Pipe building theory.

[Chainsaw Jim]

I guess I actually do have a before and after without any other modding in between. Though it was already ported for the pipe when running the 064 muffler.
With muffler:

With pipe:

After getting all dialed in with a modified carb and ignition timing adjustment...but no race chain or racing fuel yet:

 

[Fruecrue]

Bump

 

[Fruecrue]

 

[Dub11]

View attachment 114482

What saw is that for?

 

[mgr1]

Howe did you calculate the stinger diameter? If you go less in diameter there will be more heat in the engine.

 

[Fruecrue]

What saw is that for?

How did I know you would show up....

 

[Fruecrue]

Howe did you calculate the stinger diameter? If you go less in diameter there will be more heat in the engine.

From the two stroke tuners handbook.
It’s a formula based on lead in pipe diameter.
lead In pipe diameter times chosen your multiplier.

 

[Fruecrue]

I did make one mathematical error,
Diameter 2 should be 3.125”.
This will also change my cone lengths.

 

[spencerpaving]

I have good luck using a tapered header design vs a straight one....Looking forward to your build

 

[Fruecrue]

I have good luck using a tapered header design vs a straight one....Looking forward to your build

This will be my first build, and I’m not at all sure that I’m interpreting all that I have read correctly. I chose a larger diameter than I believe I needed, hoping for a more forgiving design, and in the interest of simplification.

 

[mgr1]

I have good luck using a tapered header design vs a straight one....Looking forward to your build

How much taper? 2 or 3 degrees?

 

[spencerpaving]

2or 3 depending on the pipe....one thing to remember most pipesaws don't turn the rpm people think they do...The larger dia will help ya...To a certain point

 

[Fruecrue]

This is where I’m at now.
I should mention, my building materials aren’t exactly conventional.

 

[spencerpaving]

Hhmm....Gonna look sweet polished up....I wonder if the copper would effect the sound waves being a heat sink....Couple sled makers in the 70s tried aluminum pipes on the racers....They kept cracking and apparently had to build them very short cause they wouldn't retain heat

 

[Fruecrue]

Hhmm....Gonna look sweet polished up....I wonder if the copper would effect the sound waves being a heat sink....Couple sled makers in the 70s tried aluminum pipes on the racers....They kept cracking and apparently had to build them very short cause they wouldn't retain heat

Interesting. Hopefully will learn if nothing else.
The materials cost me nothing, so I have nothing to lose.

 

[Fruecrue]

@spencerpaving
How much blowdown do you like?

 

[spencerpaving]

Depends...Blonde or brunette...32-35* work good...I have gone as high as 38*..But I would keep it lower...More user friendly

 

[spencerpaving]

Being that yer working on a 390 I would shoot for 30* and see what your compression is...

 

[spencerpaving]

Also with the right pipe a work ported saw with only 20* blowdown can run good too

 

[Fruecrue]

Right now I’m at 178* exhaust duration.
Factory transfers untouched at 125*
34* blowdown.
Compression reads 130 psi.