stihl 038av Muff Mod

Hi All,

I have an old 038av that might benefit from a muffler mod.

I searched some, but didn't find my model muffler.
Any advice would be appreciated.


View attachment 90980
View attachment 90979

The area of the exhaust port at the piston is 355 sq mm
The area of the muffler outlet is 121 sq mm (aprox 33% of inlet)

She is just a tad restricted

80% would be 284 sq mm

Looks like a 19 mm ID pipe would do (3/4" ID)

What say you all?

Carl

Need answer

26 have looked, but no answer.

im guessing thats an old enough saw that a muffler mod wouldnt help out that much

hh1341 said:

Hi All,

I have an old 038av that might benefit from a muffler mod.

I searched some, but didn't find my model muffler.
Any advice would be appreciated.


View attachment 90980
View attachment 90979

The area of the exhaust port at the piston is 355 sq mm
The area of the muffler outlet is 121 sq mm (aprox 33% of inlet)

She is just a tad restricted

80% would be 284 sq mm

Looks like a 19 mm ID pipe would do (3/4" ID)

What say you all?

Carl

Click to expand...

See if you can find a triple port 038 M II muffler.

There are ALOT of 038 Super mufflers coming across greedbay. They are 2 port. One port is on the right side, and the other is in the front cover. It is very easy to add the 3rd port on the left side and make a MAG muffler if you cannot find one. You can even put the OEM screen in if you like. I have never had a "straight" 038, so I cannot suggest what to do with that one. It looks like the front cover on yours is solid.

Your math seems off

If you close your original port, then 19mm is right on at 284 square mm ... which gives you the 80% of total port area you calculated.

If you keep your original port. use a tube of around 14 mm i.d. to get the total exhaust area you want. Remember that screens will reduce effective exhaust area by anywhere from 5 to 20 percent (or more if they get sooted). If you keep your openings screened, you might bump up your total area 10% or so.

stap2211 said:

If you close your original port, then 19mm is right on at 284 square mm ... which gives you the 80% of total port area you calculated.

If you keep your original port. use a tube of around 14 mm i.d. to get the total exhaust area you want. Remember that screens will reduce effective exhaust area by anywhere from 5 to 20 percent (or more if they get sooted). If you keep your openings screened, you might bump up your total area 10% or so.

Click to expand...

Yes......

I was going to close the original port, actually mount the new tube where the original slots are.

Think I will just remove the screen.

Thanks for these replies

Carl

move a thread

Can you move a thread to another thread.
You know, incorporate one into another.?

I see now, this one should have been in............

http://www.arboristsite.com/showthread.php?t=36541

Carl

An Idea

I think I will fit a larger tube and slip a bushing/tube with 19mm id inside it.

This way I can try adjusting the length for better results and can also try the oversize outer tube and see how that works.

Carl

Pix

Photos to come!

Photos

This was tig welded

hh1341 said:

This was tig welded

Click to expand...

nice welding. How did you measure the areas?

Measurements

harrygrey382 said:

nice welding. How did you measure the areas?

Click to expand...

Thanks,

The exhaust port is a somewhat tapered front to back so I had to take the measurement in at the piston end, however it is rectangular, so I used inside callipers.

Hight X width = area........... 25.4mm X 13.97mm = 355sq mm

To find the 80% of that area divide by 5 and multiply the answer by 4....equals 284sq mm

To find the pipe ID......divide 284 by 3.14.....then find the square root of the result. this resultant answer is the inside radius of the pipe needed.
Double that answer to get inside diameter of the pipe needed.

284/3.14 = 90.4
Sqrt of 90.4 = 9.5
2 X 9.5 = 19mm...........convert to inches if you like (approx .75")
This is simply the reverse of finding the area of a circle.... Pi X radius squared.

This is based on closing the original outlet ports on the muffler.

Carl

Up and running

Here she is up and running, with the 19mm insert installed.

With the insert removed she is 22.22mm (7/8")

I'll have to do some trials to see which is better.

A definite improvement

View attachment 91148

Carl

hh1341 said:

This was tig welded

Click to expand...

In the first photo of the inside of the front cover...

Nice welds. Just wondering why you have so much pipe inside the muffler?

Ss

BTW

The insert is stainless.



Carl

hh1341 said:

it is rectangular, so I used inside callipers.

Click to expand...

Ah, this is what I was wondering - so you think that was accurite enough?

K9-Handler said:

In the first photo of the inside of the front cover...

Nice welds. Just wondering why you have so much pipe inside the muffler?

Click to expand...

Gives more support and allows me to slide a longer insert in and out "a la" a trombone.

It's my feeble attempt to find a tuned length.

If none of that works out, I'll cut it off.

Just playin' around, is all.

Carl

harrygrey382 said:

Ah, this is what I was wondering - so you think that was accurite enough?

Click to expand...

Sure, this is all ballpark, anyway.

There seems to be quite a bit of leeway.

I like this insert idea, it lets you go from large to small without re-work.
Start large, use inserts, test, when you like it.... make the rest that size. It's sort of a test bed.

Welding this thin stuff is a pain.
Make sure you get it good and clean before welding or brazing.
The process doesn't like carbon or paint.

Carl

hh1341 said:

Sure, this is all ballpark, anyway.

There seems to be quite a bit of leeway.

I like this insert idea, it lets you go from large to small without re-work.
Start large, use inserts, test, when you like it.... make the rest that size. It's sort of a test bed.

Welding this thin stuff is a pain.
Make sure you get it good and clean before welding or brazing.
The process doesn't like carbon or paint.

Carl

Click to expand...

Yeah, doesn't sound bad. I should be a bit more patient! I'm going to mod an 038FB muffler to get the best out of a mag jug - so that'll be quite a bit of opening.
Hope my welding is up to it, should be I think. Going to use a mig, so will make sure everything is nice and clean.