Why round exhaust pipe?

[SuperBuickGuy]

A flat box has more boundary loss than a square box.

I'm getting a chuckle out of this discussion, remember I just put some new front springs in my 55, now I can get under the car without jacking it up first

Yet if you climb under your house, you'll note that the main lines are square, and branch to round... when I asked the question, my initial thought was "dumb" but, I've never seen it discussed; nor do I believe know everything - thus I ask.... and it is a funny question

Have you ever considered that the exhaust pipe is round because that's the easiest way to make pipe?

perhaps, yet with today's manufacturing methods, making square turn is as easy as hydroforming.....

[Beagle]

interesting indeed.. I hadn't ever given it that much thought beyond the diameter.

Price would be my first response - oval tubing is kinda bucks up. I was looking into it for the turbo downpipe on the F250, and got sticker shocked pretty bad. Bad enough to consider yanking the mill and beating the crap out of, errr, clearincing the firewall with a sledge. I found out people were using a portapower with the engine in place.

[squirrel]

Yet if you climb under your house,

around here, houses are all built on concrete slabs.

But yeah...making a big square duct is easier to branch off of. This has nothing to do with exhaust tubing.

[CDMBill]

Boundary losses should be eliminated in a large enough box

There is a point to my question - I need to lose the pipes from under the IRS on the Corvette, but I'm not looking forward to unflattening side exhaust pipes every time I drive this lowered car into a driveway ramp or speed bump (where it goes under the frame) so - mathmatically speaking, pi *r2 = ~ 5 square inches (on 2 1/2 pipe).... which would be neat if 1 1/4 x 5 side exhaust tips would be no net loss in flow..... unless, of course, there's something I'm missing about airflow of round pipe.

There will be some minor loss, but you'd need to run a bunch of Pipemax calculations or other software to figure what is ideal. Better to make it look good and give the ground clearance you want.

[SuperBuickGuy]

around here, houses are all built on concrete slabs.

But yeah...making a big square duct is easier to branch off of. This has nothing to do with exhaust tubing.

I can speak to HVAC because I'm a licensed journeyman (yeah, I have a few classes under my belt) it's square because turbulance is bad in a house-hold system (noise) that's why you have a squirrel cage (snicker, unintended pun intended ) - it moves air without turbulance, and you get great volume. In exhaust (commercial kitchen ductwork) the pipe is square because it's easier to clean out; but it is more labor intensive then round.... but still, I'm not hearing anything which would say "it's a bad idea to go to square and out." Square is really easy to make in 1 plane radii.

[BigBlockMopar]

Here's another one...
With the same wall diameter, a round tube has the same strength and bend resistance in all directions. A square tube only in 4.

[TC]

Well Nascar doesn't have a problem using square exhaust.......

[DanStokes]

My guess is that it really won't hurt performance in any significant way and often Hot Rodding is the Art of the Possible. As I understand gas flow in a pipe, there would be individual vortecees (sp?) in each corner, leading to significant boundary layers. But "a difference isn't a difference unless it makes a difference" (C. Don Paulsell) and I suspect that this wouldn't matter in any practical way.

Dan

[anotheridiot]

around here, houses are all built on concrete slabs.

But yeah...making a big square duct is easier to branch off of. This has nothing to do with exhaust tubing.

square duct also fits between the structure of the building walls to allow the big pipe, otherwise you would have to use 2x10's to get round pipe upstairs.
If you can make a transition I think it would look good. You did mention 1 1/4 x 5 which is well bigger than 2 1/2" round, its closer to 3". There is the back pressure discussion that usually ends up being brought into the discussion that may be a bigger downside of square pipe. I am not about low riding cars, but might steal your idea.

[SuperBuickGuy]

Here's another one...
With the same wall diameter, a round tube has the same strength and bend resistance in all directions. A square tube only in 4.

tell that to my exhaust pipe that got crushed on a driveway entrance

square duct also fits between the structure of the building walls to allow the big pipe, otherwise you would have to use 2x10's to get round pipe upstairs.
If you can make a transition I think it would look good. You did mention 1 1/4 x 5 which is well bigger than 2 1/2" round, its closer to 3". There is the back pressure discussion that usually ends up being brought into the discussion that may be a bigger downside of square pipe. I am not about low riding cars, but might steal your idea.

dumb questions generally turn into the next great idea use away, I'm thinking of using a flowmaster type muffler I built years ago, cutting the back off it, then transitioning to an elbow then the outlet