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
SHORT answer, unless your running a very low restriction exhaust or no exhaust past the collectors theres unlikely to be a significant differance between true tunned headers and most commercially available street headers as the restriction tends to kill off the benefits, yes with open exhaust theres gains to be had, with a tunned header, but unless the compression,displacement,cam timing and intake design match, those gains the correctly designed header can produce are hard to see.
IN most cases when your running an exhaust system behind the header collectors the restrictiion to flow kills off some of the benefits, ANY significant BACK PRESSURE HURTS the effective scavaging, the header scavaging was supposed to provide. HEADERS are supposed to be designed to increase cylinder scavaging ,thus increasing the next cylinders volumetric fill efficiency, that boosts torque due to a larger percentage of the fuel/air mix being available to burn and produce cylinder pressure,thus producing power, but unless the cam timing and intake design are roughtly matched to that same rpm band they can,t effectively scavage the cylinders.
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.
theres not much sence in paying a great deal more for a true tunned exhaust header unless your willing to match the other components to the combos intended rpm band and the cars gearing keeps you in that rpm band!
http://www.engr.colostate.edu/~allan/fl ... /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
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 restriction to flow past the header collector would be very similar to running open headers and the main function 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 by increasing the cross sectional area of the exhaust path,and blend and cancel out the pulses that make the noise
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.
you might also consider the fact that flow restriction tends to increase with the rpm band, your stock exhaust is probably fine at the 1500rpm-4000rpm band it was designed for but when your expecting to zing the rpms up in the 4500rpm-6500rpm or above range the headers and collectors, and exhaust behind them,that are used effect a much bigger part of the potential power curve
__________________
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
SHORT answer, unless your running a very low restriction exhaust or no exhaust past the collectors theres unlikely to be a significant differance between true tunned headers and most commercially available street headers as the restriction tends to kill off the benefits, yes with open exhaust theres gains to be had, with a tunned header, but unless the compression,displacement,cam timing and intake design match, those gains the correctly designed header can produce are hard to see.
IN most cases when your running an exhaust system behind the header collectors the restrictiion to flow kills off some of the benefits, ANY significant BACK PRESSURE HURTS the effective scavaging, the header scavaging was supposed to provide. HEADERS are supposed to be designed to increase cylinder scavaging ,thus increasing the next cylinders volumetric fill efficiency, that boosts torque due to a larger percentage of the fuel/air mix being available to burn and produce cylinder pressure,thus producing power, but unless the cam timing and intake design are roughtly matched to that same rpm band they can,t effectively scavage the cylinders.
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.
theres not much sence in paying a great deal more for a true tunned exhaust header unless your willing to match the other components to the combos intended rpm band and the cars gearing keeps you in that rpm band!
http://www.engr.colostate.edu/~allan/fl ... /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
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 restriction to flow past the header collector would be very similar to running open headers and the main function 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 by increasing the cross sectional area of the exhaust path,and blend and cancel out the pulses that make the noise
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.
you might also consider the fact that flow restriction tends to increase with the rpm band, your stock exhaust is probably fine at the 1500rpm-4000rpm band it was designed for but when your expecting to zing the rpms up in the 4500rpm-6500rpm or above range the headers and collectors, and exhaust behind them,that are used effect a much bigger part of the potential power curve
__________________
