calculating header design

[grumpyvette]

YES THE SUB LINK INFO IS WELL WORTH READING ALSO
if your serious about maintaining good peak hp numbers use the calculators in the linked threads to actually calculate the ideal matched header dimensions, this is not a guessing game its strait physics and easily calculated to maximize exhaust scavenging and max volumetric efficiency, resulting in max power , at any given rpm and displacement, compression , cam timing etc this stuff can be calculated, but when dealing with an average and without knowing all the specifics you go by averages,and assume that peak hp takes a higher value than off idle torque
ok as a rule of thumb,when calculating and engines expected exhaust flow rates you can roughly assume 2.257 cfm per horsepower produced

if you have a 500hp engine it will in theory produce 500 x 2.257=1128.5 cfm of exhaust flow

or 141 cfm exhaust flow per cylinder, but your exhaust valve is only open about 220-290 degrees and the time between power strokes gets shorter as the rpms increase.
Of the 720 degrees in a complete engine cycle, theres lets say 250 degrees , or 250/720=1/3rd of the time, but it doesn,t all exit instantly so you can figure on about 1/2 the time the header primarys under significant pressure and pressure and pulse frequency varies with the rpms so the exhaust dump rates not at a constant flow or pressure, the header must handle 141 x 2=282cfm /115 =2.45 sq inches for exhaust flow per cubic inch , you look at the chart and find thats about a 1.7/8 diam. subtracting the pipe wall thickness






you will occasionally see dyno test results similar to this, that show about a 20 hp spread in the power curve, that seem to indicate that the difference in header configuration is not overly critical,but keep in mind these results are almost always done on 350-383 displacement engines with fairly mild compression , below 9.5:1 and fairly low duration cams ( example ,below 230 deg @.050 lift )and stock or mildly restricted exhaust systems, an engine with a fairly tight LSA and high compression and a low restriction or open exhaust can take full advantage of the headers scavenging the cylinders in a tuned rpm range significantly boosting the power produced, the tuned exhaust header has a greater effect on a higher compression ratio engine of larger displacement with a tighter LSA cam
you might want to read these also

viewtopic.php?f=56&t=185

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

PRIMARY PIPE DIAMETER FACTORS
The primary header pipe diameter is determined using basic engine mechanical specifications, such as: Bore Stroke Compression Ratio Valve diameter Cam specifications (lift and duration) Target rpm range

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

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

http://maxracesoftware.com/pipemax36xp2.htm

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

viewtopic.php?f=56&t=1730&p=4310#p4310

http://www.boyleworks.com/ta400/psp/exhaust3.html

http://www.autolounge.net/calculators/e ... izing.html

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

http://www.custom-car.us/exhaust/header.aspx

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

http://www.custom-car.us/exhaust/default.aspx

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

viewtopic.php?f=56&t=352

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

viewtopic.php?f=56&t=361

viewtopic.php?f=56&t=260&p=315#p315

viewtopic.php?f=52&t=796&p=1156&hilit=volumetric#p1156

http://www.carcraft.com/techarticles/03 ... index.html

http://autolounge.net/calculators/exhau ... izing.html

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

http://www.engineersedge.com/gauge.htm

How do you judge the i.d of a pipe?

3" o.d = 2.87" diam. inside
2.75 o.d = 2.62"diam. inside
2.5 o.d = 2.37" diam. inside
2.25 o.d = 2.12" diam. inside



theres THREE distinct areas of pressure/velocity
(1)
gases in the cylinders and header primary tubes as the exhaust exits the cylinders

(2)
gases in the header primary tubes and header primary tubes as the exhaust exits the header COLLECTORS

(3) the exhaust system past the collectors

(1) and (2) must be calculated to match the intended displacement ,cam timing and intended rpm range

(3) (traditional back pressure ) should be MINIMIZED


keep in mind installing an (X) almost increases the effective cross sectional area, of the dual exhaust ,or collector cross sectional area to double what it had been behind a single header collector, by doubling the area that the exhaust flow sees, dropping the restriction to flow almost in half

looking thru an (X) pipe





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

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


viewtopic.php?f=56&t=185

PRIMARY PIPE LENGTH
"The overall length of the primary header pipe is governed almost exclusively by the target engine's rpm range, and displacement which is dependent upon wave tuning. Typically, a lower engine rpm range likes a longer primary pipe, while a high rpm engine prefers a shorter primary."

SECONDARY PIPE DIAMETER (collector length in a 4 into one design)
While typical off-the-shelf street 4-into-1 headers do not have true secondary pipes, Burns' research has proven repeatedly that his Tri-Y designs make more overall power over a broader rpm range. While traditional lines of thought have street enthusiasts knowing Tri-Y pipes make more bottom-end torque, further research by Burns into the design have resulted in headers making more power all across the rpm range. With more components as part of the Tri-Y design, more tuning possibilities exist, and therefore more potential lives within.



"The secondary pipe diameter is determined by considering both pressure waves and reflective waves throughout the system. Since the pipes are paired according to the firing order, these waves can work together or against each other. Naturally, our designs work with the waves to increase the efficiency of the header, using the wave pulses to help pull gases from the engine.

"There are two basic kinds of waves we're dealing with. First, there are pressure waves. The pressure wave travels the length of the primary pipe in a 4-into-1 header, then is reflected from the collector where the area changes from the small-diameter primary into the larger-area collector. A reflection of negative pressure goes back up the primary pipe.

"In a Tri-Y design, the pressure of additional area changes (where the primary pipes become secondary pipes) produces additional reflections, so the Tri-Y must be designed in a different manner with respect to wave control. Given this, the area of the Tri-Y header between the first and second collectors becomes critical, and tuneable. The entire header is affected by this crucial length of pipe, and can be fine-tuned accordingly through proper sizing for optimal broad-range performance.

"The 4-into-1 pipe is also affected by altering pipe lengths, of course. But, without these secondary pipes it is impossible to tune with the same level of precision as with the Tri-Y headers. It's for this reason we prefer the Tri-Y design in most applications. The tuneability is so much more accurate, we're able to find more power over a broader rpm range. This is especially critical in engines expected to work well over a wide rpm range, like street machines."

Another huge reason for the move to Tri-Y headers is weight savings. Burn's claims most of their Tri-Y headers weigh in at about _ the weight of comparable 4-into-1 pipes for the same application, due to the smaller pipe diameters used throughout similar applications. Also, with less internal volume than comparable 4-into-1 headers, the Tri-Y equipped engine is typically more responsive. Tri-Y designs require physically smaller collectors as well, contributing further to space and fit concerns, and adding further to crisp engine responsiveness.

COLLECTORS
"There is much power to be found in researching collector design and size. The optimal collector is determined by several variables, and it's engineering interacts with the entire exhaust system. The internal volume, the outlet size diameter, and the angles at which the pipes come together within the collector are all factors that must be maximized for the header to perform to its full potential."

1 - Primary Pipe Entry Size
"Our computer model design program determines many of these hard dimensions based on data gathered over many years, including the length and diameter of the primary or secondary pipe entering the collector."

2- PRIMARY PIPE ENTRY ANGLE
"The pipe entry angle is typically between 10-20 degrees, with most pipes being right at 15 degrees. The cone (or goilet) formed between the pipes as they transition from primary to collector is formed as a consequence of these angles, nothing more. The mass of gases moving through the pipe does not want to change direction, so keeping these "pyramid" cones true to the pipe entry angle helps smooth the transition from the relatively small volume of the feed pipe to the larger volume of the collector."



3 - COLLECTOR OUTLET DIAMETER
"The collector outlet diameter is the most critical dimension in the header. It's what makes the merged collector work the way it does. Each collector we sell is custom-sized to each customer's engine, and there's no real 'formula' to get a broad-based general determination for street machines. As a rule, the overwhelming majority of aftermarket headers designed for the street market have way too big of a collector outlet diameter. Most street guys are losing power because of badly designed, manufactured, or engineered street headers. There is much room for improvement here."



4 - OVERALL COLLECTOR LENGTH
"Overall collector length is not critical. Once the other variables in the header design have been determined, the collector ends up being as long as it needs to be. We've found no benefit in lengthening or minimizing this dimension. It's more important to properly engineer what's going on inside the merged collector, and let the length determine itself once all the other important factors are optimized."



AFT OF THE COLLECTOR
One of the growing areas of research at Burns is the critical area just aft of the all-important collector outlet. Burns' dyno research led him to begin experimenting with interchangeable venturis, which slip into receivers just aft of the collector. While these prototype dyno parts were initially crafted to assist Jack in determining the critical overall collector diameter size, he soon realized they could be a marketable product. His initial "DynoSYS" product for dyno research evolved into a line of interchangeable sleeves called the Burns Tuneable Exhaust Collector, or BTEC for short.



The BTEC system has shown capability to alter the entire power curve of the engine. By changing only the insert, racers can change the entire tune on their engines to fine-tune for track conditions, weather, or driver preferences. Mostly used by drag racers, many in Pro Stock, the BTEC system offers enthusiasts a glimpse into the future of header design. While the drag racers have already embraced the benefits of BTEC, a number of road racers are beginning to experiment with the system as well.




X-PIPES
One area street machine enthusiasts are aware of is the evolution of the X-pipe. Early on, connecting the left and right halves of a true-dual exhaust system with an H-pipe resulted in measurable benefits. This theory evolved into the X-pipe, which allowed both left and right portions of the exhaust system to share some common flow area and resulted in even greater gains in power with a notable reduction in exhaust noise.


placing two x pipes in sequence seems to work well at both mellowing the exhaust note, and increasing the exhaust scavenging of the cylinders as it blends and smooths out the exhaust flow by allowing the individual cylinder pulse strength to dissipate rapidly, the first (x) reduces flow restriction, the second allows the exhaust pulse to run into itself further disrupting the individual pulse strength

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

http://www.engr.colostate.edu/~allan/fl ... /pipe.html


http://www.engr.colostate.edu/~allan/fl ... age7f.html




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



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

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

http://www.headerdesign.com/

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

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

http://www.porcupinepress.com/_bending/segmentbends.htm

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

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


http://racingarticles.com/blog/2008/02/ ... aders.html

[grumpyvette]

theres several good calculators and extensive info you can use in these links












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.pontiacstreetperformance.com ... aust3.html

http://www.popularhotrodding.com/tech/1 ... index.html

http://www.speedwaybids.com/forum/viewt ... 6e4152fd32

viewtopic.php?f=56&t=961&p=1654#p1654

don,t think your MAX rpm is what you use to compute, use the AVERAGE rpm durring a run

btw
http://www.cosworthvega.com/ExhaustFabII/Exhaust_Fab_II.html

http://www.chevelles.com/forums/showthread.php?t=165247&highlight=smurf

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

http://www.stahlheaders.com/Lit_measurement_1.htm

http://www.ssheaders.com/header.htm

http://www.engr.colostate.edu/~allan/fluids/page1/page1f.html

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

youll need this
http://www.kusashi.com/temperature.php?a=500&c=kels&d=fah&stage=results

http://stainlessheaders.com/

http://stainlessheaders.com/trans.htm

http://www.autoanything.com/exhausts-mufflers/65A2750A0A0.aspx

http://www.spdexhaust.com/

http://www.stans-headers.com/gm_flanges.htm

http://www.drgas.com/store/home.php

http://www.burnsstainless.com/

[grumpyvette]

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

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

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

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

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


http://www.spectrum5racing.com/Technica ... erRevA.pdf

your engines cam timing , compression ratio, displacement, rear gearing and average rpm , intake manifolds port design and cross sectional area, all effect the correct choice.
MOST GUYS BUY OFF THE SHELF HEADERS SO THERES NOT MUCH CHOICE,
... YOU INSTALL WHAT YOUVE BOUGHT AND LIVE WITH THE RESULTS,
but if your into building a true custom set of headers there ARE advantages to getting the size and length of the components correctly matched to the engine.
USE THE CALCULATORS

Ive found that if your header is designed too work peak efficiency at about 750-1000rpm under your red line youll generally be close to ideal on a street / strip combo.


lets say that 468 BBC runs in the 3500rpm-6200rpm band when racing, your cam, timing and compression ratio, matches and the intakes designed to that rpm band.
play with the calculators and for a street combo your probably going to want a header designed for both mid rpm tq and low high rpm restriction, a compromise of about a 2"-2.125" primairy about 36" long and a 3.5" collector about 18" long , seems about correct to maximize the mid rpm torque (remember the headers need to be fabricated from easily available components)

ON a 383 sbc, youll probably want a 1.75" about 38" long and a 3" collector about 19" long to maximize the mid rpm torque

[grumpyvette]

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

for you guys that refuse to read thru more than basic info links

BTW youll need your cam cards timing and/ maybe this chart, IF the advertised durration is all you have..

http://www.crower.com/misc/valve_timing_chart.html

EXAMPLE LETS ASSUME YOUR USEING A CROWER 01297 cam in a 496 displacement BBC and your trying for a max of 6000rpm
the cam timings given at .050 lift and we want the figures at about .004 so lets just assume we add 15 degrees to the timing and well be close enought to ballpark the exhaust size, needed.

http://www.crower.com/misc/cam_spec/cam ... &x=28&y=14

RESULTS

Your Primary Tube Length is 37.94
Your Primary Tube Diameter is 1.99 inches
Your Collector Length is 18.97 inches
Your Collector Diameter is 3.79 inches .

THAT WILL RESULT IN A HEADER THATS A DECENT COMPROMISE that provides a good power curve.

[grumpyvette]

http://www.hotrod.com/techarticles/engi ... index.html


http://hotrod.automotive.com/100121/hrd ... aders.html

BIG BLOCK HEADER TEST ON A 540 BBC

[grumpyvette]

http://www.circletrack.com/enginetech/c ... to_09.html

SBC HEADER TEST

[grumpyvette]

If you can,t find a decent quality header there are ways you can build a custom set-up, just a suggestion.........build a custom set exactly to the correct length for your application, with the correct collector.

you start by clamping the collectors where you want them after measuring to allow room for the correct primary tube length, and bolting the header flanges to the heads with the engine in the car, read thru the inks for ideas

theres readily available calculator info
theres pre-cut header flanges

http://www.summitracing.com/parts/HOK-11622HKR/

theres pre-welded collectors, its really not all that difficult

http://www.summitracing.com/parts/FLO-C134218234/

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


cutting your commercial headers short collector off and welding in a 4,2,1 extended collector is usually a good way to extend and increase the engines torque curve, but think it thru, theres the expense of the extended collectors, clearance issues and your welding and cutting and fabrication shills, I think the answer as to what course you take here depends on both your fabrication/welding measuring and cutting skills, experience and the quality of the headers your starting with, and your desire to try too maximize the engines power potential, I,m my experience theres no question, that if its done correctly youll make a bit more power, but it will also take some effort and might or might not be worth your time for the power youll gain.
now that might be anywhere from 15 hp to 50 more hp, dependent on the combo those headers are matched too.
and I don,t see the process of carefully fitting,the headers on the car, measuring and cutting the headers and cutting , trial fitting and welding the extended collectors several times (from experience) taking less than 4-6 hours, at 15hp that may be a waste of time in most guys way of looking at the time spent vs value gained, at 50hp i think most guys will see it as a good move, but you won,t know what youll get until your done testing, and in some cases clearances under the car make the modification and resulting under the car road clearance a total P.I.T.A., making you wish you were never involved so measure very carefully and don,t ignore the road to collector clearance issues!
http://www.summitracing.com/parts/DTC-80-01514C/


LINKS YOU'LL WANT TO READ

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

viewtopic.php?f=56&t=961

viewtopic.php?f=56&t=185

viewtopic.php?f=56&t=352

viewtopic.php?f=56&t=789

viewtopic.php?f=56&t=496

viewtopic.php?f=56&t=2870

viewtopic.php?f=60&t=1958

http://pitstopusa.com/i-5056669-schoenf ... chevy.html

viewtopic.php?f=60&t=72

watch this video,demonstrate, high speed air flow in adjacent primary tube sucks air flow thru next primary

http://www.youtube.com/watch?v=pDQXsfeZGwk

[grumpyvette]

gary posted this info, I think theres a few typos, in the math , but it looks interesting

"Ever wonder which is best 2.5 or 3 inch pipes? What about balance tubes? Is there a "right" place to put the muffler? Are tailpipes the hot ticket? And how do I choose or build the best header for my engine?

Get your calculator out, put your feet up, and start designing your own header and exhaust system, for your specific combo.With these exciting, ok, tedious, formulas straight from various engineering texts.

I use these for my stuff and have seen a 6 hp gain across the board and 10 at peak on a chassis dyno when replacing the best of the pre-bent X pipe stuff with a system designed like this....


1. First calculate individual cylinder volume.

(((Bore x 2.54) x (Bore x 2.54)) x (Stroke x 2.54) x 6.2832) / 8 = individual cylinder volume

2. Select desired peak horsepower rpm (i.e. 6000 RPM, from your dyno sheet if possible)

3. Identify exhaust valve opening BBDC (Before bottom dead center) in degrees (i.e. 67 degrees BBDC, from your cam spec sheet)

4. Calculate ED. Add 180 to BBDC spec (i.e. 180+67= 247)

5. Identify collector diameter inlet (almost always 4 inches)

6. Identify collector diameter outlet (almost always 3 inches)

7. Collector cotangent angle of taper will be 7 to 8 degrees for most headers

8. Calculate header primary tube length.

(ED x 850) / (Peak power RPM – 3) = primary tube length in inches.

9. Calculate primary tube inside diameter (ID)

Square root of ((Individual cylinder volume / ((Primary length + 3) x 25))) x 2.1 = primary ID in inches

10. Calculate collector length.

((Inlet diameter – outlet diameter) / 2)) x cotangent angle of taper = collector length in inches.

11. Calculate intermediate (collector to muffler)pipe ID

Square root of ((Individual cylinder volume x 2)/((Primary tube length + 3) x 25)) x 2 = pipe ID from end of collector taper to front of muffler

12. Calculate intermediate pipe length

(Primary tube length+3)-collector length = intermediate pipe length in inches

13. Calculate balance tube ID

1.5 x Primary tube ID = balance tube ID in inches

14. Tailpipe. Same ID as Intermediate. Minimum 8 (12 is better) inches long to scavenge the muffler. It can be any length as long as it’s not shorter than 8 inches.

The header you just designed will ensure that the sonic reversion pulse travels back up the pipe to the exhaust valve precisely at the right time at peak power RPM. The exhaust system will support the pulse timing and scavenge the header and muffler. See, it's simple..."

[grumpyvette]

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



knowing a few constants in engine pressure and flow helps

an engine usually requires approximately 2.257 cubic feet per minute per horsepower to maximize intake flow and exhaust flow at about 115 cfm per square inch, that holds basically constant wither your spinning a 302 to 7800-8000rpm with 4000fpm in piston speed or a 406 to 6000- 6200rpmrpm

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 2.257 cfm and you see you need 565 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).

as a cross check 500hp /8=1129/8=142 hp per header primary , 2.257 x 142/115=2.76 sq inches 0r a header primary a bit larger than 1 3/4 and smaller than 2" or a 1 7/8 to maximize peak hp, per header primary, but keep in mind you'll spend most of your time below peak rpms so a slightly smaller 1 3/4" primary on a street strip engine that sacrifices a bit of peak hp for better mid rpm torque makes sense, and once you install longer exhaust pipes and mufflers you'll need to steep up the exhaust pipe size cross section past the header collectors or they will tend to be restrictive at the minimum size the formula predicts
at any given rpm and displacement, compression etc this stuff can be calculated, but when dealing with an average and without knowing all the specifics you go by averages,and assume that peak hp takes a higher value than off idle torque
ok as a rule of thumb,when calculating and engines expected exhaust flow rates you can roughly assume 2.257 cfm per horsepower produced

if you have a 500hp engine it will in theory produce 500 x 2.257=1128.5 cfm of exhaust flow

or 141 cfm exhaust flow per cylinder, but your exhaust valve is only open about 220-290 degrees and the time between power strokes gets shorter as the rpms increase.
Of the 720 degrees in a complete engine cycle, theres lets say 250 degrees , or 250/720=1/3rd of the time, but it doesn,t all exit instantly so you can figure on about 1/2 the time the header primarys under significant pressure and pressure and pulse frequency varies with the rpms so the exhaust dump rates not at a constant flow or pressure, the header must handle 141 x 2=282cfm /115 =2.45 sq inches for exhaust flow per cubic inch , you look at the chart and find thats about a 1.7/8 diam. subtracting the pipe wall thickness

you might want to read these also

viewtopic.php?f=56&t=185

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

viewtopic.php?f=56&t=1730&p=5392#p5392

viewtopic.php?f=56&t=495

viewtopic.php?f=56&t=1503


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

[grumpyvette]

HERES RELATED INFO THAT WAS POSTED ELSE WARE
It ain't just pipes, it's science! Part 1

I’d like to try to explain some basic exhaust theory and clear up some
issues that may not be completely clear.

Everyone knows the purpose of an exhaust system is to provide a means for
the exhaust gases to be removed from the cylinder. You might wonder why
have an exhaust system at all. Other than the frequent need to muffle the
noise of rapid combustion, why not simply open the exhaust port to the
atmosphere, thereby saving both weight and expense?

Some time back in early internal combustion engine history, it was
discovered that attaching a length of pipe to the exhaust port (probably
to direct the noxious exhaust fumes away from a passenger compartment or
out of a room where a stationary engine was housed) often had an effect on
the performance of that engine. Depending on parameters such as pipe
diameter and length, the performance could be adversely or positively
impacted.

I expect it was clear from the very beginning that exhaust gases have
momentum. What may not have been known at the outset is that they also
exhibit wave properties, specifically those of sound. Both those
properties can be utilized to evacuate the exhaust gases more quickly and
completely. The usual term for this removal process is “scavenging.”

There are two types of scavenging: inertial and wave. Inertial
scavenging works like an aspirator whereby some of the kinetic energy of a
moving fluid stream (air, water, etc, generally in a pipe) is transferred
to the fluid in an adjacent pipe. You may remember from high school
chemistry lab class where you used water traveling through the top of a
“T” fixture to draw a quite powerful vacuum in an attached vessel.

The “T” can be likened to a merge collector as used in virtually all
successful racing cars (although often not in dragsters). The most
effective merge collectors minimize the volume increase at the juncture of
the pipes. If this volume is too large, gas speed is diminished and less
kinetic energy is transferred to the gases in an adjacent pipe. Thus, the
scavenging is less complete. Well, so what if there is a little gas left
in the pipes? Consider the engine cylinder as an extension of the exhaust
pipe. A cylinder with residual exhaust gases has less room available to
accommodate the incoming charge of gas and oxygen. Obviously, the more
gas and air you can get into a cylinder, the more power is developed; that
is why superchargers are so effective.

Not only can scavenging be utilized to empty the cylinders, it also can
help to draw in the new charge, by producing a negative pressure in the
cylinder. This gets tricky because there has to be adequate time in which
both the intake and exhaust valves are open, and there is the potential
problem of the new charge passing right through the cylinder into the
exhaust pipe! Gas is wasted and power is lost. Maybe you can design your
cam such that it closes at just the right time to prevent this from
occurring. Or maybe you can make the exhaust pipes just the right length
so that the reflected sound waves (at a particular engine speed) prevent
the incoming fuel and air from spilling out of the cylinder. More on this
later.

A stock S4 engine has very little valve overlap (some at small valve
openings) and therefore there is only a short time during which scavenging
of the cylinder can be accomplished. Even still, there is opportunity for
significant performance gains with effective scavenging of the primary
exhaust pipes (the first pipes that emanate from the ports) where it’s
possible to produce a negative pressure so that when the exhaust valve
opens, exit speed is increased. The result is increased momentum and
possibly improved cylinder evacuation.

On to wave scavenging. An analogy would be tuned organ pipes in which
their length is adjusted such that a standing wave of a particular desired
length (and frequency) is established. This means that some whole number
of waves will fit exactly within the length of the particular pipe. When
the point of maximum amplitude of a wave comes to the end of the pipe or a
change in diameter, the wave is reflected back up the pipe, but as its
mirror image. Thus a positive pressure wave is reflected as a negative
pressure, or rarefaction, wave which, in turn, helps to draw spent gases
from the pipe/cylinder. Wave scavenging is most effective over a narrow
speed range that can be adjusted by changing the primary pipe length.
Thus a torque or power peak can be designed to occur at a particular
engine speed to suit the application whether it is racing or everyday
driving.

What are crossover headers? There are numerous types of headers, tri-Y,
equal length, stepped, unequal length, crossover, etc. Unequal length
headers are by definition not tuned at a specific rpm; rather each pipe is
tuned for a different speed. They tend to perform better than the stock
manifold and may increase performance over a broad speed range. Because
of their unequal length, each pipe will utilize wave scavenging at a
different speed, thus reducing the effect at any single or narrow band of
speeds. They often have sub-optimal merge collectors and so, do not make
the best use of inertial scavenging. Equal length headers can be
excellent wave scavengers, but often have inferior collectors, so inertial
scavenging is not optimized. The tri-Y design is especially good on
4-cylinder engines and is now being used almost exclusively on NASCAR
engines with 8 cylinders. Stepped headers gradually increase the pipe
diameter going away from the port. I believe at least one of the purposes
is to inexpensively approximate a megaphone which is the most efficient
device for returning the pressurized gases back to the surrounding
atmosphere. "

[Indycars]

On to wave scavenging. An analogy would be tuned organ pipes in which
their length is adjusted such that a standing wave of a particular desired
length (and frequency) is established. This means that some whole number
of waves will fit exactly within the length of the particular pipe. When
the point of maximum amplitude of a wave comes to the end of the pipe or a
change in diameter, the wave is reflected back up the pipe, but as its
mirror image. Thus a positive pressure wave is reflected as a negative
pressure, or rarefaction, wave which, in turn, helps to draw spent gases
from the pipe/cylinder. Wave scavenging is most effective over a narrow
speed range that can be adjusted by changing the primary pipe length.
Thus a torque or power peak can be designed to occur at a particular
engine speed to suit the application whether it is racing or everyday
driving.

I noticed when CCing the combustion chambers that I could see the reflected wave coming back when the wave hit the other
side of the chamber. It would easier to see this in a pan of water while using an eye dropper, you do have to look
closely or you will never notice what's happening.

Or you can watch this video. Take close notice at the 2:08 min:sec mark in the video.
http://www.youtube.com/watch?v=zyqCgtvMwfw

[grumpyvette]

http://www.popularhotrodding.com/tech/1 ... index.html


How To Size Headers Pipe Sizing Chart
How To Size Headers
This chart works well for high-performance heads in as-cast or ported form. To determine the primary inside diameter, you will need a good ballpark figure for the exhaust flow at the peak valve lift. Using this figure, go up the chart until you reach one of the colored lines (green for street, purple for street/strip, blue for race). At that point go across the chart and read off the pipe ID required.





How To Size Headers
Here are some dyno test results of four different primary tube lengths on an 8.5:1 compression 350 Chevy. The shortest length at 18 inches (black curves) show the engine did not like really short primaries. But the 29-inch (green), the 32-inch (red) and the 38-inch (blue) headers all performed well with only a moderate bias toward better low end from the longer pipes.



Here we see the effect of adding a tuned length (about 12 extra inches) to the normal stub length seen on a regular collector. The addition of 12 hp and 10 lb-ft is good, but just check out the 40 lb-ft gain at 3,600 rpm.

[grumpyvette]

I was wondering if anyone has played with collector extensions on your headers. I had an interesting thing happen this past weekend. When I went to the 2" Doug's a little over a year ago I also had some 10" x 3 1/2" extensions fab'd up. It's just an old school thing I used to run way back in the day (plus I like the sound).

Well I finally decided to take them off and see what if anything would happen. Next pass the car immediately lost 1 1/2 MPH (ET was close but down maybe 2-4 hun). Next pass I put them back on and the MPH came right back..no other changes to the car, tune, launch, weather...nothing....MPH stayed at its normal number the rest of the day.

Just thought it was a curious thing, maybe I just happen to hit on something these headers like with the extensions....anyone have any experience with this?? thx, Davey

this can and does change a great deal with each combo but its not all that rare to find that a 14"-24" collector extension, added to the headers collector helps cylinder scavenging efficiency, Ive repeatedly found similar gains, while tuning cars and I,m always amazed at the guys that slap headers on a car and think thats all thats required to get the engine to perform to its max potential.
theres calculator programs that will help predict the best combo but they rarely give you the exact info, it usually takes some actual track time and tuning to find the best combo in the real world.
Ive generally found most collectors are too large in diameter to produce the best results, and if you calculate the cross sectional area of TWO primary pipes and install a collector just a bit larger in cross sectional area you get better results


look at the chart, as an example if your header primary is 1.75" its got 2.4 square inches so twice that area is , nearly 5 square inches, a 2.5" diam collector is very close, but you generally select the next size up so 3" diameter collector extension near 18" long would be where Id suggest starting on a header collector extension, and if you can run the header collectors into an (X) pipe in many cases it helps scavenging efficiency even further

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[grumpyvette]

http://www.popularhotrodding.com/tech/1 ... dyno_test/
I can,t begin to tell you how many times Ive seen the "FACT" that 1 5/8" headers will produce more torque than the larger 1 3/4" headers
or similar info posted, the TRUTH is that each cam, engine displacement and combo of components will effect your results and only testing and a bit of experimentation with collectors and cam timing , ignition timing a bit differently can change the results

THE HORSEPOWER NUMBERS and a test of big block chevy engine testing with different headers
RPM Shorty 1¾ 1⅞ 2.00 2⅛
3,000 255.0 261.7 266.7 262.8 271.0
3,100 263.5 270.5 276.5 272.6 280.3
3,200 274.0 282.3 287.8 284.8 291.7
3,300 286.0 296.1 300.4 298.2 304.2
3,400 298.3 310.6 313.6 311.5 316.6
3,500 309.3 324.9 326.3 323.7 328.5
3,600 320.1 338.6 339.2 335.7 339.7
3,700 331.3 352.8 352.2 348.6 350.6
3,800 342.7 367.0 364.2 362.2 361.3
3,900 354.4 379.6 374.6 375.4 370.8
4,000 366.3 391.1 384.5 387.1 379.7
4,100 379.5 402.1 395.5 398.2 388.9
4,200 394.3 413.0 408.0 409.3 399.1
4,300 410.0 424.2 421.1 420.3 410.4
4,400 425.5 434.9 434.2 431.7 422.9
4,500 439.4 445.4 447.4 444.1 436.3
4,600 451.6 456.1 460.9 457.5 450.3
4,700 462.6 467.4 474.7 470.7 465.7
4,800 473.3 478.7 488.9 483.8 479.9
4,900 483.1 489.3 501.6 496.6 492.9
5,000 492.3 499.0 512.5 509.0 505.2
5,100 501.2 507.9 522.2 520.8 517.0
5,200 510.0 516.0 531.1 531.6 527.7
5,300 517.9 523.7 539.5 541.0. 537.8
5,400 524.7 530.9 547.3 549.1 547.0
5,500 530.0 536.8 554.3 556.5 554.5
5,600 534.4 541.8 560.4 562.9 561.0
5,700 537.9 546.0 565.8 568.3 566.5
5,800 540.7 550.1 570.2 572.3 571.3
5,900 543.4 553.8 574.0 576.3 576.4
6,000 546.5 556.7 577.0 581.2 580.5
6,100 549.4 559.0 579.0 585.4 584.3
6,200 551.6 560.8 581.2 588.8 587.4
6,300 554.1 561.3 582.2 591.1 589.1
6,400 554.4 560.5 582.4 592.6 589.3
6,500 552.9 558.5 581.0 592.3 589.2
6,600 549.0 554.7 577.7 590.8 587.1
6,700 540.5 550.4 573.3 586.9 583.2

[philly]

vef1.jpg

grumpy, can we infer from this diagram that making exhaust primary and intake runner lengths for different rpms we broaden our powerband? maybe lose some peak hp but possibly pick up plenty of average tq?

[grumpyvette]

Ive always tried to get the engines compression, cam timing, displacement, intake runner tuning and exhaust scavenging to fall as close as I can in the rpm band, so i can select the converter stall and rear gear ratio to maximize that peak from the torque peak to and a bit past the power peak, deliberately screwing that power curve up to broaden and lower the power produced never entered my mind, now Im sure I screwed it up a bit at times and had some parts operating a bit more effectively that other parts at some point in the rpm band but it was never intentionally done, simply because done correctly theres still a fairly wide and useful 1500rpm-3000rpm power band you gear the car for

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