Real talk about saw porting theory (no arguments)

[Mastermind]

Just think how many freeloaders you're paying for this week[emoji45]

Ok. Stop talking about me.

 

[mdavlee]

Ok. Stop talking about me.

Yeah yeah. You work for a living.

 

[Keith Gandy]

I'll be happy to hand it to you running Doc, plus I've actually lowered compression with the new setup.

I'm looking forward to the warmer weather, I've had enough of this cold stuff

Cmon down here to La. And operate this D9! I got the AC on and its 77° outside

 

[mdavlee]

I'm still gonna stick with the 360. Sometimes it's easier to understand things by an example.

So the 360 is a dual port cylinder fed closed transfer loop scavenged 2 stroke engine.

Let's do the combustion sequence.

The piston is at TDC and combustion occurs in milliseconds. The pressure, not an explosion, of combusted gasses exerts force on the piston crown and drives the piston downward.

So the exhaust roof will open first and vent the combustion pressure. The time between this opening and the upper transfer opening is blowdown. It's said that 90% of exhaust pressure (but not volume) is vented in the first 10* of exhaust opening.

At the same time or before the exhaust is opening, the piston skirt is closing or has closed the intake port and is compressing the charge it has already pulled into the case.

Then the roof of the transfers open and there is a sudden flow of charge into the cylinder. As the exhaust is heading towards the front of the motor, the charge is forced towards the rear of the motor which creates a "loop" of gasses.

From reading the bike guys point out flatter transfer roofs are better for wider power and and roofs pointed to the plug is better for top end. Husky 372 have one set of each.

The last 46 I put together is a hodgepodge of parts with a D chamber cylinder with no machine work and creative grinding to match the piston used. In a cant it's the fastest one I've done. I haven't actually took it out and used it as a worksaw with a 28" bar or anything to see how it acts. I think it will work fine since it had great manners tuning and idling. Case volume has been reduced and transfers are stock width and uppers only leveled.

 

[Keith Gandy]

From reading the bike guys point out flatter transfer roofs are better for wider power and and roofs pointed to the plug is better for top end. Husky 372 have one set of each.

The last 46 I put together is a hodgepodge of parts with a D chamber cylinder with no machine work and creative grinding to match the piston used. In a cant it's the fastest one I've done. I haven't actually took it out and used it as a worksaw with a 28" bar or anything to see how it acts. I think it will work fine since it had great manners tuning and idling. Case volume has been reduced and transfers are stock width and uppers only leveled.

Ive tried them both ways on a 2 port and prefer flat for a worksaw

 

[mdavlee]

Ive tried them both ways on a 2 ports and prefer flat for a worksaw

Me too. In quad ports I put the primary flat and secondary angled

 

[Keith Gandy]

Maybe poiting toward the plug has a increase in velocity through the loop and faster blowdown of exhaust? Kinda the way in my mind Im seeing it

 

[mdavlee]

Maybe poiting toward the plug has a increase in velocity through the loop and faster blowdown of exhaust? Kinda the way in my mind Im seeing it

It could.

 

[Keith Gandy]

Im still pondering on progressive opening in a 2 port to simulate a quad port. A bump to help push initial charge on through the loop?

 

[mdavlee]

Im still pondering on progressive opening in a 2 port to simulate a quad port. A bump to help push initial charge on through the loop?

That's an option. Raise both ends and leave the center where it's at.

 

[MustangMike]

Take care of that arm Doc, and thanks so much for the info in the thread.

Had bad tendentious 2 years ago from splitting too much by hand. Had to learn how to start a saw left handed!

Reach the arm out horizontally, open & close your hand, and rotate it as much as possible. (I'm giving advice to a Dr!!!)

 

[Keith Gandy]

That's an option. Raise both ends and leave the center where it's at.

Im thinkin on a small purge to start the loop and drop the pressure in the loop and when the main charge is opened the lower pressure in the loop would help draw it in?

 

[jmssaws]

Almost every quad opens a different way but most have close to the same roof angle and entry.
661 is different from any I've seen and I change all of them to about the opposite of the way they are stock but I maintain roof and entry angles.

Before when I tried to hog out the transfers i like many others would kill the saw but it wasn't from doing to much
It was from not doing enough,
To make everything big and raise the entire port is a ton of work but without question it works or I wouldn't keep doing it.

 

[Keith Gandy]

Almost every quad opens a different way but most have close to the same roof angle and entry.
661 is different from any I've seen and I change all of them to about the opposite of the way they are stock but I maintain roof and entry angles.

Before when I tried to hog out the transfers i like many others would kill the saw but it wasn't from doing to much
It was from not doing enough,
To make everything big and raise the entire port is a ton of work but without question it works or I wouldn't keep doing it.

Not sure what u did on that last 661 video u posted but it worked!!!

 

[paragonbuilder]

Al you should write the first chainsaw porting book! Your style of writing is clear and concise, understandable, and very informative. Thank you for that!!!
[emoji106][emoji106][emoji106][emoji106][emoji106]


Sent from my iPhone using Tapatalk

 

[jmssaws]

I wasn't killing velocity from adding case capacity, I was killing the way they dump into the cylinder.
The way I do a 661 has to add a enormous amount of capacity but it doesn't hurt it
Quite the opposite actually.

I don't know how much velocity there is in a saw but I know to make more power you have to get more fuel on top of the piston and in my mind you can't do that by making things smaller.

 

[jmssaws]

But nothing is definate and there's no set way and what one person does that works may not work for another.

I started porting 20 years ago and have been grinding on saws 10 of that and have changed how I do them many times and I'll change again,the only way for me to keep doing it is to keep looking for something new and there's a million ways to accomplish the same thing,gains are easily has but it's that last little bit that you have to search for.

The only way I know to learn it is to do it,learn how to grind without making a mess and you'll have a easy time with the rest.

 

[Chainganger]

It's great that you are humble my friend. But your work is as good as any I've seen.

Thanks for taking the time to do this excellent write up.

Big rep for you sir.

This should be a sticky!

 

[paragonbuilder]

This should be a sticky!

Fantastic info and right in the beginning! Definitely a sticky!!!


Sent from my iPhone using Tapatalk

 

[MustangMike]

Cmon down here to La. And operate this D9! I got the AC on and its 77° outside

As I'm going around to my appointments, I'm having trouble seeing over the snow banks!!!