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Old 08-31-2006, 01:50 AM   #1
Back Road Runner
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Default Everything you ever wanted to know about exaust systems

I stumbled across this article discussiong exaust systems, very nice read :
http://www.superchevy.com/technical/...exh/index.html

It got me making up a few tables in Excel and getting an idea of tuning. Now I'm wondering if a local exaust shop could fabricate a built-to-spec system for cheap...
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Old 08-31-2006, 03:52 PM   #2
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Another article I ran across, similar info, more geared towards headers only:
http://www.carcraft.com/techarticles/header_basics/

Header diameter somes out quite close to the other link above. It seems the optimum velocity for scavenging is 240 feet per second (fps) and is based off the desired torque peak rpm and will define our header diameter.

I still haven't found anyone specifically mention header length. However, is seems quite varying. We're tuning sound waves in an environment that varies greatly in temperate and thus speed of sound. We'd have to know the operating temperatures of the exaust gases. I've only found a couple references, 1300 Celcius for race applications and 720 C from an article discussing aircraft engines.

For tuning length, I think it's less of a matter of headers alone but rather header + secondary till we hit an area of pressure loss like a resonator, or muffler, may add to secondary length(glass pack). Other than longer = lower rpm torque, higher = higher rpm torque, I'm not really sure how to accurately approach this.

The rest of the system seems easy enough. Use a pipe and muffler of high enough flow to not restrict. Keep as small as possible(without restriction) to keep things decently quiet. I guess we could use the 2.2cfm x max open exaust HP or pipe diameter-flow rate relations and pick accordingly off cfm @ max rpm.

One additional thing I'm not sure about is resonators. I can see them used for defining the end point of the secondary piping, to define header + secondary and ultimate wave tuning. However, I'm not sure how big it should be. How big is enough to sufficiently define an end reflection point. How big can one go? Is there such a thing as too big? How does it affect the end exaust note. Bigger of course means quieter and I assume a lower note, but I'm not sure about ultimate tuning. As well, should it be tuned against/with the engine's frequency?

Our car cruising at highway speed at 3000rpm will resonate at 100Hz or exhaust spent gases 100 times during a 1 second period. (3000rpm -> 50rps -> 25 exhaust strokes per cylinder * 4 cylinders -> 100 exhaust strokes per second ) Can we tune the resonator to cancel out any freeway drones, or can we use it to tune in a specific note?

I'd like to leave this thread as an open discussion, really work out the details and maybe nail down some specifics. It would be neat to translate some current exaust offerings from some of the major companies to get an idea of how they tuned their systems and what they may be geared for.

A touch off topic but along the same principles. I assume the intake works in exactly the same way and also requires tuning. You have the intake headers, a single collector point(throttle body), a resonator/secondary terminator in the form of the "magical" airbox, and the remainder of the intake tracking. We have some different goals, but it seems all the principles work the same. It also shows why the stock air box functions so well. No one else takes into account to function of the box. It also shows why people have seen gains from throttle body spacers(which nobody seems to make anymore). It acts as a secondary extender, shifting torque gain lower.

This is pretty neat stuff that can be applied to both sides of the engine.

Also, this book seems to be a suggested read for anyone interested in exhaust design:
"Scientific Design of Exhaust and Intake Systems"
by Philip Hubert Smith, John C. Morrison
http://btobsearch.barnesandnoble.com...37603099&itm=1
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Old 08-31-2006, 08:23 PM   #3
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Came across a second iteration of the initial article.

It seems the Resonator should be at least 8 to 15 times the volume as the displacement of one cylinder.

Well, that answers one question.
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Old 10-04-2006, 08:21 PM   #4
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Never mind about the resonator thing. It's a muffler...in the simplest form. You can use it to tune/quiet the exhaust note or do something like end the scondary tuning...

Anywho, came across a little piping calculator, thought it was interesting:
http://www.btinternet.com/~mezportin...st_length.html
(weee, length numbers )
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Old 10-04-2006, 08:47 PM   #5
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Check www.headerdesign.com too. You have to register with them to use their header design calculator, but I haven't seen any signs of spam overload as a result so I think it's safe. Pretty fun to play with.

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Old 10-04-2006, 10:03 PM   #6
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I'll give it a look.

My biggest question is proper lengths. It's all timing. You have diameter to control the speed, but you need the length to optimize the pulses. The articles I've found so far aren't real specific on length. Of course, it's a finicy thing as it's all controlled by temp.
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Old 10-05-2006, 12:21 AM   #7
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Hmm, they certain are exacting

The odd part is unless you actually make your own headers, you won't find anything near these numbers. All the aftermarket options available seem pretty far off.

Made a little table in Excel of the results...just seems a little too exact. A note on the Tune, you're basically picking where you want your power band. 1 is basically at half peak power, i.e. street, economical, low end power. 4 starts to get into the performance level, improved top end, etc. 7 and up are more hardcore, sort of race specific, lots of focus on top end power. It's basically their scale, 1 to 10.

Now, you may notice the numbers are pretty close to each other, not much for major changes. You're looking at 1 or maybe 2 pipe size changes(in 1/8" increments) and lengths varying in a few inches...from mild daily driver to hardcore race trim.



Still, the site's nice, offers a lot of good info. I would assume the data is actually quite good, perhaps too good? I guess if you worried about this at a professional level, you may look at this down to an inch or two, but I can't see it being practical in the real world. Interesting enough, it makes all the aftermarket solutions for our cars look like they're geared for all out race performance. Cobb/OBX/Rallitek and TWE use 1.65" diameter piping of some length, 2.25" collector of some short length, and you're running 2.25" pipe all the way through(unless you want to change diameter). Borla steps further and runs a slightly larger header pipe diameter(1.7") but a smaller collector(2"), and very uneven lengths. Some of the other common data I've found more closely supports the numbers being used by the above manufacturers.

Working throw a generic optimum flow rate of 240fps for scavenging, assuming a wide scavenging range of 4000rpm, and picking a middlerange 4500rpm peak tuning point(looking for 2500-6500rpm effect), I get an optimum header pipe diameter of around 1.65" and a secondary/exhaust of 2" to 2.25" to support flow up to redline(115cfm/in^2, 2.2cfm*HP), pretty much the same numbers all the manufacturers are using.

I don't know.

Last edited by Back Road Runner; 11-10-2007 at 03:06 PM.
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Old 10-07-2006, 02:29 AM   #8
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Hmm....curious...
https://www.headersbyed.com/index.htm


...and they're relatively local to me.
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Old 10-07-2006, 03:16 PM   #9
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I'm going to fill out a questionaire for them...see what I get for options. If their pricing's good, I may end up with something from them. We'll see.

I have my own focus, so I'm looking for wide band usability with just good power everywhere, 2000-6500rpm, and only an entry level of bolt on upgrades like intake, full exhaust, ECU flash, lightweight flywheel/pulley, things like that.

I'm quite curious what they suggest for design and where it stands compared to the info I've found so far.

It costs $40, but that does fully go towards credit on the purchase of a header or partially for header parts, not really losing out unless it's just advice service. Of course, knowledge from the pros isn't bad either.

I'll keep you guys posted.
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Old 10-24-2006, 09:59 PM   #10
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Just an update. I got what I guess I could call an informational packet back from Headers By Ed after filling out their questionare.

He suggests some specific values for my desired setup. I asked for a design that was geared for midrange power and gave a usage range between 2000rpm to 6500rpm. I noted 6500rpm would be seen during any "racing," and that gas milage was important, i.e. good and peak torque around 3000rpm. i gave note that I'd be running two Car Sound high flow cats and a Borla XS muffler.

My solution:
Header:
- 1.5" diameter
- 36" total length
Collector:
- 2.25"
Exhaust:
- 2.25" all the way through

*diameters are outside diameters

Some key notes, suitable primary diameters of 1.5" and 1.625" were the only acceptable options for this application. Smaller would be restrictive and larger would be detrimental to low and midrange power and could only be used by a race built engine.

The primary length was given at 36" minimum. Shorter would lose low and mid range power. If anything only go longer if 36" was unachievable. It's better to have excess length than too short of a primary.

Collector size was discussed. A smaller diameter provides better low and midrange power. It shouldn't be too short or too long(given an open exhaust design). In a mufflered setup, the system kind of ruins the purpose of the secondary but a foot or so length of straight piping should be devoted to the secondary before there should be any curves.

He mentioned that a 2" exhaust would yeild better low and mid range power, but it could potentially limit flow at higher rpms. Milage would also improve under normal driving.

The informational packet was basically packed with about 40 years experience with building headers for auto manufacturers, racers, and enthusiasts. He coverd several key points for getting the most out of setup and just general do's and don'ts. I won't really cover anything in detail.

The packet also comes with a parts catelog. Unfortunately, modern cars are not his domain. There are premade kits for older domestic models. For work like mine, his service is simply more as a construction guide, an advice service if you will, as well as a resource for getting quality hardware to build your own. You can order raw materials for the build, mandrel bent piping of various diameters and radii, collectors, and it seems that you can have the header flanges custom built for you car given a sketch of the exhaust port. He can build a quality flange and can even include an initial pipe section to start any custom work(potentially benificial if the port shape is goofy). However, a full header build is...extensive to say the least. He limits himself to what he shows on his site. That means I'm forced to essentially build my own with the help of a good muffler shop. Ed will provide me with all the advice I'd ever need plus all the hardware I'd need to get the header built, just not the actual build.


On an interesting side note, Ed's suggestions follow quite closely with the www.headerdesign.com results I showed in the graph. My design goal that I gave Ed was for a midrange setup, something along the lines of level 4 tune on HeaderDesign. Following that level 4 tune, we see the same outer 1.5" primary diameter as well as the 36" primary length. The collector is pretty much on the ball too. The only difference would be the exhaust design, but one should realize that cats and mufflers of different brands/models and sizes vary quite a bit. I figure Ed is suggesting to stay with the 2.25" piping all the way through to not run the risk of restricting the exhaust too much by going too small. However, I'm hoping that well chosen cats and muffer specifically built for high flow would prevent losses. If so, I may step down to a 2" setup.


I'll also state that I feel the $40 cost is worth the info received. However, most of the general info provided, good, quality info, is available online and discussed anyways. www.headerdesign.com is quite extensive in its discussion, and the article links I initially provides also repeat a lot of the core concepts. Even www.headersbyed.com offers a large amount of info right on their site.

I will also point out, his suggestions to me are specific to my desired build. If you wanted your car geared differently, had a different physical engine/setup, and wanted different end goals, you would be given a different set of suggestions. He does emphasize that he suggests setups on an individual specific basis. My goals are different from yours, so he taylors his advice to that.

An interesting side note is that although he offers only classic, domestic premade options, he's not new to the small car, import scene. He simiply feels there's no demand to justify any buidling of quality products. He and his family owns/have owned several Hondas, a Mitsubishi or two, and he actually plans on buying a Subaru Forester in the near future when his old Mitsu van dies on him. You may have noticed, his responses from the questionare is personaly and by him. The personal touch and care is an amazing aspect to provide by any company. We may actually see him on these forums in the not-so-distant future. Wouldn't that be interesting. Maybe we can get him and TiC and/or Maddad together and get us some killer headers made. No offence to Cobb and TWE of course. From what I've come across so far and from suggestions from Ed, it does seem that both Cobb and TWE do have their headers geared a tad bit too high, providing larger primary diameters and shorter primary lengths than suggested by Ed or HeaderDesign. The gains over stock are obvious, yet, there may be even more to gain.

Definately interesting stuff.
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