Piped 046 - On A Budget

[Danger Dan]

Picked up an 046 from ebay. It's an old work saw that was described as a runner. Gonna go thru it, clean it it up and stick a pipe on it.

 

[Danger Dan]

Built a pipe for an 046 a few years back. Used the formula that Timberwolf posted to come up with the design. At that time I wanted a versatile saw that could run on a pipe or muffler.
This time, the plan is to go for a more aggressive exhaust port configuration.

First thing is tear the ebay special down, clean it up, see what's missing and what needs to be replaced:

As can be seen in the picture the p&c are slightly scored. It's also missing a clutch spring, one roller from the clutch bearing, the chain catcher, the paw for the chain adjuster and the brake handle

 

[Danger Dan]

The pipe is actually a "Tuned Pipe", tuned to a specific engine that has its own set of parameters that include:

- Displacement
- Exhaust and Transfer durations
- Blowdown
- Exhaust nozzle dimensions
- RPM

These parameters are plugged into a formula that will provide the pipes critical dimensions

 

[Danger Dan]

Here's a diagram of the components of a simple pipe:

- Exhaust port, (Nozzle)
- Head pipe, (Header)
- Diffuser section
- Dwell section, (Belly)
- Convergent section, (Reflector)
- Stinger

The "Tuned Length" of the pipe is from the PISTON FACE to the MIDPOINT of the Reflector, (convergent section).

 

[Danger Dan]

The plan is to use the original pipe, but to modify the tuned length, which is dependent upon the new exhaust duration. This will keep costs on budget.

Present costs:

Stihl 046 = $242
Chain adj paw = $8
Pipe = $140
Total = $390

Had a spare spring and bearing for the clutch.
Also plan on saving p&c

 

[CHEVYTOWN13]

Pipes grass roots style

Here's mine. The total was less than 25 pesos

The little big man aka PS5100S is running a 3/8 8 pin rim:jawdrop:

 

[Danger Dan]

25 pesos? Looks good!


Calculated the dimensions of the components and then sketched them on some cardboard to build a model:

 

[Danger Dan]

Traced the cardboard on to some 20 gauge sheet metal, then cut and rolled the components.
Made the tapered header out of a tailpipe extension.

 

[Danger Dan]

A fellow forum member, (who wishes to remain anonymous and who is a scholar and a gentleman) welded up the components.
As you can see, he does good work:

 

[jnl502]

that is a fine looking pipe welds look real good but did u figure all the #'s from the saw port timming,blowdown,area? did not see any of this info yet so was wondering. what fuel are u going to run? we need more details or at least i would like to know more.
jnl

 

[CHEVYTOWN13]

You did an awesome job of rolling that steel

You got me fired up to do another pipe build. This time for the Husq 365 Special.

 

[CHEVYTOWN13]

So how did it run?

 

[Danger Dan]

that is a fine looking pipe welds look real good but did u figure all the #'s from the saw port timming,blowdown,area? did not see any of this info yet so was wondering. what fuel are u going to run? we need more details or at least i would like to know more.
jnl

Gonna run gas and originally figured the numbers, (using Timberwolf's formula) from:
Exh Dur = 164'
Xfer Dur = 124'
Blow Dn = 20'
Exh Nozzle = 29h x 31w x 25d
RPM = 13000

For this thread gonna increase to:
Exh Dur = 170 - 180'
Blow Dn = 25 - 30'

Here is the current port timing, (with gasket) of the ebay special:
Exh Dur = 156'
Xfer Dur = 106'
Blow Dn = 25'

Will post more info as the thread progresses,
Thanks

 

[Danger Dan]

So how did it run?

Was happy with it for my 1st try at a pipe, but think there's more to be had.
Have a low quality video that I'll post later.

 

[Danger Dan]

Pipe Tuned Length

Tuned length is a function of:
- Speed of sound = 42550 mm/sec, (after TW correction factor)
- Exh duration = 175'
- RPM in the cut = 13000

TW's formula = (42550x175)/13000=572.79mm or 22.55"
In other words, if exh duration is increased at a given RPM the tuned length is also increased.

Present pipe tuned length = 21.13, so the length may have to be increased

NOTE: TW and Jennings define Tuned Length as the distance from the face of the piston to the mid point of the reflector, while some others use the end of the reflector, (where it meets the stinger) to define it.

Also, reflector midpoint should be calculated as if stinger was not present and the reflector had a closed tip.

 

[Stihlverado]

Gonna run gas and originally figured the numbers, (using Timberwolf's formula) from:
Exh Dur = 164'
Xfer Dur = 124'
Blow Dn = 20'
Exh Nozzle = 29h x 31w x 25d
RPM = 13000

For this thread gonna increase to:
Exh Dur = 170 - 180'
Blow Dn = 25 - 30'

Here is the current port timing, (with gasket) of the ebay special:
Exh Dur = 156'
Xfer Dur = 106'
Blow Dn = 25'

Will post more info as the thread progresses,
Thanks

Im still REALLY new to this and only have experience with basic gasket matching type porting, So now my newbee question!
How do I go about figuring out the "blow down". Figuring out the timing and duration are by using a degree wheel per compression stroke, am I correct on this? Dont mean to annoy just interested in learning more. Thanks

 

[Danger Dan]

Im still REALLY new to this and only have experience with basic gasket matching type porting, So now my newbee question!
How do I go about figuring out the "blow down". Figuring out the timing and duration are by using a degree wheel per compression stroke, am I correct on this? Dont mean to annoy just interested in learning more. Thanks

I’m still learning too, but FWIW…
- Timing disc is used to find port timing in degrees with reference to TDC.
- Blowdown is the number of degrees between where the exh port opens and where the transfer ports open.
- Duration is the port open number multiplied by 2 and then subtracted from 360’.

It’s a numbers game, but it is also like playing chess because you need to think ahead. One wrong move up front can limit what you can do later on. I’m running into that right now with the pipe’s Header. The header length is a function of blowdown and transfer duration, so I’ve already limited my options with respect to those numbers. On the plus side though, maybe all this thinking will delay the onset of Alzheimer’s

 

[gink595]

Here is some Cone Layout software, you type in the dimensions and it lays the flat pattern out for you, all you have to do at that point is transfer it to sheetmetal afer printing it out to a 1:1 scale from your computer. Works really slick. Also has a 21 day free trial period

http://www.pulserate.com/index.php?content=download

 

[gink595]

Here is the output that was used on mine.

This lets you make the "segmented" taperd header.

 

[Stihlverado]

Any vids on the Dolmar !?!?