Fingers and Bridge ports

[Sty57]

Now that there is a place to be able to ask questions and not get beat up.

Can you guys talk about how Finger and bridge ports work and the theory behind them.
I think a lot of people have a good understanding of them, but I want the know how and why they work.
Thanks

 

[Stihl working Hard]

+1 on that one to Brian

 

[Warped5]

 

[czar800]

 

[Magic_Man]

Yep

 

[Deets066]

Results will be different for each saw. If you have enough velocity to use them they can be beneficial. If you have a low/large intake then it's iffy if they would help or hurt.

They work by directing the flow of the fuel charge toward the intake side. Which should aid in pushing out the burnt gasses. Also the more of the fuel charge you can put on the intake side a less amount of charge would get carried out with the exhaust before it is burnt.

 

[Sty57]

So you are trying to direct / add the charge to the Intake side without hogging out the transfers and losing velocity?

 

[Mastermind]

I'm not really all that book smart.....I'm just pretty good at copying what I've seen other people do. So, I can't even begin tell you exactly how this stuff works.

I will gladly tell you how I began using bridge and finger ports.

Dennis Cahoon and I were talking about saw parts that he had piled up one day, and he said he had some jugs he was gonna send to me.

Sure enough, in a few days a box showed up with a bunch of jugs in it.

One of them was a 064 jug that Dennis had ported. He told me that he was falling timber when he built that saw, and during the week it was his work saw, but on the weekends, he used it to race.

The saw had finally suffered a bearing failure, and the squish band was full of metal bits. Dennis dropped the jug in a box and forgot about it for a long while.

We talked again, and he told me to study that jug, and see if I could learn anything from it. So.....I cleaned it up, and gave it a good hard look.



I can tell you what Dennis told me about finger and bridge ports. What he said was very simple. The more transfer you can get around the piston, the power you can make.

 

[czar800]

I find this stuff very interesting! Is one finger higher than the other?

 

[Deets066]

I'm not really all that book smart.....I'm just pretty good at copying what I've seen other people do. So, I can't even begin tell you exactly how this stuff works.

I will gladly tell you how I began using bridge and finger ports.

Dennis Cahoon and I were talking about saw parts that he had piled up one day, and he said he had some jugs he was gonna send to me.

Sure enough, in a few days a box showed up with a bunch of jugs in it.

One of them was a 064 jug that Dennis had ported. He told me that he was falling timber when he built that saw, and during the week it was his work saw, but on the weekends, he used it to race.

The saw had finally suffered a bearing failure, and the squish band was full of metal bits. Dennis dropped the jug in a box and forgot about it for a long while.

We talked again, and he told me to study that jug, and see if I could learn anything from it. So.....I cleaned it up, and gave it a good hard look.



I can tell you what Dennis told me about finger and bridge ports. What he said was very simple. The more transfer you can get around the piston, the power you can make.

I would've like to study the whole saw!

Sure seems like a lot of velocity loss with the lowers ground like that. That's why nothing is set in stone and what works for one saw may not work for the next

 

[Mastermind]

No. They are even. The fingers are about 3° higher than the main transfers though.

I think that by opening the fingers first, the exhaust is forced out ahead of the main transfer charge. That means a purer combustible mixture.....

 

[Barneyrb]

I'm not really all that book smart.....I'm just pretty good at copying what I've seen other people do. So, I can't even begin tell you exactly how this stuff works.

I will gladly tell you how I began using bridge and finger ports.

Dennis Cahoon and I were talking about saw parts that he had piled up one day, and he said he had some jugs he was gonna send to me.

Sure enough, in a few days a box showed up with a bunch of jugs in it.

One of them was a 064 jug that Dennis had ported. He told me that he was falling timber when he built that saw, and during the week it was his work saw, but on the weekends, he used it to race.

The saw had finally suffered a bearing failure, and the squish band was full of metal bits. Dennis dropped the jug in a box and forgot about it for a long while.

We talked again, and he told me to study that jug, and see if I could learn anything from it. So.....I cleaned it up, and gave it a good hard look.



I can tell you what Dennis told me about finger and bridge ports. What he said was very simple. The more transfer you can get around the piston, the power you can make.

Randy, any idea if this saw was running stuffers on the crank?

 

[Mastermind]

This is pretty cool......

We can have a conversation without anyone feeling the need to prove how smart they are.

We are gonna learn how to build some really good saws here.

 

[Mastermind]

Randy, any idea if this saw was running stuffers on the crank?

I don't think so.

The numbers were really high. I've yet to run it either.

 

[Sty57]

So in my small minds eye. Would it be better with a smaller intake port size and a bigger carb to keep the velocity up?

 

[Sty57]

It would be very cool to have some kind of Flow Bench to be able to see the changes.

 

[Deets066]

This is my 066 jug. The only reason it has exhaust side bridges is because I started grinding on that side by accident. I would have never tried this on purpose. But maybe it was a good thing cuz the saw runs well. But I have no explanation why, kinda goes against the velocity theory.

 

[czar800]

It would be very cool to have some kind of Flow Bench to be able to see the changes.

I have a friend that has some kind of software for flow... It's all was way over my head when we talked about it. He said it could be used to make piped saws and such. I'm not the guy for using it or understanding it, but I could maybe get it for someone.

 

[bikemike]

View attachment 9689

This is my 066 jug. The only reason it has exhaust side bridges is because I started grinding on that side by accident. I would have never tried this on purpose. But maybe it was a good thing cuz the saw runs well. But I have no explanation why, kinda goes against the velocity theory.

Yeah it does sing a nice song

 

[czar800]

Ok I just asked him what it was.
Vitual 2 stroke And virtual 4 staoke