Flowmaster sidepipe 13530320 Question

[Cobra #3170]

Originally Posted by Jdata

They added power based on a FFR post. This was done via engine dyno, 18 hp. Over glasspacks

The more power you make the more you lose both from a % standpoint and an exhaust volume standpoint. If you are making 400 to 500 they might help a bit depending on cam timing. Over 700 I guarantee a loss just because of the restriction vs a 2 1/2" straight through design.

[cycleguy55]

Originally Posted by Cobra #3170

The more power you make the more you lose both from a % standpoint and an exhaust volume standpoint. If you are making 400 to 500 they might help a bit depending on cam timing. Over 700 I guarantee a loss just because of the restriction vs a 2 1/2" straight through design.

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.

[Cobra #3170]

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.

All I can tell you is that we use a higher average percentage of throttle with the flow masters than we did with the steel packed 2 1/2 inch ID pipes. I suspect that flow may be disrupted more by the multiple holes not parallel to direction of flow despite the greater surface area. We have logs from every run with the new EFI and can see average throttle opening is greater with flow masters.
I guess the only way to really test this would be on a chassis dyno but the data and pure "seat of the pants" says we are down on power. This car can blow a pylon down with the 2.5" ID steel packs it can't with the Flowmasters
so I am guessing exhaust volume/velocity is reduced which will kill power .

[Winchester67]

Personally, I love the "Pylon Test".

[cycleguy55]

Originally Posted by Cobra #3170

I guess the only way to really test this would be on a chassis dyno but the data and pure "seat of the pants" says we are down on power. This car can blow a pylon down with the 2.5" ID steel packs it can't with the Flowmasters so I am guessing exhaust volume/velocity is reduced which will kill power .

Makes sense.

[spdbrake]

[quote= This car can blow a pylon down with the 2.5" ID steel packs it can't with the Flowmasters
so I am guessing exhaust volume/velocity is reduced which will kill power .[/QUOTE]

All thing being equal same rpm etc... the higher velocity pipe will be a choke point. Same as putting your thumb over a water hose end.
Empty a balloon into a drinking straw and it will blow out a candle. Empty the same ballon into a paper towel tube and it usually won't blow it out.
The balloon in the paper towel tube will deflate faster as well.

[Cobra #3170]

Originally Posted by spdbrake

All thing being equal same rpm etc... the higher velocity pipe will be a choke point. Same as putting your thumb over a water hose end.
Empty a balloon into a drinking straw and it will blow out a candle. Empty the same ballon into a paper towel tube and it usually won't blow it out.
The balloon in the paper towel tube will deflate faster as well.

All things are not equal, higher back pressure will yield lower volume and less velocity from the outlet of the 3.5" pipe. The velocity might be higher at one of the small holes at the muffler proper but by the time ii travels through the large pipe diffuses and makes a 90 D turn it has both lower volume and lower velocity because it has already expanded. The VE of the engine is negatively effected by the back pressure created by the Flowmaster. We have not blown over one pylon since installing these mufflers we usually got at least one every two events with the straight through design.

[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?

[Jdata]

Originally Posted by Cobra #3170

The more power you make the more you lose both from a % standpoint and an exhaust volume standpoint. If you are making 400 to 500 they might help a bit depending on cam timing. Over 700 I guarantee a loss just because of the restriction vs a 2 1/2" straight through design.

I agree but the loss will be less compared to the glasspack