calculate the ideal exhaust pipe diam. for your application

[grumpyvette]

IF YOU DON,T TAKE THE TIME AND EFFORT TO READ THRU THE LINKS WITH A GOOD DEAL OF USEFUL INFO, YOUR NOT GOING TO LEARN ALL THE FACTS,NECESSARY TO MAKE INTELLIGENT CHOICES



http://www.mk5cortinaestate.co.uk/calculator5.php

http://www.veryuseful.com/mustang/tech/ ... enging.pdf

http://www.wallaceracing.com/header_length.php

http://www.bgsoflex.com/bestheader.html

http://www.superchevy.com/technical/eng ... index.html

http://www.carcraft.com/techarticles/he ... usion.html

http://www.centuryperformance.com/exhau ... g-137.html

http://2.3liter.com/Calc2.htm

http://www.chevyhiperformance.com/tech/ ... index.html

http://www.antechlabs.com/K0GFM/pipechart.gif

http://www.fabshopheaders.com/header-sizing.html

http://www.wallaceracing.com/header_length.php

http://www.bgsoflex.com/auto.html

http://www.antechlabs.com/K0GFM/pipechart.gif

http://dairally.net/daihard/chas/MiscCa ... iPipes.htm

viewtopic.php?f=56&t=260

viewtopic.php?f=79&t=407&p=5393#p5393

viewtopic.php?f=56&t=1166

http://www.pontiacstreetperformance.com ... haust.html

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viewtopic.php?f=56&t=1303

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http://www.enginedesigner.com/Engine_Designer_Docs.html

You'll want to keep in mind that there's two totally different routes to take here and it does matter in your choices, selected
if your designing an exhaust system there's compromises to be made
if your not running headers you'll want to balance the exhaust pipe diam. selected, so you get a large enough inside diam. to not be to restrictive , yet it needs to be small enough to maintain high enough exhaust gas velocity , that it tends to drag following exhaust pulses along with its as it exits the car/truck, obviously exhaust length, engine displacement and rpms will play a huge role in the calculations., in effect the exhaust pipe is acting as both primary and collector so it will tend to favor the low and mid rpm ranges, if its small enought to enhance low rpm torque , like most factory exhaust systems are designed to do,simply because as rpms increase the flow increases, since the exhaust diam. stays constant the pressure and volume will tend to increase, and at some point get restrictive
If you have headers the primary tube length and diam. , and collector length should ideally match the engines intended effective power band, but the exhaust pipe diam.past the collectors (which in combination with the primaries are providing the cylinder scavenging) needs to be as low in restriction too flow as you can fit under the car with noise and clearance issues taken into concern, during the selection process.

well worth reading

http://www.popularhotrodding.com/engine ... ndex1.html

the more mysterious and difficult they can make the process of intake and head porting appear, the more likely you'll think you can,t do the work, and you'll pay to get it done, it helps a great deal to understand what your doing and why and how its done but almost anyone with some research can make basic improvements that help the hp curve, you may not get the full potential a guy with experience and a flow bench could get but you can make noticeable gains, look the object is to increase VOLUMETRIC efficiency (big complicated term for effectively filling the cylinder at higher rpms), almost anything you can do to lower flow restriction without reducing port speed on the intake runners noticeably helps) but remember what goes in MUST exit also to allow the next charge to enter the cylinder so effective exhaust scavaging of the cylinders and cam timing will play a big part in the intake flow rates or lack of flow

http://forum.grumpysperformance.com/viewtopic.php?f=52&t=462&p=2833#p2833

http://forum.grumpysperformance.com/viewtopic.php?f=52&t=1740

http://forum.grumpysperformance.com/viewtopic.php?f=52&t=333

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=260

most exhaust pipe is 16 gauge, or .065 wall thickness

http://www.engineersedge.com/gauge.htm
Engine Size
Horsepower
Exhaust Diameter
Single Exhaust
Dual Exhaust
150-200 CID 100 to 150 2″ to 2-1/4″ 2″
200-250 CID 100 to 200 2-1/4″ to 2-1/2″ 2″ to 2-1/4″
250-300 CID 150 to 250 2-1/2″ to 3″ 2″ to 2-1/2″
300-350 CID 200 to 350 2-1/2″ to 3″ 2-1/4″ to 2-1/2″
350-400 CID 250 to 550 3″ to 4″ 2-1/2″ to 3″
How do you judge the i.d of a pipe?

3" o.d = 2.87" diam. inside--approximately 6.5 sq inches of area
2.75 o.d = 2.62"diam. inside--approximately 5.4 sq inches of area
2.5 o.d = 2.37" diam. inside--approximately 4.4 sq inches of area
2.25 o.d = 2.12" diam. inside--approximately 3.5 sq inches of area

knowing a few constants in engine pressure and flow helps

an engine usually requires approximately 2.25 cubic feet per minute per horsepower to maximize intake flow and exhaust flow starts to become restrictive at about 115 cfm per square inch


its a rule of thumb or rough guide on the expected combined potential max exhaust port flow rates of the exhaust taken from an observed average of hundreds of recorded dyno results, and not taking into account any flow loss or restriction,and calculating some heat expansion ,its basically worthless except as a way to figuring what size exhaust pipe size thats likely to work, or what size will be restrictive to flow.


viewtopic.php?f=52&t=322

so assuming your building a 500 hp engine / 2 (divided by 2 as there's normally two header collectors on a v8) we have 250hp per header collector, (open header collectors) multiply that by 2.25 cfm and you see you need 562 cfm and divide that by 115/square inches and we see we need a 4.9 square inch minimum exhaust collector pipe, per side (open header collectors).

UNLESS you match ANY header with a TRUE low restriction exhaust its can NOT possibly work to NEAR its FULL potential, headers are designed to SCAVENGE the cylinders of oil burnt exhaust gases and INCREASE the percentage of fresh fuel air mix, if theres any significant back pressure beyond the header collectors that cuts the headers efficiency way down





http://forum.grumpysperformance.com/viewtopic.php?f=56&t=495

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=3155

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=1503

 

[sean g]

just a note, for turbo applications this information is not very useful. the turbo itself (in most cases) provides more backpressure than ever needed, and power will be determined by the pressure differential over the turbine, i.e. larger outlet piping than inlet piping.

 

[grumpyvette]

Re: calculate the ideal exhaust pipe diam. for your applicat

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 scavenging 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

http://www.carcraft.com/howto/ccrp_0803 ... index.html

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 scavenging but that's not always possible due to clearance, and if you choose to place an (H) just before the mufflers its mostly to reduce resonance or noise not increase scavenging but it tends to reduce the restriction to flow

http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=50

"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 diam. and length it usually does help the cylinder scavenging a bit more than one alone, but again the closer to the exhaust headers the better off you'll 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 bell housing 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 primary diam. and length and the collector design are what effects the cylinder scavenging , 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 diam. 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 originating 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 scavenging and there length and dimensions are calculated to maximize that scavenging effect the exhaust past the collectors is basically designed for noise abatement and safely exiting the exhaust gases.
you get very little scavenging 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

 

[guysmontess]

Do you have any back to back dyno tests comparing a car equipped with a 2.5 inch exhaust pipe versus a 3 inch exhaust pipe,with every thing else being equal ???
I am curious to see real world results in this area.
Guy

 

[grumpyvette]

Re: calculate the ideal exhaust pipe diam. for your applicat

viewtopic.php?f=79&t=497

viewtopic.php?f=56&t=495

read thru ALL the sub linked info in this thread, and ITS SUB LINKED THREADS
its not at all rare for a swap from 2.5"-to-3" exhaust on a sbc or mild bbc or from 3"-to-3.5" on a radical big block to add 5-15hp, depending on the restriction that was removed behind the collectors or exhaust manifolds, back pressure reduces the effectiveness of the exhaust cylinder scavenging, and once you tune the engine to take full advantage of that reduced restriction and better cylinder scavenging factor you get the full benefits that the reduced back pressure tends to provide.
keep in mind the lower rpm TORQUE LOSS that's occasionally reported is FREQUENTLY a tuning issue as the more effective scavenging tends to lean out the effective fuel/air ratio, and any curves or mufflers on the exhaust system tends to restrict and reduce exhaust flow forcing you to step up the pipe cross sectional area to maintain the necessary low restriction rates to maximize hp in any exhaust bolted on past the header collectors if you intend to maximize the engines peak hp/tq

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

http://www.stahlheaders.com/docs/2006catalog.PDF

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

knowing a few constants in engine pressure and flow helps

an engine usually requires approximately 2.25 cubic feet per minute per horsepower to maximize intake flow and exhaust flow starts to become restrictive at about 115 cfm per square inch


its a rule of thumb or rough guide on the expected combined potential max exhaust port flow rates of the exhaust taken from an observed average of hundreds of recorded dyno results, and not taking into account any flow loss or restriction,and calculating some heat expansion ,its basically worthless except as a way to figuring what size exhaust pipe size thats likely to work, or what size will be restrictive to flow.


viewtopic.php?f=52&t=322

so assuming your building a 500 hp engine / 2 (divided by 2 as there's normally two header collectors on a v8) we have 250hp per header collector, (open header collectors) multiply that by 2.25 cfm and you see you need 562 cfm and divide that by 115/square inches and we see we need a 4.9 square inch minimum exhaust collector pipe, per side (open header collectors).




you can also use intake port flow as a rule of thumb, ie number of cylinders x max port flow art max cam lift x .257 = max theoretical hp an engines likely to produce, before the heads and intake become a restriction

IE if a vortec head 350 flows 229 cfm at .600 lift and your spinning the engine fast enough too maximize the port flow rates,so in an ideal world you can expect 229 cfm x.257 x 8 cylinder =470hp before the heads become a restriction if everything else is perfectly tuned

viewtopic.php?f=52&t=322


the question often comes up about use of mandrel bends vs crimp bent exhaust pipes, in designing an exhaust system, well it should be noted that its the cross sectional area much more than the shape of the pipe thats the more important factor, while its true that mandrel bends do maintain a more consistent cross sectional area, simply selecting a slightly larger diameter non-mandrel bent exhaust pipe size with its larger cross section can frequently be the less expensive route. as long as you've got an (X) pipe in the system , mounted as close as clearances under the car allow, to the header collectors and the tail pipes are nominally the same diameter, as the formulas suggest are required, IE lets say 2.5" or 3" the type of bend at that point, (past the (X) PIPE, will be all but meaningless due to the fact that by that point the exhaust pulse strength and velocity has been significantly reduced thru cooling distance, the effect of the (X) pipe splitting the pulse,and the lack of significant restriction.
every test Ive ever seen shows that an (x) pipe mounted near the header collectors and mandrel bends on collectors do help flow, but youve effectively almost doubled the cross sectional area after the (x)and because the engine fires every 90 degrees the pulse of exhaust past the (x) is significantly reduced in exhaust pressure, your exhaust will normally require an exhaust pipe that will handle the flow based on the engines air flow rate and horse power
you can use the info posted

 

[grumpyvette]

Re: calculate the ideal exhaust pipe diam. for your applicat

like most things EXPERIENCE HELPS, when your designing an exhaust system for your car, but if you mock up whats needed its not going to be difficult to do.
generally you carefully measure, the length and angles and buy a few pipes to cut and weld and use a pipe expander, after doing the required calculations, the links below will help you do that .

to make one end female so you can slip the normal pipe inside a slip fit giving you some leway on exact length.

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