fabricating an (H) pipe in the exhaust

[grumpyvette]

IF your fabricating an (H) in your exhaust

 

 

http://www.metalgeek.com/static/cope.pcgi

 

this calculator above will prove helpful

 

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?function=Search

 

ITEM 37354-9VGA

 

OR you can buy a pre welded kit

 

http://www.jegs.com/p/JEGS/751638/10002/-1/11525

 

another little tip when fabricating the center of the (H) connector pipe is to use two sections of pipe aboit 1" longer than 1/2 the distance between the main exhaust pipes in length,with the ends modified (fish mouthed using the calculator above)to intersect the main exhaust, and then expand one of the un-modified ends to telliscope inside its twin, thus the angle of the cut axis and length of the ends is semi-adjustable making it far easier to fit and weld.

and use a hole saw thats one size smaller to cut the holes in the main pipe that your welding the ends of the (H) over

[blueovalz]

Thanks for the tips. I'm planning on adding the H-pipe some time this summer, and the template will come in handy. I'm looking for data on where the H-pipe should be located optimally. I'm very limited on its location and concerned it will be placed too far rearward to be fully effective.

[grumpyvette]

just like when adding an (X) the (H) should be placed as close to the header collectors as the clearances under the car permit to reduce exhaust flow restriction, the idea is to basically ballance the flow rates and reduce the potential back pressure, in the exhaust to increase the cylinder scavaging by doubling the cross sectional area the exhaust flow occupies as it exits, thus reducing the flow restriction.

A properly designed (X) is less restrictive and more effective but in many cases clearances under the car make an (H) far easier to fabricate and install.

[bigblock96]

ha ha yea bought one of those for harbor freight and broke it on the third pipe took the pipe to the local muffler shop and used his hyd.expander for a coke.much easier and for better performance go with the X rather then a H jmo I am working on a quad exhaust now and going to be fun oh and sorry not on a z sorry it's still a 6 banger.it's on the attached pic.

[bjhines]

I am in the process of designing my exhaust system right now.

 

Welder, chop-saw, band-saw, tubing notcher, sander, tailpipe expander, and a BFH.

check!

 

 

Mandrel bends, straight tubing, ball couplers, header flange adaptors, all in 2.5" aluminized steel.

check!

 

 

The S-30 does not lend it'self to putting an X-pipe anywhere in front of the tranny mount. I could put an H-pipe closer to the tranny bellhousing. I could put BOTH and X and an H- pipe in the system.

 

Would this be a waste of effort???

 

Does the H-pipe equalize the pulses to the extent that a downstream X-pipe no longer functions as it should?

 

Does an H-pipe really need to be as large as the main pipes? My BMW M3 has only a 1" H-pipe dia. Many systems in factory cars use a large dia. H-pipe but only have small(1" dia.) holes in the main pipes to feed the H.

 

If the goal is to get the H as close to the collectors as possible then I could run a crossover tube directly off the header collector flanges. If the H-tubing only needs to be 1" then this would be easy to do. What about "collector length" tuning?... wouldn't this effectively cancel out the rest of the system as far as collector length tuning?

 

How does H-pipe dia. and length effect the operation of the H-pipe system. Is is possible that using a larger dia. H-pipe with a smaller hole in the main tubing was a consideration for pulse tuning or reversion.

 

I would assume that you would eventually reach a point where you have a "zero loss" exhaust system like the ones using the chamber to terminate the collectors instead of constant dia. tubing. Those systems do not place an H-pipe as close to the engine as possible. I was under the impression you needed 1-2 feet of collector tubing at the very least for most V-8 applications.

[grumpyvette]

"I could put BOTH and X and an H- pipe in the system.

 

Would this be a waste of effort???

 

Does the H-pipe equalize the pulses to the extent that a downstream X-pipe no longer functions as it should?"

 

 

if you place TWO it tends to mellow the exhaust tone and reduce resonance in the car and depending on the location and pipe dia. and length it usually does help the cylinder scavaging a bit more than one alone, but again the closer to the exhaust headers the better off youll be and ideally the (X) should be closer to the engine than the (H) but that being said up front, I installed an 3"(H) just behind/under the bellhousing rear , where the headers ended,and a second 3"(H) just in front of the mufflers on a friends GTO 3" full exhaust and a very nice rumble/lopey idle and a good wide power curve for his 455 pontiac was the result, were both pleased

 

you may want to keep in mind the HEADERS and the primairy diam. amd length and the collector design are what effects the cylinder scavaging , the exhaust past that is basically designed to supply a level of noise reduction and a low resistance to flow path for the exhaust to safely exit the car, if the headers are designed correctly the engines exhaust system past the collectors just needs to be designed to reduce noise and provide that low resistance exit path.

the (H) or(X) reduces the restriction to flow and blends the exhaust pulses to reduce the noise, if the exhaust past the collector does act as a collector extension on the headers is usually a bit smaller and restrictive than ideal.

in an ideal world the restiction to flow past the header collector would be very similar to running open headers and the main funtion of the exhaust would be only noise reduction, and exiting the exhaust where it would not re-enter the crew compartment. but the truth is most exhaust system pipes are too small in dia. to allow that so the (h) or (X) provides a way to reduce flow restriction and blend and cancel out the pulses that make the noise

[madkaw]

here's a pic of my X pipe and it's location. I placed mine for convience and room. Of course my application is for the L6 ,and I had to use room to get the pipes located in order to make an X. No real science here, I used a MSA header with unequal length pipes so I made the longest run to the X pipe come from the shortest collector pipes. I tried finding a pre-fab X pipe , but most were 2.25 or 2.5 inch and my pipes were 2", so I made my own which worked out since this was completely custom. I am not saying that I know what I'm doing, just some input. There is a lot of talk about 2 pipes for inline 6's and wave pulses and such, I thought the X pipe was the best possible solution for good sound and flow. Hope it works!!!!

[bigblock96]

yes both H-and X- will be time not well used and keep that BFH handy you will want to use it on numerous occasions

and as for exhaust pulse and such you will need to figure in so many variables as primary i.d , length,valve overlap , collector i.d. and length and on and on.there is a piece I had somewhere discussing it all I will see if I can find it.

[bigblock96]

http://tinyurl.com/32m9mb this gives a lil about header design.

a lil more-from SCM

To get the best breathing and to help pull as much fresh fuel/air mixture into the cylinder as possible during the overlap period, it is best if a low-level vacuum or rarefaction can be created and maintained past the initial low-pressure wave in the primary pipe. A well-designed header can use acoustic energy to maintain low pressure near the exhaust valve during the overlap period.

 

Four-into-one headers typically work best over a relatively narrow powerband. Like anything, there are exceptions, and this particular AEBS header had excellent low-rpm performance as well.

 

The way a header is tuned is much like how an organ pipe is tuned. The optimal length used is the one needed for the primary pipe to have a fundamental note corresponding to the time when the exhaust valve opens. When the exhaust valve opens, a high-pressure pulse of hot, expanding exhaust gas travels down the exhaust port at approximately 300 feet per second. This wave of hot, moving, high pressure gas has mass and inertia of its own which pulls a suction or a low pressure rarefaction behind the pulse.

Depending on the engine, the pulse can have a positive pressure of anywhere from 5 to 15 psi with the low pressure rarefaction behind the pulse being anywhere from 1 to 5 psi of negative pressure. As this low-pressure rarefaction is several milliseconds behind the initial high pressure pulse, it can be exploited to help suck residual exhaust gases out of the cylinder toward the end of the exhaust stroke as the piston approaches TDC. The build up of this negative pressure and its timing in the exhaust stroke is closely associated with the primary pipe's length and diameter, just like an organ or other musical instrument.

 

A standard, low-cost collector like this one can still be effective, but ultimately does not flow as well as a true merge collector. This type of collector can be extremely restrictive if carelessly designed and constructed.

 

As the exhaust valve starts to close and the intake valve starts to open, the engine enters the overlap period. During the overlap period the piston is starting to slow down as it approaches TDC and gets ready to reverse directions. To maintain good scavenging, a negative pressure must be maintained near the exhaust valve to help continue to suck stale exhaust gas out of the cylinder to make room for fresh fuel and air. As the main column of high pressure gas is almost out of the end of the header's primary tube, the pressure near the exhaust valve starts to rise again. All is not lost, however.

As the pulse of high-pressure, high-energy gas leaves the end of the primary tube and is diffused in the larger diameter header collector, a reflected pulse of sound energy just like a musical note is generated, much like that of a organ. This reflected sonic pulse travels down the exhaust pipe at the speed of sound, which is usually around 1100 to 1900 feet per second in thin, hot exhaust gas, causing a slight rise in pressure at the valve. The wave is then reflected back toward the open end of the primary pipe. Just like the initial exhaust pulse, the reflected sound pulse has an area of rarefaction, or low pressure, behind it. If the pipe is of proper length and diameter, this reflected wave can be exploited to lengthen the amount of time the condition of low pressure exists around the exhaust valve.

These phenomena are harnessed by the smart header designer to tune the pipe to help get the maximum amount of burnt gas out and to help pull the most fresh fuel in. Of course, because a header is tuned like a musical instrument, a header can only be optimized to produce the greatest scavenge-improving vacuum in a band of several hundred rpm.

Without going into a lot of math, there are some general guidelines you can use for selecting a header. Shorter primary runners and/or larger-diameter primary runners are better for top-end power. This has to do with the tuning of the pipe's fundamental note for reflected wave tuning and the travel time of the main initial exhaust gas pulse. Just like a piccolo is a higher-pitched instrument than a clarinet, a shorter, fatter primary pipe is better for higher rpm. Conversely, a longer and/or smaller diameter primary tube is better for lower rpm for the same reasons as above. Camshaft design and the duration of the exhaust cam are a large factor in header design. Generally, the later the closing point of the exhaust valve, the shorter the header primary pipes must be.

The way the primary pipes gather together is important also. This area of convergence, called the collector, is critical for proper header function. It must be of larger diameter than the primary tubes because it must be large enough to acoustically represent the end of the pipe (this is necessary to get the reflected sound wave to help scavenge the exhaust), and it must be big enough to support the flow from all the cylinders without creating excessive backpressure. Usually the collector is just a junction where all of the pipes are stuffed and welded into a larger pipe that may or may not neck down into the final size of the exhaust pipe. A well-designed collector, pairs cylinders opposite in the firing order with each other so an exiting pulse from one cylinder will not hamper the evacuation of the next cylinder. Adjacent cylinders in the firing order are kept separate so the exiting pulse of one cylinder cannot contaminate the next cylinder that may be on the overlap part of the power stroke. In a typical inline four cylinder, that would mean paring cylinders 1 and 4 and 2 and 3.

The best collectors are called merged collectors. This is a collector where the two opposite cylinders are paired together in a smooth taper before being introduced to the flows of the other cylinders. Merged collectors usually produce a wider powerband

[bigblock96]

hahaha and more-

• The Evolution of the X-Pipe
  To understand the importance of the X-pipe in relation to improved performance and power, you have to know about its roots. The X-pipe is really the offspring of the H-pipe design, which was first conceived in the 1960s by the major American car manufacturing companies at the time. Duel exhaust pipes for V-8-powered vehicles are very noisy, as there is no sound wave cancellation between the 2 separate four-cylinder engines and unconnected exhaust systems. Engineers were looking for a way to cut down on interior noise levels and improve the engine's power. They realized that running a balance tube between the two branches of exhaust pipe would work to broaden the torque curve (thus improving engine performance) and dissipate sound resonance in the exhaust system.
   
  In the 1990s improved technological advancements made it possible to construct an exhaust pipe that, instead of connecting by means of a balance pipe at a severe 90-degree angle, could unify the two branches of pipe to create a flow of exhaust in one direction. Now X-pipes are being manufactured for popular performance cars, usually off-road versions minus catalytic converters, but you can also find them in legal models fully equipped with proper emissions equipment. Performing an X-pipe mod is an option that you should consider.
  
• Why X over H?
  It has been proven time and again that the X-pipe design is more efficient than the H-pipe. Various tests have shown that for multiple cylinder engines the X-pipe outperforms H-pipe exhaust systems, especially as rpm increases, providing both better torque and power. Unified exhaust pipes work most efficiently with multiple cylinders because of the scavenging effect. With exhaust X-pipes the almost seamless connection between the two exhaust pipes allows sequential firing cylinders to salvage any spent exhaust gases from the combustion chamber more efficiently and creates more room in the cylinder for a fresh intake of undiluted fuel and air. When you have two exhaust pipes, as the velocity in one header tube increases, the pressure in the adjacent tube is lowered causing the exhaust to be sucked out of that cylinder. X-pipes are simply better at doing the job, especially at higher speeds.
  
• Installing Exhaust X-Pipes
  This is a simple mod that almost anyone can perform successfully. Most companies produce exhaust X-pipes that are simple bolt-ons that can be installed in less than an hour using the usual hand tools.
   
  If you own a vehicle that doesn't have an X-pipe available, it is possible to have a custom X-pipe assembled for you. A muffler shop can construct it by taking an X-pipe union and bending up some exhaust tubing until it fits. If you decide to make your own exhaust X-pipe from scratch, so-to-speak, remember to place the X-pipe union as close to the rear of the vehicle as you can to increase the power.
  
• A Brief How-To
  To install exhaust X-pipes, first begin by positioning the passenger-side header pipe in place and tightening it before moving on to the next step. Make sure it is secure. Now, fit in the actual X-pipe along with the driver's side header pipe. Remember that the long leg of the X must go toward the front driver's side of the car. Now it's time to fit the pipes of the X into position and loosely attach them to the after-cat system. You might have to adjust how the after-cat is hanging for proper tailpipe positioning and tuck up the X-pipe square. On some vehicles the tranny crossmember has an exhaust hangar - if this is the case you can tack the hardware onto the pipes. Tighten the bolts and tack-weld the junctions at the X. Check everything one more time before removing the X-pipe and welding the full length of the junctions. The assembled unit now needs to be bolted back into position - simple as that.

All in all, with exhaust X-pipes torque and power will increase resulting in fast acceleration, improved fuel economy and a nice quiet ride. The difference is noticeable with the installation of X-pipes on a V-8 engine - interior noise is reduced considerably because you don't hear the firing impulses of 2 four-cylinder engines, but instead hear the noise of all 8 cylinders blasting out of both pipes at once.

[bjhines]

ok.. What about H-pipe diameter and length? what about the hole in the main pipes being smaller than the H-pipe dia.

 

The H-pipes in most factory applications are only 1"-3" long. My BMW has a 1" long H-pipe that is only 1" dia as well.

The H-pipes on corvettes were at the rear end of the system and they were also very short(3" long) and the holes in the main pipes were only 1" dia. even though the H-pipe was more like 2.5" dia.

 

I ask this because an H-pipe under the bellhousing will be considerably longer than an H-pipe further back in the system. If I used a small dia. H-pipe it would seem that length would be even more critical.

[grumpyvette]

the IDEA of the (H) pipe is to allow some of the flow mass in the orrignating flow route to exit the original exhaust thus lowering the resistance,to flow the restriction presented by the single pipes cross sectional area provided,and pressure dropping off,and due to a significant percentage of that mass exiting and taking the lower resistance secondary route lowers pressure and the disruption of the sound waves tends to lower the sound of the exhaust also.

keep in mind properly designed headers and collectors provide the cylinder scavaging and there length and dimensions are calculated to maximize that scavaging effect the exhaust past the collectors is basically designed for noise abatement and safely exiting the exhaust gases.

you get very little scavaging effect from anything past the collectors if the systems designed correctly

[bjhines]

I have a decent understanding of acoustics, and fluid dynamics.

 

As the high pressure pulse travels down the collector extension it passes the hole for the H-pipe. Some of the gas flows into the H-pipe thus dissapating the peak pressure of the pulse as it travels down the rest of the exhaust system.

 

This would seem to reduce the effectiveness of scavenging on the X-pipe further down the system. There is less differential pressure in the X-junction due to reduced peak pressure in the pulses that have already passed the H-pipe.

 

The H-pipe can also be "tuned" to ensure there is a low pressure peak at the other end of the H-pipe when the next pulse comes down the opposite side.

 

 

Grumpy says that the X is effective because it provides a dual path for the pulse to dissapate into.

Others tout the fact that there is a low pressure trough in the opposite pipe when the next pulse comes to the X. This would be scavenging in much the way a 2-cycle engine uses a convergent/divergent cone as a resonator to improve scavenging.

Hot-Rod magazine has done similar write ups and offer slightly different explanations than the sources in this thread.

 

I also understand that the acoustic pulses tend to travel through the moving gases much faster than the actual gas medium is moving down the pipe. Bends, restrictions, H and X pipes, variations in diameter, converging/diverging areas all effect acoustic properties differently than the fluid flow properties. There are two completely different sets design principles working in any exhaust system.

[grumpyvette]

theres plenty of fluid dynamics math and research out there to show that the distances the exhaust travels between exhaust pulses and the diam. and length are easily calculated, and past that length the second previous pulse has little effect compared to the current and previous pulse energy and reflective wave

and lets not forget the cam timing displacement and intake port all effect the cylinder scavaging the headers can effectively provide also

 

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

 

http://www.rbracing-rsr.com/runnertorquecalc.html

 

http://victorylibrary.com/mopar/header-tech-c.htm

 

http://www.headerdesign.com/

 

http://www.pontiacracing.net/js_header_length1.htm

 

http://www.slowgt.com/Calc2.htm#Header

 

example , my 383 vette has a cam with exhaust cam timing that opens at 83degs bbdc, thats 97 degs atdc, http://www.cranecams.com/?show=browseParts&action=partSpec&partNumber=119661&lvl=2&prt=5

Bore: (Inches) 4.03"<BR>Exhaust Valve Opening Point: (Degrees ATDC) 97 degs

Peak Power RPM: 5500rpm Calculated information appears below

Header Pipe Diameter: (Inches) 1.84"<

Header Pipe Length: (Inches) 37.65

Collector Diameter: (Inches) 3.5

Collector Length: (Inches) 18.82

 

 

so ideally the (X) is placed at that point to maximize scavaging but thats not always possiable due to clearance, and if you choose to place an (H) just before the mufflers its mostly to reduce resonance or noise not increase scavaging but it tends to reduce the restriction to flow

[bigblock96]

true X will sound a little bit off as a H will give you that deeper tone but as for performance it's so so.and don't we all wish we had a dyno in the garage too!!

[grumpyvette]

most guys I talk and deal with,seem to think that slapping a set of headers on thier car is all thats required to boost performance....ANY HEADERS! ...and they fail to realize that both the header design and the exhaust system behind them require a good deal of thought if you want the maximum benefits, and that simply hooking a restrictive exhaust system to the collectors on the best headers will negate most of thier potential benefits.

most commercial headers are designed mostly for ease of manufacturing and ease of installation,little thought goes into maximizing the cylinder scavaging which is thier main function.

your fooling yourself if you think headers will provide a big boost in hp/tq without the low restriction exhaust behind them,and in most cases that requires a larger dia. exhaust system and adding an (X) to the system and extending the header collectors at thier full dia. up till at least the exit of the (X) so the twin exhaust pipes cross sectional area can provide that reduced restriction to flow, rather than the reducers many guys install to the collector exits to adapt them to the stock exhaust system

 

example of a well laid out exhaust (MELROSE)

 

but even that system could be hurt if you slap restrictive mufflers on it

[bjhines]

Hey... You copied me!!!!!

 

Here is mine just complete.

 

 

 

I decided to use an X-pipe instead. Maybe I'll add an H-pipe too.

...

[Savage42]

This is the X-pipe I'm going to run with dual exhaust all the way back to a dual 2.5" in and 3" out Magnaflow muffler.

 

[pparaska]

The X-pipe makes the engine sound very even compared to an H-pipe, in my opinion. There's a full write-up of how I built it a 2.5" dual system with an X-pipe behind the transmission crossmember here: http://alteredz.com/exhaust.htm

 

I bought the X-pipe from Dr. Gas, as I didn't trust that I could weld up a good one myself. Maybe if I had a TIG welder and was decent with one...

 

If I were to do it again, I'd would build it with slip-joints instead of flanges. I used the large Dynomax Hemi Turbo mufflers to try to maximize muffler volume to get good flow and sound reduction.

 

The exhaust is not too loud for most people's taste, and it has a deep sound. At above 2500rpm, it sounds very even, unlike many V8's - I believe the X-pipe is to thank for that. It sounds a bit like a muffled NASCAR engine at WOT and some rpm. I'd not do an H-pipe on any car as the only crossover pipe if there were space for the X-pipe. The idea of multiple X- or H-pipes is interesting though!

 

Here's the system after I had it coated almost to the mufflers:

 

(I'm not using those headers any longer - I've moved to Sanderson/JTR angle plug type block huggers with D-ports for the Canfield heads. I still would love to do a long tube header, but they would have to be custom as I don't like the way the street rod header that some have used hang so low.)