Part One: The Exhaust Port

[redtractor]

Questions

1. What is a Relief Step?
2. When talking about width as % of diameter, say 70% of a 2" bore is 1.4", is that 1.4" along the curve or a straight line?

 

[Lightning Performance]

Questions

1. What is a Relief Step?
2. When talking about width as % of diameter, say 70% of a 2" bore is 1.4", is that 1.4" along the curve or a straight line?

Straight. 70 is a long way to go. Be sure of your port shape and bevels.

 

[Mastermind]

I'll try to find a picture of a stepped floor.

 

[Adirondackstihl]

I'll try to find a picture of a stepped floor.

 

[countryhog]

can't grind this port because you run into a problem called piston ring locator pins
View attachment 68384

So are the ring pins on either side of the center circular port? If so, seems like you could still square them up to gain more discharge area. Beyond my knowledge as to whether that would help or hinder. Be curious to know since i have couple project saws like that that i havent gotten to yet

 

[Mastermind]

View attachment 69112

Thansk.

 

[lumberjackchef]

So are the ring pins on either side of the center circular port? If so, seems like you could still square them up to gain more discharge area. Beyond my knowledge as to whether that would help or hinder. Be curious to know since i have couple project saws like that that i havent gotten to yet

Most of the old magnesium saws that I have been into have similar ports to this and some do not have any locator pins fort the rings...... have you had this one apart to see where they are located or if they are present?

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[PogoInTheWoods]

Was Googling for old Mac stuff and ran across a vid of an old saw builder in B.C. who explained his exhaust port polishing simply as a means to help reduce cylinder heat on the exhaust side. Smoother surface equals less surface area than a porous, bumpy one, (relatively speaking, of course). The rougher finish has a greater surface area simply due to its texture having vertical surface area in addition to horizontal surface area. Rougher gets hotter than polished and retains heat longer as a result. Only reason he polishes.

 

[Chainsaw Jim]

How's this for an exhaust roof?

 

[paragonbuilder]

Was Googling for old Mac stuff and ran across a vid of an old saw builder in B.C. who explained his exhaust port polishing simply as a means to help reduce cylinder heat on the exhaust side. Smoother surface equals less surface area than a porous, bumpy one, (relatively speaking, of course). The rougher finish has a greater surface area simply due to its texture having vertical surface area in addition to horizontal surface area. Rougher gets hotter than polished and retains heat longer as a result. Only reason he polishes.

Anyone ever test this? I've heard this a lot, but is it true? A rougher surface creates a boundary layer as air flows across it, maybe it would actually absorb less heat?


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[paragonbuilder]

How's this for an exhaust roof?

View attachment 71805

At that angle, that looks very flat. What is it Jim?


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[drf256]

How's this for an exhaust roof?

View attachment 71805

If that jug is upside down, it looks pretty nice Jim.

 

[mdavlee]

It's square for sure. Will flow real quuck after opening

 

[Mastermind]

As long as the bevels are good.....

 

[srcarr52]

Anyone ever test this? I've heard this a lot, but is it true? A rougher surface creates a boundary layer as air flows across it, maybe it would actually absorb less heat?


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The rougher surface reduces the boundary layer. This is why a rough surface has better mass flow than a smooth surface but it does increase heat transfer.

 

[paragonbuilder]

The rougher surface reduces the boundary layer. This is why a rough surface has better mass flow than a smooth surface but it does increase heat transfer.

Ok. That makes sense.
So in the case of an exhaust port, which is more important? Is the excess heat absorbed an issue? Or can the jug design handle the heat and the improved air flow a better choice?


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[Motorhead]

How's this for an exhaust roof?

View attachment 71805

Good bevels,Stay around 60 percent,no problem.

 

[Chainsaw Jim]

At that angle, that looks very flat. What is it Jim?


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That is an 034 super exhaust straight from the factory. It hasn't been ground on in any way.

 

[drf256]

Is it upside down Jim?

Either way it's pretty square. Impressive. I wonder what the inner bevel looks like.

 

[Chainsaw Jim]

Is it upside down Jim?

Either way it's pretty square. Impressive. I wonder what the inner bevel looks like.

No it isn't upside down.