Test pipe?
05-06-2004 | 05:40 PM
#16
Race Director
Joined: Jul 2001
Posts: 14,075
Likes: 3
From: Santa Barbara, CA
"The only truly restrictive style of muffler is a chambered one, like the stock rear muffler."
"The most free-flowing style is a straight-through muffler, or a glasspack. "
Well, they may appear to be non-restrictive because you can see through them, but they effectively have a diameter of about 67-75% of their actual cross-section due to the louvering in the glasspack and the outer expansion-chamber in the straight-through design.
It's just about flow-path, but the path's diameter and velocity. As laminar flow goes past the louvres in the glasspack, each one is like a little wing that diverts the air-flow into the center of the stream. This creates little vortices after each louvre, effectively cutting down on the diameter where laminar flow occurs.
On the straight-through muffler, the gas expands into the outer chamber as it enters the muffler. This slows down the air-column and increases its back-pressure. Then as both the gas flow down the central tube and outer chamber in parallel, they have to re-converge at the end. Dumping the slower gas from the outer chamber back down into the center core again slows down the whole column and increases back-pressure even more. So to effectively get the same flow as a 3.0" in straight-pipe, you need a straight-through muffler with at least 4.0" ID.
"The most free-flowing style is a straight-through muffler, or a glasspack. "
Well, they may appear to be non-restrictive because you can see through them, but they effectively have a diameter of about 67-75% of their actual cross-section due to the louvering in the glasspack and the outer expansion-chamber in the straight-through design.
It's just about flow-path, but the path's diameter and velocity. As laminar flow goes past the louvres in the glasspack, each one is like a little wing that diverts the air-flow into the center of the stream. This creates little vortices after each louvre, effectively cutting down on the diameter where laminar flow occurs.
On the straight-through muffler, the gas expands into the outer chamber as it enters the muffler. This slows down the air-column and increases its back-pressure. Then as both the gas flow down the central tube and outer chamber in parallel, they have to re-converge at the end. Dumping the slower gas from the outer chamber back down into the center core again slows down the whole column and increases back-pressure even more. So to effectively get the same flow as a 3.0" in straight-pipe, you need a straight-through muffler with at least 4.0" ID.
