Part Three: The Transfer Ports

[Ketchup]

I would love to see what that crank mod looks like

I didn’t know much about saws then. I took photos, but my phone encountered the tire tread of our chip truck and they were lost.

It was a bit of a hack job. I could probably do something similar with a flat file. It appeared that the saw never really ran after the mod. The rings and con rod bearings were full of metal shavings. Everything was scratched all to hell. Not pretty. The idea has merit though.

 

[Fruecrue]

I’m not sure notches on the crank would have a positive impact other than lightening of the rotating mass.
Any void moving that fast would probably just create a vortex like the open bed of a pick up truck. Whatever fluid is contained therein would just swirl and create a boundary layer for other fluid to slide across it and not mix.
If on the other hand, notches were cut into the sides, similar to the veins on a flywheel, they would impart velocity on the surrounding fluid which translates to differential pressure between its axis and the case which would serve as a volute. Any energy imparted on said fluid would come at the cost of adding drag to the crank. Any gain would need to overcome that energy loss before it could be appreciated at the power take off. My mind wonders if this would also starve the crank bearings of oil.
Just my thoughts anyhow.

 

[Mastermind]

I’m not sure notches on the crank would have a positive impact other than lightening of the rotating mass.
Any void moving that fast would probably just create a vortex like the open bed of a pick up truck. Whatever fluid is contained therein would just swirl and create a boundary layer for other fluid to slide across it and not mix.
If on the other hand, notches were cut into the sides, similar to the veins on a flywheel, they would impart velocity on the surrounding fluid which translates to differential pressure between its axis and the case which would serve as a volute. Any energy imparted on said fluid would come at the cost of adding drag to the crank. Any gain would need to overcome that energy loss before it could be appreciated at the power take off. My mind wonders if this would also starve the crank bearings of oil.
Just my thoughts anyhow.

You sound smart.

Can I get your autograph?

 

[Fruecrue]

You sound smart.

Can I get your autograph?

Yup.
How’s your pig situation?

 

[Mastermind]

Yup.
How’s your pig situation?

Festering.

 

[Stump Shot]

Festering.

 

[cus_deluxe]

Pulled a saw apart once that had notches cut into the crank weights. The notches were tapered and aimed at the transfer lowers.

Anybody else seen this? Could it help transfer velocity? Is it worth the extra resistance?

ive heard of that type of mod called a “turbo” crank. an old mechanic i know talked about a guy who did it on snowmobiles or something. didnt sound like it was a real gain of any kind, but the guy swore by it apparently.

 

[Nutball]

Some rc car engines use it, but they are rated for 48-60krpm, and have the transfers in line with the crank weight

 

[Ketchup]

I’m not sure notches on the crank would have a positive impact other than lightening of the rotating mass.
Any void moving that fast would probably just create a vortex like the open bed of a pick up truck. Whatever fluid is contained therein would just swirl and create a boundary layer for other fluid to slide across it and not mix.
If on the other hand, notches were cut into the sides, similar to the veins on a flywheel, they would impart velocity on the surrounding fluid which translates to differential pressure between its axis and the case which would serve as a volute. Any energy imparted on said fluid would come at the cost of adding drag to the crank. Any gain would need to overcome that energy loss before it could be appreciated at the power take off. My mind wonders if this would also starve the crank bearings of oil.
Just my thoughts anyhow.

I was thinking a lot of the same things. I don’t think it would have much effect on oiling the bearings.

The saw I took apart was an open port clamshell. I could see more application for a bottom fed transfer (461, 201 come to mind). I feel like the timing of transfer opening relative to crankweight position is an important factor.

Crank weight loss and case volume increase are also something to consider. Still thinking about it.

 

[stinkbait]

I think that the original thought was applied to full circle cranks. I dont see how you could make it work with your normal chainsaw crank.

Sent from my SM-G930V using Tapatalk

 

[Billy Currie]

There seems to be a consensus here that quad ports require more blow down than dual port. Delete this if I throw too much out there, but is it because the quad ports are closer to the exhaust port and would scavenge too much from the transfers? I would have to link 2 things that contribute to determining the amount of blow down..... 1) the distance between the exhaust port and transfers and 2) the angle that the transfer ports favor forcing the air-charge into the cylinder. It would all be relative to how much air-charge would be lost out of the exhaust port.

So a quad port would benefit from an angle that would direct the air-charge more to the rear of the cylinder......if it is indeed closer to the exhaust port. Continuing on that theory, a transfer port close to the exhaust port may also benefit with a reduced window size, or a tapper that would increase the velocity in that area projecting the air-charge away from the exhaust port. While other transfer ports at the rear of the cylinder could be of a design with a lower velocity. However, it would be necessary to have the transfers closer to the exhaust open first and close last to keep the air-charge from the rear transfers in the cylinder for combustion.

Or am I an idiot?

 

[huskihl]

There seems to be a consensus here that quad ports require more blow down than dual port. Delete this if I throw too much out there, but is it because the quad ports are closer to the exhaust port and would scavenge too much from the transfers? I would have to link 2 things that contribute to determining the amount of blow down..... 1) the distance between the exhaust port and transfers and 2) the angle that the transfer ports favor forcing the air-charge into the cylinder. It would all be relative to how much air-charge would be lost out of the exhaust port.

So a quad port would benefit from an angle that would direct the air-charge more to the rear of the cylinder......if it is indeed closer to the exhaust port. Continuing on that theory, a transfer port close to the exhaust port may also benefit with a reduced window size, or a tapper that would increase the velocity in that area projecting the air-charge away from the exhaust port. While other transfer ports at the rear of the cylinder could be of a design with a lower velocity. However, it would be necessary to have the transfers closer to the exhaust open first and close last to keep the air-charge from the rear transfers in the cylinder for combustion.

Or am I an idiot?

I haven't noticed quad ports wanting more blowdown. Some 346's run really well on 12-14°. Seems to have way more to do with how the engine was designed to run.

 

[Billy Currie]

I haven't noticed quad ports wanting more blowdown. Some 346's run really well on 12-14°. Seems to have way more to do with how the engine was designed to run.

Reading the entire thread, it looked like a few others had experienced the need for more blow down on the quad ports, but if that's not the case then what I have mentioned has been disproven.

 

[huskihl]

Reading the entire thread, it looked like a few others had experienced the need for more blow down on the quad ports, but if that's not the case then what I have mentioned has been disproven.

Idk. Just my experience. Case capacity and desired rpm/hp/torque seem to dictate where I end up. But it may certainly be true for someone else. No 2 builders do the same thing intentionally

 

[Nutball]

Sounds like it's time to experiment?

 

[MustangMike]

I have never ported a quad port cylinder, but I do like to install bridge ports!

I also have not ported enough of them to have firm conclusions, but my observations are as follows: (and I fully welcome comments from anyone with more knowledge)

It seems like less blow down likes more open mufflers,

It seems like longer stroke engines prefer lower exhaust and intake.

 

[Nutball]

I noticed when rinsing a 201tc cylinder than the intake side transfer ports barely let any water out while the exhaust side transfers took >90% of the flow. Of course water acts differently, but it makes you wonder how well it works with high speed pressurized air

 

[Billy Currie]

I cannot find where this has been covered. There are a few different designs of piston windows that aid in feeding the transfer ports. I've been selecting pistons with a wider skirts to favor a wider intake port, but I may have been overlooking the window layout that is better suited for feeding the transfer ports. See pictures:

There are others, but not many. I don't know that the window shape is as important as just having a clean open path: clean up rough areas with a dremal and make sure the window matches the transfer opening with good transition. But these pistons are for the same saw, a Husky 266. What would make one of the pistons really stand out from the others?

 

[Mastermind]

I cannot find where this has been covered. There are a few different designs of piston windows that aid in feeding the transfer ports. I've been selecting pistons with a wider skirts to favor a wider intake port, but I may have been overlooking the window layout that is better suited for feeding the transfer ports. See pictures:
View attachment 218224 View attachment 218225 View attachment 218226
There are others, but not many. I don't know that the window shape is as important as just having a clean open path: clean up rough areas with a dremal and make sure the window matches the transfer opening with good transition. But these pistons are for the same saw, a Husky 266. What would make one of the pistons really stand out from the others?

Flow....or velocity? RPM or torque?

And so on.....

 

[Stump Shot]

I cannot find where this has been covered. There are a few different designs of piston windows that aid in feeding the transfer ports. I've been selecting pistons with a wider skirts to favor a wider intake port, but I may have been overlooking the window layout that is better suited for feeding the transfer ports. See pictures:
View attachment 218224 View attachment 218225 View attachment 218226
There are others, but not many. I don't know that the window shape is as important as just having a clean open path: clean up rough areas with a dremal and make sure the window matches the transfer opening with good transition. But these pistons are for the same saw, a Husky 266. What would make one of the pistons really stand out from the others?

A member turned me on to switching styles from the old OEM full circle style on top, to the newer 268xp closed port/open window style on the bottom. This made the 266 more sporty with no other changes. The top one does have more stability in the bore, if that's a consideration at all. The middle one is really a slab sided 268 open port design and I can't say that I have tried it in the 266 to say anything one way or the other, never really thought about it. I do like and build 266's with the full window piston in the bottom picture.