EVO and Eclipse Turbo Parts and Performance

EVO X/RalliArt – Inside the Stock Muffler

We wanted to see what was inside a EVO/RalliArt muffler so we cut one open to see what made it work. As a kid I always got in trouble for opening things to see what made them work.

At low exhaust pressure the flow through the stock muffler follows these red lines. All the exhaust has to flow through _12_ little holes. Then into a chamber where the only escape is a bunch more holes. Then through a 2” pipe into the center chamber, then out through either of the interior tip pipes.


There is a spring loaded flapper door that prevents the exhaust from using the other parts of the muffler.

Once you make enough exhaust pressure somehow this flapper valve opens up. It is a heavy spring, takes maybe about 10-15 lbs pressure to move it.

Once it somewhat blows open, the flow can now follow the yellow lines below. Across into the left side, it can ricochet around a bit and make its way into the center section where it can go out the tip pipes (green lines).

So you can cut an access flap into the top rear of the muffler under the heat shield. We cut three sides of a square and fold the resulting flap up. We cut out this piece of pipe shown in yellow.

So now at all exhaust flow levels the exhaust can flow like in the yellow lines.

Like I said, it is wife and parent proof. You can pay with small unmarked bills so the expense goes unnoticed by the warden. While you might notice the slight sound difference because you knew it happened, no one else will and everything looks stock.

Here is what it looks like when doing the surgery:

Then cutting out the cross pipe:

Then now with the cross pipe cut out:

We then weld the two layers of the muffler cover back up.


Mike W

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