for a friend and went with flatter ports and it’s runs better than my personal 039.
And then there are some pictures of an ms170 I did which has a very similar cylinder to the poulan 36cc.
I’m not saying that it’s the best way and there are a lot of other folks here that will say something different but I have found it works really well for me. I got the idea from some good builders on here and the other site.

 

[Homer6679]

Very good photos, thanks for sharing. I’ll have to play around with the port shapes and take some notes on the characteristics they cause.

I noticed on the intake they are rough. What is the reasoning for that? And how rough are they?

 

[thompsoncustom]

In simpler terms when you say that area can also equal time. I assume you are saying that if you widen your port by “x” amount it would be equal or have the same effect of raising/lowering by “x” amount?

What port shapes did you notice worked better/had the most performance gains?

I raised the exhaust to 103 and it cuts about the same. So no need for a new video.

Always widen your ports before raising them going forward.

It's not that widening them equals the same as raising or lowering them and how it performs but if you have a port that is to small you can increase flow by either increasing area (widen) or time (duration) or both of course.

So for example before raising your exhaust if you widened it to 65% or 70% of the bore you could increase flow without giving up any torque.

Port shape like mentioned makes a big difference in how it performs also with a flatter exhaust roof producing more power but at the cost of the ring life sometimes. On the intake port you can have the bottom of the port 100% square without causing problems because the rings don't travel that far down. Rough intakes are to increase atomization of the fuel and polished exhaust don't really help flow but do help with carbon build up.

Another thing to measure is your total muffler opening vs the exhaust port size on the bore side. Hard spaghetti actually works really well for this. If your trying to match 100% of your exhaust port you just fill it in with the hard spaghetti and then take those pieces and put them in your muffler ports or make the ports bigger till they all fit. Also easy to use them with a little math if you want to go to 125% or more.