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Exhaust Pipe Genius Required.
Is there any body in "Cobra Land" who knows the benefit or otherwise of joining the 2 exhaust pipes with an "X" or an "H" pipe on an under body system? I looked on Wikipedia and it tells me there is a benefit in reducing back pressure but which is preferable? Logic tells me an "H " pipe would create a venturi effect as the gases passed the bar of the H, whereas I would imagine the gases getting turbulent as they collided in an "X" join. Any theories, (or links to authoritative web sites) would be appreciated. Thanks Peter.:confused:
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A V8 is only firing one cylinder at a time and usually on alternate banks (depending on the firing order). That means on a true twin system that there's a fair bit of dead time in the exhaust system between pulses. By joining both sides together with some kind of cross over you are effectively doubling the flow of your exhaust. Each pulse can travel down both sides of the system.
From what I've read the X pipe flows better than a H pipe. The gasses aren't having to do a right angle turn to travel up the other side of the system. Just like a properly designed collector the X pipe can actually have a scavenging effect on the other side of the exhaust system. The H pipe is easier to install as the two sides of the system don't have to converge together. Each has their pluses and minuses. Hope this helps. Cheers |
Thanks Mike. I have continued searching and found an exhaust mob that explain it the same way, worth a look if anybody else is interested, lots pictures too.
http://www.surefloexhaust.com.au/frame1600x1200.htm Click on "X Pipe" |
And in simpler (simplest) terms,
A "H" piece is more like a header A "X" tube is more like an extractor. A full twin system has more noise from nodal and antinodal pressure waves. A H pipe is really a good pressure balancer. An X pipe more of a flow and pressure equaliser. I did play with some bigger valveless pulsejets a while back and gas flow dynamic stuff can become real heavy real quick. But, it was worth the look and the noise. |
Some pic's of my x pipe setup on my website.
Link to the page is http://www.comdotau.com/gall/index.p...obra%20Exhaust Old mate did a good job of fitting it all at road sensible height considering the limitations. |
Thanks Outwest, do you know how big the hole is where the pipes meet? Peter.
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Basically the two pipes were sat side by side and the touching points marked around with a felt tip marker. Then he cut them and adjusted the joins moreso than the actual size.
To make a comparison I would say its more or less similar to an egg size/ shape. I think the size of the hole would depend on what angle your pipes meet. Each good exhaust shop would do an X pipe mod quite easily. |
I don't know of any american V8 that fires on alternating sides of the block through all 8 cylinders. During 2 revolutions (all cylinders fire once) two cylinders on the left side fire in order and 2 cylinders on the right side fire in order. Because of this we tend to get high pressure pulses on one side and then the other. Take a look at the exhaust setup on the old Ford GT40s, you will notice the headers are arranged so that the pulses always alternate left/right/left/right etc.. This was done to extract every last HP available. The closest thing to this on the street is the "X" pipe seen on most undercar V8 exhaust systems. It's the poor man's GT40 exhaust setup. By using an X pipe (or less so an "H" pipe) we can extract a little more HP by providing a little more scavenging of the exhaust gases.
Bob Windsor 1,3,7,2,6,5,4,8 Others 1,5,4,2,6,3,7,8 |
An X pipe or H pipe make the car sound better, . . . . more mellow and deeper and less raspy than just two straight pipes. They enhance low end torque quite a bit, but have little effect on upper rpm power.
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Help
Sorry to highjack your thread, but how do you start a new thread?
I'm new, and I don't know how this works yet. Any information would be appreciated. Thanks so much. Wonzingy |
Go to "forums", find a region or whatever, click on "new thread".
Bob |
Posting
Thanks for your information.
Wonzingy |
It's a popular misconception that an X-pipe creates 20-30 more HP vs. no crossover or an H-pipe. Personally, I don't like the way X-pipes sound, plus the setup momentarily merges all the exhaust into a single flowpath, which sounds funky. H-pipes sound much better IMO, & there is either none to very minimal gains by using an X-pipe. Two Ford engineers that I used to talk with periodically did tests & studies on this very subject for about a year, & they concluded there was nothing magic about any X-pipe setup.
Also, if you are going to do an H-pipe, the crossover pipe should be about 70% of the diameter of the rest of the exhaust. The crossover should be situated at the "hot spot." |
This is the set up on an original GT40 near me.
Merv http://www.clubcobra.com/photopost/d...T40_Motor1.jpg |
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I suspect it has had a hard racing life
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Thanks Guys! a wealth of information as usual, Regards, Peter
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Rare Iron
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You mention the pipe should be 70% is that a minimum or a maximum, Peter. :confused: |
70% is the supposedly ideal size. Find the hot spot by painting the inboard areas of the opposing pipes. Then run the engine & watch where it bubbles first.
The G-spot is much more tricky - I don't have answers for that. |
Thanks for that info. I'll probably run two separate pipes initially and sort out the crossover pipe later, as the car is not running yet. Peter
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