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Old 11-20-2012, 07:31 AM   #1
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Another "Flow" Thread

OK All of you that weighed in and educated many of us on how air moves, what say you about the Dream 2? It looks like it would make some difference, yet if it is so dynamic an improvement why does Porsche leave such a large piece of low hanging fruit on the tree?

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Old 11-20-2012, 11:16 AM   #2
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Thirty looks and not a word? Hey I showered today! You do know replying is free for this afternoon as well.
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Old 11-20-2012, 11:27 AM   #3
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I liked it so much I looked twice. Just not sure of the price.

Thanks for showering BTW.
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Old 11-20-2012, 11:39 AM   #4
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OK, I'll bite. Absent any reliable Dyno data, I would say it does exactly nothing. The fact that it's after the mufflers will eliminate any pressure wave scavanging affect.
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Old 11-20-2012, 12:01 PM   #5
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The headers, cats, and the mufflers ARE the low hanging fruit. The piping change of the Dream products look nice but is a 2nd order (very minor) improvement at best. If you have already addressed everything else, then I'd think about this.
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Old 11-20-2012, 12:27 PM   #6
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This the DIY version.
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Old 11-20-2012, 01:17 PM   #7
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I don't want to change mine from stock, I was just intrigued by it and wanted to see what you guys thought. I've seen a similar piece designed for the GT3 advertised in Excellence. I'm sure the double outlet breathes fine.
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Old 11-20-2012, 01:29 PM   #8
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Reminds me of the intake "T" discussion......
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Old 11-20-2012, 02:23 PM   #9
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The same principles hold true in the exhaust as in the intake "T". If the flow is forced to separate from the walls of a tube due to an abrupt change in direction, it will "separate" from the walls and effectively reduce the diameter of the tube. Smooth, gradual transitions are what's needed to keep pressure drop to a minimum.

I'll refer you back to post #16 in the "T" thread:


One aspect that many people don't realize is that the air at the inside of a bend is moving faster than the air on the outside, this is the opposite of the wheels on a car, so it's not intuitive to most folks. Due to momentum, the faster moving flow is more likely to want to keep moving in a straight line so the inside of the bend in a tube is critical to keeping separation from occurring. It's significantly more important to make the inner diameter of a bend large and smooth than the outer diameter.

The exhaust pipes in the pictures will definitely help to reduce backpressure through the exhaust mostly because they make the flow turns more gradual. To what degree depends on the pressure drop in the rest of the system. Considering this is post-muffler, where the air is pretty well cooled off and very turbulent anyway, there's probably not much to be gained.

In addition, they will make a significant difference in the pulsing of the flow between the left and right sides. I suspect the stock system uses the left and right sides to cancel some noise, the designs shown won't be doing as much of that, so they will make the exhaust louder, even without changing the muffler.

Last edited by blue2000s; 11-20-2012 at 02:26 PM.
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Old 11-20-2012, 03:27 PM   #10
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Low hanging fruit

I wonder if the exhaust was "low hanging fruit" to the marketing guys at Porsche who needed to take some power out of the Boxster so that it would compete less against the 911
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Old 11-20-2012, 03:37 PM   #11
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IDK Jfro, the Spyder is right there on the posted online numbers in acceleration and 1/4 mile times with a 911 S in 2011, (in fact zero to sixty.com has it a tad quicker) sure the top end on the 911 is much higher but unless you live in Germany what's the point? They make a piece for the GT3 911 as well so it's not about what model eats the other in this case.

Last edited by Ghostrider 310; 11-20-2012 at 03:40 PM.
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