I'm literally modifying my muffler right now and have a question!!!

NebClimber · May 19, 2004

I am at a friends shop and trying to modify my muffler on my 357xp right now.

How do I get the two halves of the muffler apart!!

The two halves are pressed together. How do i seperate them?

And then how do I get them back together?

Steven

ehp · May 19, 2004

I donot take them apart , i just take my porting tool and cut the inner plate with it threw the ext port in the muffler, i just make a hole the size i want to and that is that , then make your hole on the outside of your muffler, make sure you get all the crap back out and the way you go

NebClimber · May 19, 2004

OK. So I'm going to drill a 5/8" hole from the back, then go around to the front and drill another 5/8" hole.

And then clean it out with soap and water.

Sound good?

STEVEN

ehp · May 19, 2004

i put a bigger hole than that in the inside but not everybody has a tool to do that, 5/8's one hole or 2 are you using , 1 hole is not as big as you can go but it should be enough to start with , you will see a difference forsure , because if you get the hole to big the saw will lay down on you in the cut because of not having enough back pressure, and when you drill the hole look for filing hanging on and make sure they are out of the muffler before you start it up

046 · May 20, 2004

To properly size your final port size. The pro's here recogmend 1 to 1.25X your exhaust port size.

Try my spegetti method mod. keep in mind it's way easier to remove more material VS trying to put it back.

Anyways take some small round spegetti and fill up the exhaust port. Then fill up the final exhaust hole/pipe with spegetti. Count the number spegetti from the two ports and divide.

You will get a very close ratio of the two ports.

Use the size the pro's are already using for your particular model and build. don't try to reinvent the wheel. The master builders here have come to the correct size by building a number of muffer mods by trial and error.

For my 335, I emitated a Walkerized muffler, which happened to be 85% of exhaust port size.

I'm a total neophete to muffler mods, but I did come up with a new EZ way to measure ports sizes.

NebClimber · May 20, 2004

To 046: You wrote:

"To properly size your final port size. The pro's here recogmend 1 to 1.25X your exhaust port size.

Anyways take some small round spegetti and fill up the exhaust port. Then fill up the final exhaust hole/pipe with spegetti. Count the number spegetti from the two ports and divide.

You will get a very close ratio of the two ports."

Why would you divide the final number by 2? If the exhaust port off of the cylinder is, say, 10 pieces of spagetti, then shouldn't the hole in the muffler also equal 10 pieces of spagetti (or, if two holes in the muffler, 5 pieces of spagetti each)? This would give you exactly a 1:1 ratio between the exhaust port by the piston and the exhaust holes cut into the muffer.

Please explain what it is that I am missing here.

Steven

rahtreelimbs · May 20, 2004

Wouldn't the easier way be to just measure the exhaust port and do the math?

046 · May 20, 2004

Originally posted by RAHTREELIMBS
Wouldn't the easier way be to just mearsure the exhaust port and do the math?

NebClimber, Sorry I was not more clear.

RAHTREELIMBS, Measure the exhaust port? How? do you have a better way?

Take the 335 muffler as an example.

Let's see, the exhaust port is squarish oval, the internal port needed is oblong and the final exhaust pipe is round.

My method may not be exact, but it sure gets close.

example: number of spegetti in exhaust port = 27 , number of spegetti in final exhaust pipe = 23

23 divided by 27 = .85 or new exhaust size is 85% of exhaust port size.

simple... does anyone have a better way?

bwalker · May 20, 2004

The 1.25x thing is not set in stone by any means. Each saw is differant. I think after a certain point you are just making noise and possibly loseing power so its better to keep it on the conservative side.

046 · May 20, 2004

Bwalker, I totally agree! start conservative.

I copied Walker's muffer size/design, because I figured they know a heck of a lot more about doing these muffler mods than I do.

I don't know what the gain is but, Walkers claim a conservative .5+ hp gain for doing the muffler w/o any porting/polishing.

needless to say I'm really glad I started conservatively with 85% of exhast port size. My 335 now outcuts my 024.

Also take what I post with several grains of salt, as I've only done one muffler mod. (i've ported & polished lots of auto & motorcycle motors)

My contribution is how to accurately measure port sizes by using small round spegetti.

rbtree · May 21, 2004

The 335's that I left the factory port in, and added a 5/8th port definitely outcut the Walker's single port.

Andyshine77 · May 21, 2004

So on a 335 all you need to do is drill a 5/8 hole in the muffler, then add a screen? If so, what size hole would work on a 353 or 372?

rbtree · May 21, 2004

353-two 1/2 inch ports... 372 -two 5/8" or thereabouts.

I have a tube on the 335's and no screen....to get the exhaust past the plastic cover.

Andyshine77 · May 21, 2004

Thanks.

rahtreelimbs · May 21, 2004

I believe that when we are talking about the the size of the exhaust port we are talking about the measurement of the size of the port not the volume. A simple measurement inches is all that is needed. The speghetti method checks volume. I believe that this is right, if not,let me know.

046 · May 21, 2004

Originally posted by RAHTREELIMBS
I believe that when we are talking about the the size of the exhaust port we are talking about the measurement of the size of the port not the volume. A simple measurement inches is all that is needed. The speghetti method checks volume. I believe that this is right, if not,let me know.

Correct, this method checks the volume, which is the size of the ports. If all of the ports in questions were the same shape. Then you could easily measure the size and go on. But unfortunately this is almost never the case.

This EZ method will allow someone to verify the ratio between the exhaust port and final exhaust size, with a fair degree of accuraccy. Different shapes/sizes of ports are handled easily with this method.

046 · Jan 8, 2008

oopssss.... just caught this mistake from long ago.
my spaghetti method of measuring port size, measures size not volume. which would need three dimensions.

still this method is fairly accurate, allowing one to easily measure odd shaped ports.

RAHTREELIMBS] I believe that when we are talking about the the size of the exhaust port we are talking about the measurement of the size of the port not the volume. A simple measurement inches is all that is needed. The speghetti method checks volume. I believe that this is right said:
Correct, this method checks the volume, which is the size of the ports. If all of the ports in questions were the same shape. Then you could easily measure the size and go on. But unfortunately this is almost never the case.

This EZ method will allow someone to verify the ratio between the exhaust port and final exhaust size, with a fair degree of accuraccy. Different shapes/sizes of ports are handled easily with this method.

Danger Dan · Jan 8, 2008

Hole Dimensions:

Diameter = distance across round hole, (one dimension)
Circumference = 3.14 x d or Pi times diameter - distance around outside of hole, (one dimension)
Area = 3.14 x r2 or Pi times radius squared, (two dimensions)
Volume = Area x length, (three dimensions)

The Area is what is being measured. :smoking:

Crofter · Jan 8, 2008

046, I like that method counting spaghetti sticks is a lot easier; then you dont have to learn pie are round and cakes are square (or is it the other way around) to calculate the exact area of different shaped openings.

JackD_ME · Jan 8, 2008

All this talk about cutting drilling chopping holes in mufflers . . . What is the basic carburetor tuning method to keep from leaning it out too much?

Do you need a tach or what?
Basic or advanced, but something on retuning would be cool!

I'm literally modifying my muffler right now and have a question!!!

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