Nice job Jack!... good info too... I like the new exhaust note!
I've been thinking more about exhaust lately due to the cutout thing. I have been impressed with one new idea by Spartn.... here's my thinking which Jack, Spartn, and I have discussed together.... I believe the ideas are sound (no pun intended, LOL)...
The catbacks available for SHO/MKS/transverse 3.5 EB.... (Except for the new one that Spartn has just gotten completed and Jack has installed) make what I think is at least potentially an error by staying dual and OEM size. I am a fan of dual exhausts, but you can't ignore the math in trying to increase flow after you deal with cats/mufflers/resonators/etc ..which are obvious. see below. Also note the GTR uses a similar design to improve exhaust note without raspiness or drone. I think we often make the mistake of trying to make our V6 sound like a V8... instead of a high performance V6 engine.
The numbers for cross-sectional are usually not thought of with an allowance for pipe wall thickness. All pipe is sold based on it's outside diameter, which is irrelevent to it's flow characteristics. To obtain the correct cross-sectional area of the inside of the pipe, you need to subtract the pipe thickness first. So check it out... using a single 3" pipe is actually bigger in cross section.
Some comparisons of pipe cross sectional area:
OD/ID(")...............Inside Area(sq. in.)
2.5/2.375....................4.430
3.0/2.875....................6.492
3.5/3.375....................8.946
So in fact, a single 3.5" pipe has a larger inside cross sectional area than two 2.5" pipes.
Something else to consider is the inside surface area, as measured along the inside walls, especially for the cooling effects on gas flow. The more wall area, the larger to friction with air trying to move through... This is even more dramatic, especially when the contraction of gas (due to cooling) slows it's movement simply because it looses volume.
Another comparison:
OD/ID...................Inside Surface
2.5/2.375..................7.461
3.0/2.875..................9.032
3.5/3.375.................10.601
As you can see, two 2.5" pipes would have approximately 40% more inside surface area than a single 3.5" pipe. The frictional losses from this extra area would likely be minimal, because the gases along the wall flow very slowly(relative to the gases nearer the center).... but they do move slower due to friction resulting in an increased back-pressure. More important, IMHO, is the cooling effect caused by gases in contact with the wall inside surface area. As these gases cool, they draw heat away from gases nearer to the center. As gas loses heat it loses volume and therefor velocity, the added inside surface of the dual pipes should cool the exhaust more than the single pipe and cause a corresponding loss in velocity of flow of engine exhaust... Cooler weather (which we want for our turb'd engine performance) should actually amplify this effect.
The sound part is proven I think (Thanks Jack!)... dyno's/track times on the MKS/SHO/XSport are still on the way
Just my 2 cents... but I think it's thought provoking when the math is done.
