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  #21 (permalink)  
Old 06-07-2018, 02:09 PM
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[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.
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  #22 (permalink)  
Old 06-07-2018, 04:16 PM
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Default Exhaust volume and velocity

Quote:
Originally Posted by spdbrake View Post
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.
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  #23 (permalink)  
Old 06-09-2018, 11:58 AM
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Hi spdbrake!
Did you lost power by installing the flowmaster?
Do you have pictures of yours?
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  #24 (permalink)  
Old 06-09-2018, 12:04 PM
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I personally think they're great. The butt-dyno seems to agree.
Butt Dyno - $529.95 : KaleCoAuto.com, Your home for the rare, unusual, and hard to find auto parts.

Pics are on post #12 this thread
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  #25 (permalink)  
Old 06-09-2018, 05:19 PM
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Quote:
Originally Posted by cycleguy55 View Post
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.
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Last edited by Tommy; 06-09-2018 at 05:21 PM..
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  #26 (permalink)  
Old 06-11-2018, 08:47 PM
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Quote:
Originally Posted by Cobra #3170 View Post
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
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  #27 (permalink)  
Old 08-10-2018, 09:20 PM
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I just put on the flowmaster sidepipe and the sound is great. It sounds deep and powerful, but also the engine compartment feels a little hotter! My old bdr sidepipe felt a little bit colder in the engine compartment! The hood strut gets so hot, that I can not touch it!
Is it possible that the engine runs hotter with flowmaster pipe! Or is it just because of the higher outside temperature in summer, that makes such a big difference in the engine compartment?
Thanks for info!
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  #28 (permalink)  
Old 08-11-2018, 05:17 AM
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Quote:
Originally Posted by Tommy View Post
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?
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