Flowmaster sidepipe 13530320 Question

[Pastormajorquin]

Hello!
I need some information about the flowmaster 30 inch sidepipe replacement muffler.
How much quieter are they, than the original backdraft sidepipe?
The problem is, that I need a quieter solution for my roush 402r engine, because otherwise my neighbors probably get angry after a while! Does anybody has some soundfiles of it in comparison to the original setup?
Would be glad to get some information from backdraft drivers!

Thanks

[cycleguy55]

This has been well covered. Search 'Flowmaster Slimline' on CC and you'll find links to videos with sound level measurements, etc.

[TexasSnake]

Maybe you should be looking for information regarding a good realtor. If your Roush 402 with stock Backdraft exhaust upsets your neighbors I don't think you will never find a solution that meets their expectations.

[cycleguy55]

Originally Posted by Pastormajorquin

Hello!
...my neighbors probably get angry after a while!

I don't have a BD, but I've had ZERO problems with my neighbours - other than fingerprints and requests for rides.

OTOH, I don't rev the engine unnecessarily and I drive very sedately around my neighbourhood, both coming and going. BTW, I was on a first name basis with virtually everyone on my cul-de-sac before I bought the Cobra, and I maintain those relationships. I'd much rather have them approach me with a complaint than calling town council or the local law authorities.

[Cobra #3170]

I just added flow masters because my car was so loud the would not allow us to run in the Goodguys autox in Del Mar Ca. They really quieted the car down especially the high frequency portion of the sound spectrum. It probably took out about 100 hp too but that isn't a big problem because my car is so traction limited already. I liked the old sound better but you can't fight city hall.

Bottom line they work

[hotrodyankee]

just installed those mufflers on my car, quieted down a bit and got rid of the high frequency. Still sounds good. As far as taking away horse power, I don't think so.

[Pastormajorquin]

Thanks for the infos! At the moment I don‘t have problems with my neighbors, but if I can avoid any problems I will take care of it. The thing is, you can‘t start the engine in the morning, without waking up the peoples. But if I can get it quieter at idle and don‘t have the high frequencies it would be great to run out of my neighborhood without getting into trouble. Do you have pictures of your cobra with flowmaster installed cobra3170 and hotrodyankee?

Thanks

[Cobra #3170]

Originally Posted by Pastormajorquin

Thanks for the infos! At the moment I don‘t have problems with my neighbors, but if I can avoid any problems I will take care of it. The thing is, you can‘t start the engine in the morning, without waking up the peoples. But if I can get it quieter at idle and don‘t have the high frequencies it would be great to run out of my neighborhood without getting into trouble. Do you have pictures of your cobra with flowmaster installed cobra3170 and hotrodyankee?

Thanks

They can be seen briefly at the end of this video, they are ceramic coated in satin black. I guarantee they lose power over a 21/2" ID glass pack but they also quiet the car down a bunch, too much for my taste but Goodguyd does not want to annoy others so they will stay on.

https://www.youtube.com/watch?v=kebN14i7MAA

[hotrodyankee]

I don't have them on the car at the moment, took them off to have them ceramic coated.

[spdbrake]

I’m traveling this week but will post couple of pics on Friday

[Pastormajorquin]

Perfect!
Thanks spdbrake

[spdbrake]

The Flowmasters flow much better than the stock BDR mufflers having only two 7/8" perforated holes...


They do come unpolished so plan on spend some time sanding and buffing


And they are a bit larger ID than OD of the pipes. I took mine to a muffler shop and had forward pipe and tail spouts expanded a bit. (Don't push it they can crack) You won't get a perfect slip fit but the welds won't be enormous.
Ensure you install the muffler with the short depth cone on the inlet.
https://www.youtube.com/watch?v=Xuww8Yjyzsk


While your at it you may want to change the rubber support mounts. Bosal PN 255-481 $2.00 per most everywhere.


I added a hose clamp around the mount. Just snug enough to keep it in place and reinforce the mount from tearing.






Sound data from a earlier thread
need sidepipe options to get the decibel level down

Last thing: These are 1/2" larger OD than stock and the heat shields won't fit without re-contouring and larger clamps. They run a lot cooler with the Ceramic insulation in the case but my wife still got a pretty good Snake bite getting out of the car...

[Jdata]

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

[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.

[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.