Why round exhaust pipe?

[SuperBuickGuy]

Thats what I cant understand. HVAC are closed systems. Expansion of the "exhaust" happens in the condenser not to atmosphere. I've been in 71 mph winds, and never felt that coming out of an exhaust pipe.

even the ones you're thinking about aren't closed - they have balance vents to allow for thermal expansion. There's another kind that I suspect you didn't consider - commercial ventilation systems, and they suck all sorts of air or air/liquid products out of spaces... funny aside, or a cooks baseball cap up 40 feet of duct.

I am wondering now what the relative static pressures are - easy enough to measure.... have to take 5 minutes tonight to measure it on the Vette (or whatever is closest and easiest.... actually, that would probably be the diesel) - that will answer your question Randal

[SuperBuickGuy]

Am I missing it, or what's missing from the math is port and tube size will play greatly in exhaust velocity. 71.63mph into what kind of open volume? Like a venturi, you choke down the volume and the speed could increase, unless the restriction is great enough that it back's up and chokes at less than the calculated 71.63mph and pressure builds. You're right though, there is a crap ton more math than you are showing as you are just using average piston speed rather than absolute along with only the time the exhaust valve is open (like Bob is talking about but with cam timing now a factor). Way different than a fixed speed/pressure HVAC system, and of course as mentioned, that is just one cylinder.

whether or not you squeeze 4x4 (bore x stroke) through a 4" hole or a 1.73" hole doesn't matter - it's the same volume no matter what, it's simply the pressure that increases but goes back to whatever the pipe will handle once it is past the obstruction (I realize I'm not being precise, but don't think it's necessary for this concept).

[TheSilverBuick]

even the ones you're thinking about aren't closed - they have balance vents to allow for thermal expansion. There's another kind that I suspect you didn't consider - commercial ventilation systems, and they suck all sorts of air or air/liquid products out of spaces... funny aside, or a cooks baseball cap up 40 feet of duct.

I am wondering now what the relative static pressures are - easy enough to measure.... have to take 5 minutes tonight to measure it on the Vette (or whatever is closest and easiest.... actually, that would probably be the diesel) - that will answer your question Randal

If it's static, change the size of your measuring tube, aka resolution.

[Bob Holmes]

Also when using the fancy rolled in exhaust tips at the tail pipe we seen about 4 HP reduction
just from the rolled tips.... they look nicer(my opinion) but lower HP.... I'm retired now but
this testing was a couple of years ago in the exhaust lab at Chrysler(30+ years in that lab as
well as fuel)

WELCOME!!!!

I hope we see a great deal of participation from you.

[MR P-BODY]

WELCOME!!!!

I hope we see a great deal of participation from you.

Thanks.... I'll be around but I dont like getting into the pissin
matches that occurs on many boards

[JeffMcKC]

Then just say you want the closest amount of back pressure to zero as possible....... Also I was under the impression that when using headers that a vacuum was being pulled in the header tube assisting in drawing the new intake charge into the cylinder during overlap, but how can this happen if there is back pressure in the header tube like you are saying??......... Vacuum, Pressure, you can't have both, or can you??...........

There is no such thing as vacuum, as the air goes out one tube it can lower the pressure in another tube, think pan evac on headers. This is why guy that buy firing order swaps without fixing their headers dont gain much just like those mag swaps you love, just swapping without optimizing does not get you far and makes everyone look good. Just like the carb swap one they are talking about right now.

[Bob Holmes]

Thanks.... I'll be around but I dont like getting into the pissin
matches that occurs on many boards

I certainly understand.

I don't spend my time arguing with folks. I don't find it fun. I know what I know, I know what I don't and I find that trying to help folks that don't want it is a waste of my time.

I hope we have the opportunity to learn something from 30 years of experience at that level.

[mike343sharpstick]

In the early 2000's the factory Honda 600 super stock race bikes had 4 into 1 exhaust systems with a square collector. After the collector it transitioned back to round tube. That obviously worked better at some point in the power band, Honda factory race hardware is serious stuff. The theory was that it reduced turbulence when the pulses came out of the individual tubes into the collector.
That said, it was a short lived design.

[SuperBuickGuy]

In the early 2000's the factory Honda 600 super stock race bikes had 4 into 1 exhaust systems with a square collector. After the collector it transitioned back to round tube. That obviously worked better at some point in the power band, Honda factory race hardware is serious stuff. The theory was that it reduced turbulence when the pulses came out of the individual tubes into the collector.
That said, it was a short lived design.

exhaust surge tank? lol hopefully it was shaped like a pipe bomb

and Randal, sorry, was too busy doing other stuff to actually get to checking flows.... tomorrow night, maybe.

[dieselgeek]

Thanks.... I'll be around but I dont like getting into the pissin
matches that occurs on many boards

More!! please share! OEM-level testing is as good as it gets!