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Old 06-18-2002, 10:14 AM   #1 (permalink)
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Hi -
I am in the process of getting quotes for my dual exhaust on my V8 65 Mustang, and everyone I have called (3 people) have said that an H-pipe is the biggest "exhaust myth" around in terms of high flow (I guess). They all said they would run separate pipes for each side and have no cross over pipes anywhere because it is not necessary. So why do people use H-pipes instead of running separate pipes the whole way down? Wouldn't separate pipes be more efficient for air flow? Would separate pipes sound different than if an H-pipe was used? Would one be louder than the other?

thanks for any advice!
Dan
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Old 06-18-2002, 10:25 AM   #2 (permalink)
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I believe the joining of the pipes helps to scavenge the exhaust gases, it also makes for a smoother tone. I have an issue of hot rod, where they did a test on a hopped up chevelle, with open headers, an H-pipe, and an X-pipe. The most power was made with open headers, followed by the X-pipe, and then the H-pipe. I changed my exhaust from true duals to an X-pipe, and really noticed a difference. My car idled a little smoother, and had a more pleasant tone. I believe you can get 5-10 HP from an X-pipe, don't quote me on that, but I heard it somewhere. Good luck with whatever you decide.
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Old 06-18-2002, 10:25 AM   #3 (permalink)
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I have a Bassani X-Pipe on my 5.0 and a Dr. GAS X-Pipe on my BOSS. I like the sound of both, not to mention the improvement in performance. The X lets the exhaust pluse take the path of least resistance which inturn lets the engine breath much easier. Better flow, more go. IMHO
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Old 06-18-2002, 10:37 AM   #4 (permalink)
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One of the reasons stated by the DMV where I grew up was that without some form of "equalizer tube" you could have serious problems if one of your pipes were to become plugged. It seemed silly to me then and still does.

I have been told by multiple exhaust experts that a properly installed X-pipe is good for between 10 and 30 HP, but it has to be put in correctly.

I have also heard the difference. I would run an X-pipe if I could, just because it makes the car sound so cool. When you get things right and the pipes start singing it is a thing of beauty.

I don't have room for either an H-pipe or an X-pipe and wish I did.
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Old 06-18-2002, 10:37 AM   #5 (permalink)
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Non-crossover exhausts tend to sound "raspy" and uneven. H-pipe or X-pipe smooths things out, balancing the exhaust pulses between banks.

I went from an H to an X, and there is quite a difference in tone & smoothness. It sounds really wicked from about 4000 rpm up, as it completely changes pitch [cold chills] ...

Below is an excerpt from an article I saved awhile back. It's not my writing, but I don't recall the source.......

H- and X-tubes for dual exhaust--
H-tubes balance the backpressure between the two sides of your engine, and even out the complex pressure waves that are flying around in the pipes. The result is enhanced low-end torque, better overall performance, and better sound.
Why?
With a V8, there are always two cylinders on each side of the engine that fire within 90 degrees of each other. On a small-block Chevy, the firing order is 1-8-4-3-6-5-7-2, and the cylinders are numbered from front to back down the crankshaft. Odd numbers on one side and even numbers on the other. A cylinder fires every 45 degrees of crankshaft rotation.
So by looking at the firing order, you can see that cylinders 4 and 8 fire 45 degrees apart on one side. Then later, cylinders 5 an 7 fire 45 degrees apart.
This creates a high-pressure pulse that inhibits smooth flow and makes for a "choppy" exhaust sound. H-tubes and X-pipes equalize this pressure pulse, smoothing out exhaust flow and sound, thus helping your torque output. X-pipes do a better job of this than H-pipes, because there is no distance separating the pipes with an X. But some cars, like my 'Bird, have no way to fit an X underneath.
H-tubes should be at least 3/4 the size of your exhaust pipes, and located in the "hot" area of the pipes behind the header outlets. To find that hot area, one suggestion is to spray a line of ordinary white paint down the pipes after the headers, and go for a good run. Install the H-pipe somewhere in the area where the paint burns off the pipes, equal distance from each header collector. Use the same technique to determine where to place an X-pipe.
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Old 06-18-2002, 10:39 AM   #6 (permalink)
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I agree with the previous 2 posters. Everything I've ever read has showed a 5 to 10 hp gain adding a crossover, with anecdotal information that the exhaust got quieter while making more power.

When looking at your '65 though, by far the biggest difference you can achieve in power is going to be related to replacing the log style stock exhaust manifolds with something better. What would be better? Almost anything. The hypo exhaust manifolds are a lot better than stock, shorty headers would be better than that, and long tube headers would be even better.

I'm unclear with where your exhaust shops are coming from, but maybe YOU WOULDN'T see any benefit with the crossover with the highly restrictive stock exhaust manifolds? I don't know. Personnally I'm running long tube headers into a 2 1/2" exhaust with a custom built 2" crossover (H pipe) and 3 chamber flowmasters. Seems to work well.

Good Luck!

Phil
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Old 06-18-2002, 10:41 AM   #7 (permalink)
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Ok I'm about to show my age.....
The H pipe was originally used to reduce the bbrrraappp that you would get from glasspacks. Then, it was discovered that it equalized the pressure if placed right and would reduce packpressure (but to find the right spot took a lot of testing). The X pipe is clearly the way to go by comparision. Either can be built by a shop or yourself....they're easy. One way to tell where to put center point of the X or install the H, is to take high temp spray paint and put a light coating on each pipe. Driver the car to get the pipes hot, then look for where the paint is bubbling off.....that's where it goes!
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Old 06-18-2002, 10:43 AM   #8 (permalink)
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How does this work on a late 5.0L HO engine with firing order 13726548?
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Old 06-18-2002, 10:46 AM   #9 (permalink)
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Just the same, even with Tri-Y headers. (Mine is an E303 cammed 5.0).

If you've heard a newer Roush GT with side exits, that's the sound....

On the 13726548 firing order, you'll note that 1&3 (right bank), and 6&5 (left bank) fire consecutively. On the 15426378 firing order, 4&2 (R), and 7&8 (L) fire consecutive. Without a crossover, you get that "popping" sound from either firing order.
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Old 06-18-2002, 10:56 AM   #10 (permalink)
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The reason for the H or X pipe is to increase the effectiveness of scavenging. Every time a cylinder fires and the exhaust exits the combustion chamber, there is a pulse of gas flowing through the exhaust system. Every thing you can do to help the pulse of gas exit will increase performance. The gas will flow better if it can maintain a high velocity and have smooth bends. A really neat trick to help the gas out is to leverage the low pressure (not really a vacuum but close) just after one of the other cylinders has fired to “scavenge” the exhaust out of the cylinder. If you can get very effective scavenging and depending on the cam your running, you can “pull” the fresh air/fuel mixture into the cylinder. Long tube headers, Tri-Y headers, H and X pipes are all tools to increase scavenging. A well-tuned normally aspired motor (correct combination of intake, heads, cam and exhaust) can have a volumetric efficiency of over 100%. In comparison, most street motors are running around 60 to 70 % volumetric efficiency. If you’re after a performance edge then I would recommend working with a shop that knows what they’re talking about. Else, if you just want to cruse on Sunday afternoon, then it really does not matter much. Good luck and have fun.
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Old 06-18-2002, 11:16 AM   #11 (permalink)
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I agree with all of the above and wish to add that ceramic coated headers also seem to help in this process; my guess is that the exhaust pulses stay hot longer, keeping the pulse velocity up longer which helps scavange the each pulse that follows. Also moves the heat out of the engine compartment and avoid killing electrical and rubber things like your starter, etc.
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Old 06-18-2002, 11:25 AM   #12 (permalink)
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I would like to add that all the dual exhaust (true duals) in late model cars include a cross-over pipe in them.
Perhaps the exhaust guys you are speaking to desire to do less work. Or like the popping sound of the straight design.
Get a cross-over installed if at all possible.
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Old 06-18-2002, 11:29 AM   #13 (permalink)
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O.K., it seems we all agree on the benefits of the X-pipe. In real life, where does usually mount. It looks like under the tail shaft of the transmission might be best.
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Old 06-18-2002, 11:50 AM   #14 (permalink)
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The tail shaft area seems to fit better due to more room but from a performance perspective, closer to the front of the transmission but behind the bell housing is usually better. It depends on your set-up. Nothing like a clear answer!
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Old 06-18-2002, 12:19 PM   #15 (permalink)
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The farther forward you can install the X-Pipe the better.
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