Fingers and Bridge ports

[Sty57]

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.

I think it would be a great tool to see changes and bottle necks in the whole saw.

 

[ft. churchill]

On bridge and finger ports such as some of these pictures, is it always necessary to reverse the piston to move the ring end gap locating pins away from the finger ports? My 064 could use even more zing.

 

[Moparmyway]

But I have no explanation why, kinda goes against the velocity theory.

I "see" what you did there ......
You gained velocity.

 

[jmssaws]

I open fingers 2 degrees before the mains but on my 066 the mains are 120 and the fingers are 116 and it works well.

I'm gonna fill the mains some and see what happens.

 

[jacob j.]

I've had better luck with finger ports on the smaller saws like the 026/260 and 024 Super. I tried a set in an 064 and had decent luck but I think opened up the lowers too much and the motor got a little lazy.

 

[jmssaws]

these gigantic fingers are in the best running cylinder I've done.

 

[Four Paws]

I personally like open transfer saws - when they are done right, they all seem to make real good torque and decent rpm.

jmssaws - your fingers in that jug are basically an open transfer port. Are you running the OEM piston backward, or did you swap in a Husky single ring piston?

 

[Mastermind]

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?

Velocity is key to building torque, but for higher rpm and pure HP, I think volume trumps velocity.

I quit school in the 8th grade.......but I got a GED and started trade school at 16 years old. Learning was really easy when I was younger.......things just stuck in my mind easier. It was during those years that I really dug into engine design. As second year students, we got to hang out at a shop that built Nascar engines. It was then that I learned that HP gains can be had just by spinning the engine faster. BUT.......those high revving engines are turds off the line.

What I'm getting at is this. There is no "right" answer.

It depends on what you want as a "driver".

On bridge and finger ports such as some of these pictures, is it always necessary to reverse the piston to move the ring end gap locating pins away from the finger ports? My 064 could use even more zing.

Depends on the saw.......many times you can use a Husky single ring piston.....

 

[Sty57]

That is what I was getting at.
I would think with a bigger carb and a smaller port size on the intake side, when the finger just cracks open it would really pull hard on the carb.
I would thing you could get better throttle response that way, than with a big intake and big carb.
I'm just spitballing here and maybe way off base......I don't know.

 

[jmssaws]

I'm like you randy only I made it to 10th grade before I had to go to work. I did get a ged not long ago.

That cylinder has a backwards oem piston, exhaust is 100 but still has 230lb of compression.

 

[czar800]

I'm like you randy only I made it to 10th grade before I had to go to work. I did get a ged not long ago.

That cylinder has a backwards oem piston, exhaust is 100 but still has 230lb of compression.

How did you maintain 230lbs? What's the squish at?

 

[jmssaws]

How did you maintain 230lbs? What's the squish at?

Piston is maxed, squish is 026.

 

[czar800]

Piston is maxed, squish is 026.

What do you mean by maxed? I'm a little behind....

 

[Sty57]

That is what I was getting at.
I would think with a bigger carb and a smaller port size on the intake side, when the finger just cracks open it would really pull hard on the carb.
I would thing you could get better throttle response that way, than with a big intake and big carb.
I'm just spitballing here and maybe way off base......I don't know.

The thing that got me thing of this is that 024/026 you built. Wasn't pulling the choke shut on it, I would think maybe a bigger carb on it wouldn't pull on it as hard.
There has to be a bottleneck some place on any motor and thats what everyone is chasing.

 

[Mag Craft]

Finger Ports work on open port transfers as well as closed port. I think I saw a picture one time of a saw that Mastermind had put finger ports into a open port transfer cylinder. That saw ran pretty strong if I remember correctly.

 

[junkman]

One of my saws has fingers ,it needs to be tuned higher in rpm than a reg jug does to run right .

 

[Mag Craft]

That is what I was getting at.
I would think with a bigger carb and a smaller port size on the intake side, when the finger just cracks open it would really pull hard on the carb.
I would thing you could get better throttle response that way, than with a big intake and big carb.
I'm just spitballing here and maybe way off base......I don't know.

You mean like a venturi effect.

 

[jmssaws]

What do you mean by maxed? I'm a little behind....

It's almost free ported on the exhaust, I cut the chamber until I'm out of piston skirt then raise the exhaust to get rpm and keep all the compression I can.

Daves short bar saw is gonna be the same only I'm going back to 98 on the exhaust but with all the compression I can get.

 

[Sty57]

You mean like a venturi effect.

Yes that's what I'm thinking.
The way I see it you have to keep following the bottleneck in or out.
If the it's pulling really hard on the carb side, what is the next thing inline. Bigger carb then the air filter.

 

[Sty57]

I will admit that I have No working knowledge of any of this stuff, I'm just a silly farm kid that likes to take stuff apart.