Part Three: The Transfer Ports

[Terry Syd]

Chapter 3 of Blair's book on the design of two-strokes has a fairly comprehensive discussion on 'scavenging' - http://dragonfly75.com/motorbike/2StrokeDesign.pdf

When you go through his work, the engine called 'loop saw' is an old Stihl chainsaw engine.

 

[Adirondackstihl]

A tuned pipe works in both directions. It pulses. At one point it pulls on the exhaust port......and then it reverses to cram the unburned gasses it just sucked out right back in.

 

[Adirondackstihl]

 

[Adirondackstihl]

 

[Adirondackstihl]

 

[Adirondackstihl]

 

[Hedgerow]

View attachment 68733

Proof positive..

Husky's have moar ballz.

Right there...

 

[RIDE-RED 350r]

Well Jim, I stand corrected.

 

[spencerpaving]

View attachment 68730 View attachment 68731

Sooo...that's how they work?

 

[mdavlee]

Sooo...that's how they work?

It's magic

 

[Canadian farm boy]

It's magic

PFM!!!

 

[huskihl]

PFM!!!

Pure?

 

[Canadian farm boy]

Pure?

You got it.
Now that we know what the first and last letters stand for in PFM. I hope everyone can figure out what the middle letter stands for.

 

[Canadian farm boy]

IMO it's hard to just look at any one thing when talking about porting a saw. Everything has to work together. It's a balancing act. To much of one thing or not enough of another and you will be disappointed. I believe that the transfers really are where 50% of the magic comes from.
I have a hard time explaining what I look for when I'm digging around in a transfer port. I want the flow and direction to be optimal without losing velocity. Every transfer port in every cylinder is different no matter the manufacturer or brand.
It's what can make or break you when porting.
On average I bet I spend 4-5 hrs just grinding on a cylinder and over half that time is just in the transfers. It's easy to take out material but once it's gone it's a lot harder to put back.

Again this is just my $.02

 

[CJ Brown]

You got it.
Now that we know what the first and last letters stand for in PFM. I hope everyone can figure out what the middle letter stands for.

F = farmboy?

 

[Deets066]

IMO it's hard to just look at any one thing when talking about porting a saw. Everything has to work together. It's a balancing act. To much of one thing or not enough of another and you will be disappointed. I believe that the transfers really are where 50% of the magic comes from.
I have a hard time explaining what I look for when I'm digging around in a transfer port. I want the flow and direction to be optimal without losing velocity. Every transfer port in every cylinder is different no matter the manufacturer or brand.
It's what can make or break you when porting.
On average I bet I spend 4-5 hrs just grinding on a cylinder and over half that time is just in the transfers. It's easy to take out material but once it's gone it's a lot harder to put back.

Again this is just my $.02

Agreed

 

[Deets066]

There are so many more variations on transfers than any other aspect of porting, to me anyway. It seems as they are where a better part of the power is made.

I believe the main reason my hybrid is a good runner is because of the way the trans were shaped and timed stock. They were perfect, when you find that certain cylinder that you just know it is gunna snort.... don't mess it up cuz they are hard to come by.

 

[drf256]

I just grind the fùcking things. If they don't run good, I grind some more.

You guys think too much.

 

[huskihl]

I just grind the fùcking things. If they don't run good, I grind some more.

You guys think too much.

^ word

 

[Deets066]

I just grind the fùcking things. If they don't run good, I grind some more.

You guys think too much.