Part Three: The Transfer Ports

[Adirondackstihl]

Well it looks great.

 

[Mastermind]

Not you........the 346 jug and slug. lol

 

[Stump Shot]

In my humble opinion, there is nothing more important to performance than the relationship between the three ports that we are discussing.

That means blowdown, and case compression time.

Elaborate please, my skull is surely thicker than yours and can barely see the lines. Lol I can see how one is positively connected to the other, what's the compromise?

 

[Moparmyway]

Well it looks great.

Welp, it had great mid range torque, but not enough on the high end. I'd have left it alone if it was going to be a work saw, but I'm looking at this as a play saw. I've since hogged out the lowers , and moved peak power up in the rpm's and lost some of the mid range torque it had.

I was hoping to get more of an opinion from you on it though ......... good or bad

 

[Mastermind]

Elaborate please, my skull is surely thicker than yours and can barely see the lines. Lol I can see how one is positively connected to the other, what's the compromise?

I have theories. Sometimes unproven. lol

I think quad ports need more blowdown than dual ports. I think a less restrictive muffler works best with shorter blowdown.

I think case compression needs to be balanced so that the transfers flow hard at the opening point.......but it can't be so high that it causes pumping losses.

Every engine is different though. Sometimes it takes me a bunch of tries to really find that balance that makes it really wake up.

 

[Stump Shot]

Well it looks great.

I did a similar, but not as extensive job to the piston of the 51 as Moparmyway did to his to let the charge get into the open ports easier. And yes the job on that 346 does look great. I did do a report on the RPM of that saw for you like you asked boss...

 

[Chainsaw Jim]

I think we grind out a lot of engineered goodness the factory gave us in the name of flow. The first thing we all have done is open the hell out of the lowers. I think the best flow will be when the duct is even sized the whole way through.

I believe the transfer design in the 346/357/372 and stihl 361 and the new echos are just about optimized. then they come out with the stratos and change the whole game.

It's a popular belief that chainsaw engineers are all knowing gods, but they actually have several people telling them how to do their job... including the epa. They also need to make the design in a way so high scale production casting can replicate it without a considerable amount of additional machine work.

None of those obstacles apply to us. Most of those engineers are building race saws on the side for fun and that's where you'll see how they compare to our end of this industry. I've noticed some pretty mixed reviews in the past over some of the examples.

 

[Mastermind]

I was hoping to get more of an opinion from you on it though ......... good or bad

My ideas don't mean much to anyone but me. I've seen some guys open everything way up, and go fast as hell. I never build fast saws though.....

The strongest running 346 I've ever seen was one that beat the crap out of every saw that ran against it.......and there were a hell of a lot there that day. It was completely untouched in the bottom transfers. That made me really rethink a lot of stuff. Maybe for every grain we take out of the bottom, we lose a little of transfer to the combustion chamber? But then how do these hogged out saw go like a mfer?

I didn't comment because I don't want to be responsible for misleading you. You gotta test....and test.

 

[Chainsaw Jim]

Case volume low or charge getting lazy because charge isn't large enough?

 

[Deets066]

OK.......

Now let's talk about the transfer ports

 

[Deets066]

I'll have to read through this one when I get home

 

[Hedgerow]

Ya need more area to flow more stuffs..
But if ya got limited stuffs, what the hell good is the ability to move more of it??

Or:
You can focus on just moving your limited stuffs more efficiently.

But that has limits and isn't much fun.

 

[Stump Shot]

I have theories. Sometimes unproven. lol

I think quad ports need more blowdown than dual ports. I think a less restrictive muffler works best with shorter blowdown.

I think case compression needs to be balanced so that the transfers flow hard at the opening point.......but it can't be so high that it causes pumping losses.

Every engine is different though. Sometimes it takes me a bunch of tries to really find that balance that makes it really wake up.

OK, what would you consider to be a long blow down, and what would a short one be? Ya, the long and the short of it, that's it.

Also consider that I'm mostly working with old 2xx and 0xx series saws with closed ports and windowed pistons, you know the kind - junk. Lol Also not looking for the gains that you good porters are realizing, my goal is to make awesome firewood saws for people that can't afford to buy a new pro saw. So all that leaves is old pro saws, that need a little boost to get close to the modern level. With what I'm doing now saws are good people are happy, would like just a little bit more to make them really happy. It's pretty much all about the smiles.

 

[RIDE-RED 350r]

I think that with transfers, we should definitely be careful not to hog things out too much in the interest of maintaining transfer velocity. If velocity drops too much, fuel doesn't stay atomized well. Flow is obviously good too, but only to that point where displacement and case volume/compression can adequately support it. I have no idea how to calculate case volume to make an informed decision on how much or even if the transfers would benefit from being enlarged. So I'll stay tuned for more folks to chime in on that subject.

One thing I have an idea on is this: I think in my mind that most saws would probably benefit from matching the lowers to the case (talking about cylinders with lowers like a 346, 357, 372 here) but I'm not sure if it would always work to significantly enlarge them all the way up through to the port windows themselves. I think of it like creating something of a venturi effect as the transfer tunnel comes around to the transfer port window itself. Low restriction from the case to the lowers and as they taper down I would think that might accelerate the transfer charge as it reaches the transfer window. We gain area by raising them if we do so, but so far on my saws I have ported I stopped at just raising them and did not widen them at all. I could very well be off in my thinking on this theory, but my saws came out well doing it that way.

 

[Stump Shot]

Ya need more area to flow more stuffs..
But if ya got limited stuffs, what the hell good is the ability to move more of it??

Or:
You can focus on just moving your limited stuffs more efficiently.

But that has limits and isn't much fun.

You're a really good explainerer.

 

[old guy]

I'm getting a headache.

 

[RIDE-RED 350r]

Randy, I'm interested in your theory that quads need more blowdown than duals. Can you elaborate on this idea??

My thought and not to get back on the subject of exhaust that has already been covered, but I think that maximizing exhaust flow reduces the amount of minimum blowdown for good transfer action. However, my 394 is running 18 degrees of blowdown and it seems to run quite strong. Being dual port, I wonder if that is proof that your theory is sound??

 

[Stump Shot]

When I worked on the transfers of the open ported 51 I reckoned that more volume was not needed with the small of an intake track that it has. So with a very small diameter cutter, went in and rounded that sharp inside angle and smoothed the shape of the open angle. My thinking was it would allow a better circulation of the fuel/air charge to swirl toward the intake side like it was trying to be directed in the first place. Was this a good idea, or just a waste of time?

 

[Barneyrb]

Years ago a guy brought me a pair of heads to put on his engine and they had been ported with a machine that flowed an abrasive slurry through them. One of the nicest port jobs I'd ever seen (before CNC) and I've always wanted to try that with a saw especially in the transfers, I forgot the name of the process but it wasn't cheap.

 

[Deets066]

Ya need more area to flow more stuffs..
But if ya got limited stuffs, what the hell good is the ability to move more of it??

Or:
You can focus on just moving your limited stuffs more efficiently.

But that has limits and isn't much fun.

You explain it so simple and clear