H-PIPE EXHAUST OR X-PIPE ??

[patmckinneyracing]

It being a terrible metaphor is your opinion. It's basic science using variables such as velocity, distance traveled, etc. The same theories used in relation to sound waves can be used to describe the features of exhaust pulses. The figure 8 racing was a good metaphor to describe exhaust pulses meeting at a central point.

If your going to criticize my explanation of exhaust pulses and the science behind it, I would expect you to be a little constructive and offer up your explanation of how it works rather than saying its wrong or it being a terrible metaphor. I didn't say anything about the results of the two and which was better or there being a huge difference in power, just offering a scientific explanation to give a broader idea rather than just looking at the results.

I don't think, I know.

Use what you want, its your car. Its up to you to decipher all these posts into what you want for your setup. I went with an H-pipe because of cost and was more concerned with equalizing the pressure in both pipes. Didn't care about there being any gains in the torque or hp.

 

[jrm81bu]

I have to agree with the figure eight racing not being a good metaphor. The idea for both the x and h pipe is that each exhasut pulse would be staggered from one side to the other. Meaning they would never "crash into each other". Then when one side passes the opening, either in the x or the h, it would "pull" the on the gasses in the other pipe. This is called scavenging. It's the smae principle that makes an evac set-up work, only instead of it pulling a vacuum on your breather tanks it pulls it on the other bank of the engine.
There is also headers out there that have primary tubes from both banks of an engine going into one collector. Say 3 tubes from the driver side and 1 from the passenger side going into the driver collector, same but opposite for the passenger side. I think they may be referred to as 180* headers, although I might be thinking of something else. I think this is done because of having 2 cylinders on the same bank firing one after the other instead of every firing cylinder being on opposite banks. So instead of scavenging from the opposite pipe, both pipes have the same time between pulses in the pipe.

 

[84sbcregal23deg]

I have to agree with the figure eight racing not being a good metaphor. The idea for both the x and h pipe is that each exhasut pulse would be staggered from one side to the other. Meaning they would never "crash into each other". Then when one side passes the opening, either in the x or the h, it would "pull" the on the gasses in the other pipe. This is called scavenging. It's the smae principle that makes an evac set-up work, only instead of it pulling a vacuum on your breather tanks it pulls it on the other bank of the engine.
There is also headers out there that have primary tubes from both banks of an engine going into one collector. Say 3 tubes from the driver side and 1 from the passenger side going into the driver collector, same but opposite for the passenger side. I think they may be referred to as 180* headers, although I might be thinking of something else. I think this is done because of having 2 cylinders on the same bank firing one after the other instead of every firing cylinder being on opposite banks. So instead of scavenging from the opposite pipe, both pipes have the same time between pulses in the pipe.

yea those are neat!! i always wanted to know how much a set of those 180 degree setups would cost to build. gotta be big $$$!
although i guess if you have a mid-engined supercar, you probably wouldn't care too much lol.

 

[oldtinsmith]

Man!.................I spent at least 4 hours looking through 8 of my 20 or so auto books looking for data on the 'H' vs. "X" pipe debate and searching the web (forums)! A few sites used formulas by David Vizard (pipe sizing, engine CFM per engine horsepower, etc.). I have 3 books by David Vizard and learned a few things [ David Vizard: Engineer, Race car driver & builder, Inventor, and does independent research on engine building ] such as, balance tube ("H" pipe), crossover pipes ( "H", "X", & "Y" pipes), over/under "X" pipe, pressure wave terminator boxes (types), gang muffler systems, etc.!
I won't get into debating the "H" vs. "X" pipes because to me it would be like debating political parties or religion!!! :lol: What I will tell you is how I plan on doing my exhaust system when the time comes (my El Camino will be street diven only!).
I will be buying a BRAND NAME 4 into one header.
I will be using a balance tube of 1 7/8" minimum dia., and installing it as close to the collector as possible (or mounted into termination boxes, witch will be a minimum of volume of 8 times the volume of one cylinder).
I will be using an "X" pipe behind the transmission, or use gang mufflers.
I won't have a engine of more than 400 horsepower, so I'll be using 2 1/2 exhaust pipe and 2 1/4 tail pipe (exit behind the wheels).
This should really get the nay sayers roaring!

Doug

 

[78PontiacGP]

Gases in the pipes would deftinally flow better with an x-pipe than an h-pipe.

 

[oldtinsmith]

Check this out from Third Gen. Org!

Crossovers

Crossovers are most effective for V8 engines. This is because of a V8's unbalanced exhaust pulse timing. Here's a simple picture, of a Chevy V8 turning 6 revolutions.

...Left bank: |..|.||.|..|.||.|..|.||.
Firing order: 184365721843657218436572
..Right bank: .||.|..|.||.|..|.||.|..|

The vertical bars indicate when a bank has a firing cylinder. This very clearly shows that as the engine runs, the left manifold (or collector) sees two exhaust pulses in rapid succession when cylinders 5 and 7 fire. Same for the right when 8 and 4 fire. So when 5/7 fire, the left side has an extra-wide pressure wave and the right side has a low pressure area. When 8/4 fire, the left side has the low pressure area and the right side gets the extra-wide pulse. This tends to mess up the tuning for those cylinders.

FOR A V8--
It is not possible to adjust the firing order to prevent this in a V8. No other engine type has this issue.
A crossover on a V8 helps to equalize these extra-wide pulses and low pressure areas, and helps the tuning for both banks.
Well-designed unequal-length headers can reduce this effect, and make it disappear altogether in a narrow RPM band, without a crossover.
Equal-length headers ALWAYS benefit from a crossover.
The shorter the crossover is, the more effective it is.
An "X" crossover gives the ultimate in balance, but causes all 8 cylinders to exit through both tailpipes.
Some exhaust makers (like Flowmaster) make an "H" crossover that is of zero length. The two pipes run parallel to each other, with no more than a welded hole between them at one point. This is done to get the maximum balance, while minimizing the actual crossover of exhaust flow between pipes.
I can't way whether a "zero-length" "H" is better than an "X." Flowmaster must think it matters. Or maybe it just gives them the sound they want. All I can say for sure is that the shorter the crossover is, the better.

 

[oldtinsmith]

GBF Pals,
Of all the reading and research I've done so far, I can make two definitive conclusions:
1) Independent dyno testing of crossover pipes ("H", "X", and "Y"), not a single one lost power from a true divided dual exhaust system!
2) Crossovers WILL reduce sound to some extent!
a) "H" pipes tend to have a lower mellow rumble
b) "X" pipes tend to have a higher unique sound (One guy said it reminded him of the sound that 180* headers make

So,,,,,,,,,,,,all I can say (IMO), do alot of research, don't put to much faith in a manufacturers testing, and ask yourself if the research time, the cost (to buy the parts/pay to have them installed), and your own testing, is worth such a little gain in power! Could your money be better spent elsewhere?

Doug

 

[SScamino]

GBF Pals,


So,,,,,,,,,,,,all I can say (IMO), do alot of research, don't put to much faith in a manufacturers testing, and ask yourself if the research time, the cost (to buy the parts/pay to have them installed), and your own testing, is worth such a little gain in power! Could your money be better spent elsewhere?

Doug

That's what I said twice and it's such great advice it should be said again! great post oldtinsmith!