NZConvertible

Not necessarily. The rules of fluid dynamics are fairly constant, so no matter what the temperature or pipe material, the relationship between cross-sectional area and pressure drop for a given airflow follows a similar pattern. I looked at different gases in different materials and the results were always about the same.

Even if you just compare cross-sectional area (too simplistic to be accurate), the difference between 3" and 2 x 2.5" is significant. It's pretty obvious that nearly 40% more flow area is going to result in less resistance.
Sorry if that came across as an attitude but it wasn't meant to. It was a genuine challenge to find data better than mine. Short of measuring it yourself I doubt you'll find anything.

The best way to actually prove one system is better than another is quite simple. You just tap a pressure gauge into the system immediately after the turbo or headers and measure exhaust backpressure at full load. The trick is that you need to compare different systems on the same car. Any volunteers?

oregano

iTrader: (1)

To Jason,

I don't think I understand your experiment. You say that in your test, two 2.5" pipes flow better than a single 3" pipe, right?

Ok, I know next to nothing of fluid dynamics so please be patient with me. By flow do you mean volume? If so, you are saying that two 2.5" pipes can flow more volume than a 3" pipe, but not two 2.25" pipes, right?

Hmmmm..... now if that's true, we can find some very interesting numbers. If you calculate the cross sectional area of two 2.5" pipes, two 2.25" pipes, and one 3" pipe, you will see...

area = pi*r^2
area of two 2.5" pipes = 2*(pi*1.25^2)
=9.82"^2
area of two 2.25" pipes = 2*(pi*1.125^2)
=7.95"^2
area of one 3" pipe = pi*1.5^2
= 7.07"^2

Sooo..... as everyone can see, two 2.25" pipes have a LARGER cross sectional area than a single 3" pipe.

But wait, didn't Jason say that a single 3" pipe flows better than two 2.25" pipes?!?!? Sure, maybe two 2.5" pipes flow better than a single 3" pipe, but the have a cross sectional area almost 1.5 TIMES as large as a single 3" pipe! Math doesn't lie does it?

So wut duz this all mean? Well as I understand it (correct me if I'm wrong) a single pipe flows BETTER than a dual pipe with an equal cross sectional area.
Jason said it himself folks!

What is the importance of cross sectional area? Well, I believe (once again, correct me if I'm wrong) this area directly affects the velocity of the exhaust. Less area = higher velocity because the pipe needs to flow the same volume of air through a smaller opening in the same amount of time . Also, higher velocity exhaust uses its momentum to help suck the other dirty exhaust air out of the engine! Thus... increasing HP!!

rrewq

umm... I think the engineering geeks are telling us that there's more to it than just cross sectional area...

NZConvertible

I really didn't want this to turn into yet another physics lesson. This has all been discussed before at some length. But since you asked... It's not actually my experiment, it's published experimental data. But yes, two 2.5" pipes flow better than a single 3" pipe. "Better" means the same flow at lower pressure (less work done by the engine) OR a higher flow rate at the same pressure.
No, I mean flow, as in litres per second or cubic feet per minute.
Correct.
There's your first mistake. As I said above, just comparing cross-sectional area is too simplistic, and doesn't take into account the increase in internal surface area and hence friction losses.
Two 2.5" pipes have ~12% more cross-sectional area than a 3" pipe, but they also have ~67% more internal surface area. It's this additional surface friction that increases flow resistance to more than than of a 3" pipe.

Remember than until now none of my info was calculated. It came from measured experimental results.
You are correct.

Please also remember that this is just the flow through bare pipe, not a complete exhaust system. There are countless other factors that influence how well an exhaust system flows. Obvious ones are muffler design, weld quality (internal penetration specifically), number and radius of bends, quality of the Y in dual systems, etc. The only reason I've posted here is to disprove the blanket statement than "single flows better than dual". It's a stupid thing to say because there are so many other varaibles, and pipe size is probably the most important.

The Unsent

dual exhaust is more sexy. single just looks off to me.

Howi

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howi

oregano

iTrader: (1)

bump