Dealing With CAT (KAT) Mufflers?

[Sidecarflip]

The issue with a CAT in the muff is the excess heat it generates and that excess heat likes to melt the plastic over shroud.

 

[singinwoodwackr]

Here is an update... I used an old screwdriver and a propane torch to open up the muffler. It was time consuming but not overly difficult. It would have been a much better project on a winter day instead of one with a heat index of 104!

Here are the photos of the innards...

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Here are the modifications:

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I opened the outlet hole behind the spark screen significantly to 3/8". I didn't want to mess with the size/shape of the final outlet as I didn't want to take a chance of melting the plastic muffler guard.

Now... do any of you have any thoughts on how to tune a non-strato 2-stroke that is always under constant/heavy/working load at WOT as is this blower? I can set the "H" to 4-stroke but once you are past that (lean) it is hard to tell where you are at.

You could open the exit hole a bit and weld in a 1/2-3/4” diameter pipe that ends just past that plastic guard.

 

[SteveSr]

After you removed the cat material was there a good increase in performance?

It got rebuilt with a new ring and didn't really run it before removing the CAT.

 

[SteveSr]

You could open the exit hole a bit and weld in a 1/2-3/4” diameter pipe that ends just past that plastic guard.

No access to a welder...

 

[Sidecarflip]

What I find somewhat interesting is..Back in the day when I ran 2 stroke dirt bikes, they all had tuned expansion chambers. A proper expansion chamber is designed to scavenge the exhaust gas at the proper time to allow more fresh mixture to enter the cylinder, hence more power.

I've never seen any stock saw (brand is not important) that comes with a tuned muffler, they are all just tin cans with absolutely no scavenge effect what so ever.

Then they stuff in some kind of catalyist and that makes the tin can even less efficient, not that any of them are efficient in exhaust gas extraction in the first place.