Flowmaster sidepipe 13530320 Question

[Tommy]

Originally Posted by cycleguy55

Flowmaster Slimline mufflers are 3.5" ID, and FM claims the combined surface area of the holes in the cones is greater than the cross-sectional area of the ID. I realize there's some restriction in forcing the exhaust through a bunch of little holes, but I fail to understand how they still won't flow at least as much as a 2.5" ID pipe with louvers or holes - especially when the cross-sectional area of a 3.5" circle is nearly double that of a 2.5" circle.

Please explain.

I'm speaking as a long retired aero engineer who studied this stuff a very long time ago, but here's what I think I remember. Here's a picture of a fluid (e.g., air) going through an opening (in this case a pipe).



This illustrates that the fluid nearest the perimeter of the opening is essentially stationary relative to the wall of the opening. The fluid farther from the perimeter moves faster until it reaches the free flow speed far away from the wall. The distance from the wall to the free flow region depends on a variety of factors including the density of the fluid, temperature, smoothness of the opening and turbulence of the fluid as it enters the opening. ... The main thing to note is that the amount of fluid passing through the opening under any given set of conditions increases dramatically as the size of the opening increases. This is because large openings provide a much larger area where the free flow speed is possible. So a single large opening will always flow better than a number of smaller openings with the same or even larger total open area.

[joyridin']

Originally Posted by Tommy

I'm speaking as a long retired aero engineer who studied this stuff a very long time ago, but here's what I think I remember. Here's a picture of a fluid (e.g., air) going through an opening (in this case a pipe).



This illustrates that the fluid nearest the perimeter of the opening is essentially stationary relative to the wall of the opening. The fluid farther from the perimeter moves faster until it reaches the free flow speed far away from the wall. The distance from the wall to the free flow region depends on a variety of factors including the density of the fluid, temperature, smoothness of the opening and turbulence of the fluid as it enters the opening. ... The main thing to note is that the amount of fluid passing through the opening under any given set of conditions increases dramatically as the size of the opening increases. This is because large openings provide a much larger area where the free flow speed is possible. So a single large opening will always flow better than a number of smaller openings with the same or even larger total open area.

I just saw this post from a few months ago. Does this change at all when heat is applied? If your exhaust gasses run at 1000 degrees and the pipe is at say 400 degrees, does it change the flow characteristics? Or, if you heat up the pipe to 900 degrees vs. the 400 degrees, does that change the flow?