Preparing to port first saw - which one, and what method?

[Sloughfoot]

Stock they were about 103 I believe on the exhaust and only 10–11° of blow down. They would cut very fast at a narrow RPM range but didn’t like to be lugged down at all or they would fall off the pipe

I wouldn't have ever thought a saw could run at all with that amount of blowdown.

 

[jacktheripper]

I went out today and dropped three trees in the mountains with the newly ported 272xp. One of them was a 24”+ standing dead rock solid pine. Blocked everything up into 14” lengths. Amounted to roughly a little less than a cord.

By the final tree, I could tell that the saw was waking up a decent amount. That was midway through the second tank…

So I got home and checked compression and squish again. Saw only blew 155psi, and that is with a measured .018 squish. The ring in it is an almost brand new caber, installed on the saw only about three tanks ago.

I think this ring needs to break in still. This might be one of those saws that takes like 10+ tanks to wake up.

 

[Stump Shot]

That makes sense. It sounds like I may benefit from a couple less degrees of blowdown (raise my uppers a couple degrees) to gain rpm in the cut. It sounds like this could come at the expense of some lugging power (dogged in torque), but may cause the saw to run faster while self feeding in its power band.

Think of things simply to visualize the answer, as in the case of blowdown, as an analogy, after exhaling a breath fully, does keeping your mouth open longer, exhale any more spent air? As for your uppers think of exhaling with a pursed lip vs exhaling through a more open mouth, which happens faster? Now try and do the same but running at full speed, you won't be able to with a pursed lip as it won't provide enough air for the body to function.
This may seem silly but is the reason why we need to think about transfer ports in duration to get a handle on how much it can feed the cylinder and fill it properly full without spilling into the exhaust before it's closed.
In the end, if you keep track of your numbers well, including duration, your particular porting style will lead you to where you should be. For now, if you can go back in the saw and try again, great, if not, take the improvement you made as a win and go at your next attempt with what you learned and try, try again. Even if you completely fail, you at least learned what not to do, and don't feel bad as there are literally millions of possible outcomes of volumetric efficiency outcomes when porting a saw when you get right down to it, so be patient and persistent heading to the goal line that none of us ever cross, but first and goal at the one yard line is a pretty good place to be.

 

[Stump Shot]

I wouldn't have ever thought a saw could run at all with that amount of blowdown.

The internet would break if the true possibilities were displayed...

 

[Sloughfoot]

Think of things simply to visualize the answer, as in the case of blowdown, as an analogy, after exhaling a breath fully, does keeping your mouth open longer, exhale any more spent air? As for your uppers think of exhaling with a pursed lip vs exhaling through a more open mouth, which happens faster? Now try and do the same but running at full speed, you won't be able to with a pursed lip as it won't provide enough air for the body to function.
This may seem silly but is the reason why we need to think about transfer ports in duration to get a handle on how much it can feed the cylinder and fill it properly full without spilling into the exhaust before it's closed.
In the end, if you keep track of your numbers well, including duration, your particular porting style will lead you to where you should be. For now, if you can go back in the saw and try again, great, if not, take the improvement you made as a win and go at your next attempt with what you learned and try, try again. Even if you completely fail, you at least learned what not to do, and don't feel bad as there are literally millions of possible outcomes of volumetric efficiency outcomes when porting a saw when you get right down to it, so be patient and persistent heading to the goal line that none of us ever cross, but first and goal at the one yard line is a pretty good place to be.

excellent!

 

[Fabulous]

I think guys overthink the blowdown - yes you need a certain amount of time to get the exhaust evacuated and this time decreases as the rpm increases (port time / area calculations) … it’s not the be all end all when it comes to performance! An example: modding your muffler properly on a stock saw shows nice gains in torque and thus ultimately hp - did you adjust the transfer heights ? No , yet the saw performed noticeably better. Taken a step further a “pipe” can outdo even the best canned muffler albeit with increased noise. If you’re new to porting I wouldn’t go raising the transfers at all! Clean them up and optimize flow direction will yield usable gains. You block off the de-comp … 2% , mill the cases or deck the cylinder … 5% , modify the squish band 4% , put in a good flowing muffler or pipe … 7 up to 25% (562xp just LOVES a pipe or healthy muffler mod) - work the “restrictions” in the intake or add a velocity stack … 5-10% — add all these together and you’ll have a good runner with boatloads of torque and there will be even more gains to be had once you go cylinder (if desired). Little things make big differences … Often overlooked, The CHAIN is important too!

 

[Sloughfoot]

The internet would break if the true possibilities were displayed...

I haven't seen bunches of them , but the work saw recipes from you accomplished porters I have found are very similar as far as timing and duration, regardless of displacement, bore, stroke length. Intake, high 70s to low 80s. Exhaust, 100 to 104. Transfers, 120 to 124. Blowdown, 20 to 24. I'm sure there are exceptions, but not many.
The few saws I've ported are in those ranges and each have the same mannerisms. A lot more power applied somewhat equally to speed and torque.

 

[Ketchup]

I went out today and dropped three trees in the mountains with the newly ported 272xp. One of them was a 24”+ standing dead rock solid pine. Blocked everything up into 14” lengths. Amounted to roughly a little less than a cord.

By the final tree, I could tell that the saw was waking up a decent amount. That was midway through the second tank…

So I got home and checked compression and squish again. Saw only blew 155psi, and that is with a measured .018 squish. The ring in it is an almost brand new caber, installed on the saw only about three tanks ago.

I think this ring needs to break in still. This might be one of those saws that takes like 10+ tanks to wake up.

Cabers take 5-10 tanks to break in, but if you’re at 155 you probably won’t hit 170 after break-in.

 

[Sloughfoot]

Cabers take 5-10 tanks to break in, but if you’re at 155 you probably won’t hit 170 after break-in.

What's the usual, around 10lb increase?

 

[jacktheripper]

Also, I’m at roughly 6000 feet. So that 150 psi comes out to roughly 176 at sea level

 

[jacktheripper]

Cabers take 5-10 tanks to break in, but if you’re at 155 you probably won’t hit 170 after break-in.

I just ran the saw today for another tank. Dropped two 25”+ standing dead pines and blocked them and limbed them. The saw started to feel like it was breaking in a bit more. When I got home, I pulled it over a few times when I was blowing the dust off. It felt significantly stronger. So I tried to start it. When I pulled it over, the starter kicked back on me hard. That’s the first time it’s done that so far. I just hooked a compression gauge to it and it blew 165, so it gained 10psi in just a tank. With the machine work and tight .018 squish, I have reason to believe that it will continue to gain compression. It certainly feels like it gained more than 10 psi, but I can’t argue with the gauge.

 

[Ketchup]

The elevation factor is significant. Great to hear it tightened up.

Kickback is often from ignition timing. Did you advance it?

 

[Sloughfoot]

The elevation factor is significant. Great to hear it tightened up.

Kickback is often from ignition timing. Did you advance it?

Will the case loading up cause kickback, or make it feel like it's kicking back?

 

[jacktheripper]

It’s most definitely from the advanced timing. And I’m not complaining about it either. But without decent compression, you won’t experience the phenomenon. At least I didn’t until it broke in a bit from use yesterday. That gives me some hope!

 

[Sloughfoot]

It’s most definitely from the advanced timing. And I’m not complaining about it either. But without decent compression, you won’t experience the phenomenon. At least I didn’t until it broke in a bit from use yesterday. That gives me some hope!

Most definitely amplifies kickback. All my runners have a timing advance and kickback. Much less kickback on the one that hasn't been ported. The most kickback on the one with highest compression. The nonported one with the least kickback never did it before a timing advance.

 

[Outback]

That's how you know you set it right.

 

[Sloughfoot]

That's how you know you set it right.

truth

 

[Ketchup]

Will the case loading up cause kickback, or make it feel like it's kicking back?

Good question. I don’t think so.