anti reversion exhaust design



anti reversion exhaust design

Postby grumpyvette » November 26th, 2008, 12:25 am

Ive played around with different versions for years, results vary with the design features and how well the systems thought thru and built, but correctly designed they do get impressive results, badly designed they can hurt performance.
exhaust systems are frequently thought of by many guys as a way to route hot/burnt gases away from the engine and a way to reduce the engine noise, its fairly common for guys to either just slap on a set of headers that are listed as fitting the car the guys using without much thought or if anything is thought thru its simply to look for a low restriction muffler.
keep in mind your cam timing, intake runner design,displacement,compression, and other factors help or hinder the results you'll get.
those hot exhaust gases exit under hundreds of psi of pressure and potentially have a great deal of inertia that can be used to help increase the negative cylinder pressure and significantly increase the intake runner flow rates as flow out thru the properly tuned exhaust header drags in the next intake runner charge during the valve overlap period.
low and mid rpm torque increases are common in a well designed set of AR headers,high rpm power loss is common in badly designed headers
for those that don,t know what were referring to its headers/exhaust designed to flow only in one direction, baffles are designed into the primary and collectors to break up or retard reversion pulses.
your goal is to keep the exhaust speed/energy high to maximize cylinder scavenging yet restriction low to reduce back pressure to the minimum and to control and direct reversion pulse energy to assist in that scavenging.
the properly tuned set of headers matched to a low restriction exhaust and especially if your using a single runner per cylinder stack type injection can , with a correctly timed cam, give amazing results, gains of 40-70 ft lbs or even higher levels of torque can result from tuning both the exhaust and intake runners and cam timing, on a race V8 with high compression and properly tuned components are very common, over and above what a typical single carburetor intake can produce.
generally its done by extending the primary header tubes at some point into a larger primary tube (stepping up, so as to leave a sharp edge that the reversion pulse generated at some rpm ranges has difficulty traveling back over. or installing venturis (tapered cones) in the exhaust headers that accomplish the same effect or BOTH
yes you really do need to read thru the links, and sub linked info


http://www.headerdesign.com/extras/design.asp

viewtopic.php?f=38&t=1002&p=1805&hilit=+curve#p1805

http://www.burnsstainless.com/Xdesign/xdesign.html

viewtopic.php?f=55&t=4502

http://www.vetteguru.com/mods/headers/

http://www.boatheaders.com/reversionbody.htm

http://www.burnsstainless.com/dynosys/dynosys.html

http://www.headersbyed.com/bildbetr.htm

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

viewtopic.php?f=38&t=1002&p=1805#p1805

http://www.headersbyed.com/stepped.htm

as a simple example of a mod that usually gets results if the reduction is smooth/gradual, if its fairly abrupt the reduction acts as a restriction or even causes reversion to some extent

Image

install one of these venturies in the 3" exhaust pipe(small end toward the rear)where the 3" collector mates to the 3" exhaust pipe to form a lip or step in the exhaust so any reversion pulse tends to have difficulty traveling from the exhaust to the collector
adding an (X) just past the anti reversion venturies reduces or at least tends to reduce reversion pulse strength also
Image

http://www.summitracing.com/search/?keyword=exhaust%20cones&dds=1

IF your trying to reduce noise levels, you can buy or fabricate these cones that tend to break up and reduce exhaust noise, once installed in the exhaust, without producing much of a restriction since the total surface area of the mini holes is greater the the pipes cross sectional area
the tabs can be tack welded or sheet metal screw attached, and adding an (X) pipe near the collectors and an additional (H) near the muffler entrance point tends to mellow the tone

Image
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: anti reversion exhaust design

Postby grumpyvette » November 26th, 2008, 1:58 pm

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...ngth/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=brows...61&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
__________________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/d ... ion=Search
Image

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
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: anti reversion exhaust design

Postby grumpyvette » February 18th, 2010, 5:01 pm

Image

Image

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http://www.burnsstainless.com/theory.aspx

http://www.burnsstainless.com/construction.aspx

http://www.burnsstainless.com/stainlesssteel.aspx

anti reversion baffles come in several designs, but placing something similar to these in ratio of size/diam. on each header primary at about 18"-20" from the exhaust port and a larger version on the header collector will significantly increase cylinder scavenging by reducing unwanted reversion pulse strength
If your thinking thats a good deal of extra work, whats the potential gains in performance to justify the trouble?
well thats a valid question and the answer varies wildly with engine displacement ,cam timing,head flow rates.intake design, etc, but on a 13:1 cpr BBC engine with a tunnel ram intake , power gains of an additional 80 ft lbs were recorded in the mid rpm range over other tuned headers, in one test I saw. when they used the primary and collector anti-reversion baffles and had the collectors flow into a common (X) pipe
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: anti reversion exhaust design

Postby philly » December 13th, 2013, 8:00 pm

this is very informative stuff! once upon a time i remember there was an aftermarker cat back piece from walker and later dynomax after the merger that had a crossover pipe connecting the exhaust on the car just after the diff when the exhaust turns to make its connection to the stock muffler location. everyone who used it swore that it eliminated the drone noise from their aftermarket exhausts. performance benefit? irrelevant as we all know those werent really designed with real performance in mind, just mass produced noisemakers that lowered some restriction.
-phil

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Re: anti reversion exhaust design

Postby philly » December 13th, 2013, 8:06 pm

Paul, i don know how much turbo technology youve worked on first hand, but do you think it would be a good idea to incorporate an anti reversion cone setup like the one described above with a turbo setup?

all else being equal i generally like to think of a turbo as a muffler, and although its easy to overcome poor turbo manifold/header designs with more boost, ive always wanted to build on the philosophy of being able to make a great set of tuned headers and channel them to a turbocharger. there has to be even more noticeable gain in this, turbo spooling faster, more responsiveness, quicker e/t's. of course one would have to calculate all the cfm figures for the intake and exhaust based on the amount of air the turbo is pushing into the cylinder.

would an easy way to find that number be multiplying the motors naturally aspirated displacement by the number of atmospheres (actual not gauge) that we would be forcing into the cylinder?
-phil

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Re: anti reversion exhaust design

Postby philly » February 11th, 2014, 11:54 pm

philly wrote:Paul, i don know how much turbo technology youve worked on first hand, but do you think it would be a good idea to incorporate an anti reversion cone setup like the one described above with a turbo setup?

all else being equal i generally like to think of a turbo as a muffler, and although its easy to overcome poor turbo manifold/header designs with more boost, ive always wanted to build on the philosophy of being able to make a great set of tuned headers and channel them to a turbocharger. there has to be even more noticeable gain in this, turbo spooling faster, more responsiveness, quicker e/t's. of course one would have to calculate all the cfm figures for the intake and exhaust based on the amount of air the turbo is pushing into the cylinder.

would an easy way to find that number be multiplying the motors naturally aspirated displacement by the number of atmospheres (actual not gauge) that we would be forcing into the cylinder?


I just wanted to bring this back from the dead in the hopes that someone may have some insight. i see too many people hacking up and flipping manifolds around and all this nonsense as a form of convenience, and convenient tho it may be, there has to be power potential that people are missing out on.

thanks all
-phil

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