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Engine Header design and tuning

Discussion in 'Powertrain' started by Milky, Feb 8, 2014.

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    Milky Enlarged Member

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    In typical Milky fashion, i am up late at night pondering things to do to my car. crunching numbers and such. tonights episode involved, you guessed it, the exhaust header.

    One of the biggest issues with our chassis is the lack of a proper aftermarket header. Now, i have a friend who is a damn good fabricator and i have talked with him about making a proper header for this car. down side is it wont be cheap. but it will be right and properly tuned for the car. I plan on having one custom header made for my car first. since i plan on revving the little old 1zz to close to 8000 rpm, i am going to design and build one around such. ill give the math and everything for each header i crunch numbers for.

    so heres what started it all for me tonight:
    http://www.carcraft.com/techarticles/header_basics/size_objectives_conclusion.html

    Matching Headers to Objectives

    If we know any two of the three previously mentioned variables (piston displacement, rpm, or primary-pipe diameter), we can apply some simple math to solve for the other. Here's how that works.

    1. Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Given this relationship, we can perform some transposition to solve for the primary-pipe cross-section area.

    2. Primary pipe area = peak-torque rpm / 88,200 x displacement of one cylinder. We can also determine the required displacement of one cylinder (multiplied by the number of cylinders for total engine size) by:

    Header Tech Tighten Flange Bolts Out of all the variables to consider, one of the most important is that the headers fit th
    3. Displacement of one cylinder = Primary pipe area x 88,200 / peak-torque rpm.

    Equations 1 and 2 provide a method for determining peak-torque rpm (as contributed by the primary pipes) if you have already selected a set of headers and know the engine size. In equation 3, primary-pipe area can be determined if the desired peak-torque rpm and engine size are already known. It will also calculate engine size based on a known set of headers and rpm at which peak torque is desired.

    Here's an example of how this approach can work. Suppose you have a 350ci small-block (43.75 cubic inches per cylinder). A primary-pipe torque boost around 4,000 rpm is your target engine speed. The choices for pipe size are 15⁄8 inches, 13⁄4 inches, and 17⁄8 inches. If we assume a tubing wall thickness of 0.040 inch, each of these od dimensions requires subtracting 0.080 inch when computing cross-section areas.

    Using the formula, Area = (3.1416) x (id radius) x (id radius), we obtain the following cross sections: 15⁄8 inches = 2.07 square inches; 13⁄4 inches = 2.19 square inches; 17⁄8 inches = 2.53 square inches.

    Header Tech Cyl Head Camshaft Piston Remember that headers are just one part of the power equation. When trying to improve powe
    Plugging each of these values into equation 1, we find the selection of peak torque becomes (in the same order of pipe sizes), 4,173, 4,415 and 5,100 rpm. Based on an intention to provide a torque boost around 4,000 rpm, 15⁄8-inch-diameter primaries appears to work. In accord with our previous comments about primary-pipe length, extending these primaries will increase torque below 4,000 rpm at the expense of torque above this point, which is an additional tool to manipulate a torque curve about its peak (see "Torque Peaks").

    While this method will not predict header-pipe area as precisely as some contemporary computer-modeling programs, it can be a valuable quick-and-dirty tool when making decisions about header choice or application of sets already on hand.



    Read more: http://www.carcraft.com/techarticles/header_basics/size_objectives_conclusion.html#ixzz2sj0d55Y7

    the following was taken from this site:
    http://www.600scene.com/index.php/a...-101--header-basics-a-guide-to-understanding-

    You have probably heard words like: back pressure, scavenging, tuned length, merged collector, rotational firing order, compatible combination and many others that meant something, but how they relate to a header may be a little vague. This article should give you a basic understanding of how a header works, what the terminology means, and how it plays a part in the header's performance gains.

    The first misconception that needs to be cleared up is that a header relieves backpressure, but a certain amount of backpressure is needed for optimum performance. Just the opposite is true. A good header not only relieves the backpressure, but goes one step further and creates a vacuum in the system. When the next cylinder's exhaust valve opens, the vacuum in the system pulls the exhaust out of the cylinder. This is what the term "Scavenging" means.

    The first consideration is the proper tube diameter. Many people think "Bigger is Better", but this is not the case. The smallest diameter that will flow enough air to handle the engine's c.c. at your desired Red Line R.P.M. should be used. This small diameter will generate the velocity (air speed) needed to "Scavenge" at low R.P.M.s. If too small a diameter is used the engine will pull hard at low R.P.M.s but at some point in the higher R.P.M.s the tube will not be able to flow as much air as the engine is pumping out, and the engine will "sign off" early, not reaching its potential peak R.P.M. This situation would require going one size larger in tube diameter.

    The second consideration is the proper tube length. The length directly controls the power band in the R.P.M. range. Longer tube lengths pull the torque down to a lower R.P.M. range. Shorter tubes move the power band up into a higher R.P.M. range. Engines that Red Line at 10,000 R.P.M. would need short tube lengths about 26" long. Engines that are torquers and Red Line at 5,500 R.P.M.s would need a tube length of 36". This is what is meant by the term "Tuned Length". The tube length is tuned to make the engine operate at a desired R.P.M. range.

    The third consideration is the collector outlet diameter and extension length. This is where major differences occur between four cylinder engines and V-8 engines. The optimum situation is the four cylinder because of it's firing cycle. Every 180 degree of crankshaft rotation there is one exhaust pulse entering the collector. This is ideal timing because, as one pulse exits the collector, the next exhaust valve is opening and the vacuum created in the system pulls the exhaust from the cylinder. In this ideal 180 degree cycling the collector outlet diameter only needs to be 20% larger than the primary tube diameter. (Example: 1 3/4" primary tubes need a 2" collector outlet diameter.) The rule of thumb here is two tube sizes. This keeps the velocity fast to increase scavenging, especially at lower R.P.M.s. Going to a larger outlet diameter will hurt the midrange and low R.P.M. torque.

    The amount of straight in the collector extension can move the engines torque up or down in the R.P.M. range. Longer extension length will pull the torque down into the midrange.

    Engines that "Red Line" at 10,000 R.P.M. would only need 2" of straight between the collector and the megaphone. This is just enough length to straighten out the air flow before it enters the megaphone. This creates an orifice action that enhances exhaust velocity.
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    Milky Enlarged Member

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    on to my header design, i plan to use the oem outlet for the down pipe as the exit, much like my m2/megan header does now.

    using the first sites formulas for finding pipe diameter
    2. Primary pipe area = peak-torque rpm / 88,200 x displacement of one cylinder.
    i came up with this
    1.77721 =5700/88200*27.5 (110ci/4)

    so roughly a 1.75 in pipe will be needed for a torque peak around 5700. this is MY desired torque peak since i plan to be revving higher. as stock or close to stock engine would be as seen below.

    1.371=4400/88200*27.5

    now that will give a torque peak around 4400 rpm like stock. and frankly, looks close to the stock manifolds diameter just from eyeballing it. LOL

    now onto header length. the target rpm i was shooting for was 7750, a little shy of 8000 but thats ok. remember that i am also supercharged and i have the blower to fill in the low end, this is all to bring the top end power to life. according to the second site a 10k rpm engine needed about 26in primary lenghts where as a 5500 rpm engine needs about 36in length.

    the difference being 4500 rpm and 10 inches (hehehe). so i shot for the middle of the road. 7750 is dead in the middle and is a 31in primary length.
    the first site also states that if a 1.75 in primary is used, then the collector outlet should be no more than 2 sizes up. well lucky for us, the oem pipe diameter is 2in. EXACTLY 2 sizes up. so i will need a fuck ton of 1.75 in 304ss pipe, a 304ss 1zz header flange and a 304ss 1.75in in 2in out merged 4-1 collector. this project will take some time, but i figured i would start a thread now and throw the info out there.
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    MacktasticSlick TRD whore with 36,000 posts, bitch

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    Car craft is always good for that shit, that's why I subscribe. They also had an article a while back showing this one product from a company that let's you custom build your headers using little pieces first, which are all adjustable with angles and straight pieces, to allow the tweaking of designs, angles, clearance issues, all of that, before ever touching a piece of metal. I'll see if I can find it, I don't remember the company name, but I know these things were yellow lol. I have 4 years of magazines to go through in my storage.
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    Milky Enlarged Member

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    hell yeah. i was going to make a jig using a spare 1zz and oem exhaust manifold in my basement, measure and mock up a firewall and ps to make sure i got the clearances right
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    cBass buffalo bell lover

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    can we get a 2zz header aswell?
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    MacktasticSlick TRD whore with 36,000 posts, bitch

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    Milky Enlarged Member

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    Maybe
    [IMG]
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    MacktasticSlick TRD whore with 36,000 posts, bitch

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    cBass buffalo bell lover

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    MacktasticSlick TRD whore with 36,000 posts, bitch

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    James Bullshit Police

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    I am now pretty interested in this. I think a good place to start would be PPE, because of their history.

    I like the math, but I hope that PPE has incorporated some tuning/testing into their tubing areas and lengths.

    For the NA 1ZZ, they start with a 1.5" then step up to 1.625", then parallel merge collector to 2.25" outlet.

    The S/C version has 1.625" all the way, but stays the same otherwise.

    These looks like this so I don't think they would clear the firewall:
    [IMG]

    However, they have one for the MR2-S that looks like it might fit! It's 1.5" all the way through so more suitable for NA, but if it bolts on, who cares!! A small bend may be needed to connect to the cat in this orientation though.
    [IMG]

    But the real reason for this post is that they also sell a good collector just for you:
    [IMG]
    [IMG]

    http://www.ppeengineering-onlinestore.com/category.sc?categoryId=24
    http://www.ppeengineering-onlinestore.com/Parallel-Merge-Collector-1-7-8-4-1-PM4187.htm
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    James Bullshit Police

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    It looks like OBX makes a copy of the PPE header for MR2 Spyders:
    [IMG]
    [IMG]
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    cBass buffalo bell lover

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    Who will be the guinea pig?
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    Goldy Well-Known Member

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    Irvin Well-Known Member

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    I thought about this already. And I actually already looked at several of those headers. PPE, OBX, MRS 2zz swap headers. They all stick out too far back. I asked MWR to measure from the flange to the most rear portion of the runners before turning down. They are about 3-4 inches too far. You will need to chop the flange off and reweld it closer to the turn down portion.
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    cBass buffalo bell lover

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    But that one guy with the AE111 2ZZ swap actually had no trouble fitting it on his chassis....thought i showed you guys those pictures...
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    Irvin Well-Known Member

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    You never showed us the pictures of the header. We know the motor fits. that's the easy part
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    James Bullshit Police

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    Which header?

    MR2 2zz swap header?
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    Irvin Well-Known Member

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    He doesn't know


    You only have 6-8 inches from the back of the head to hitting something in the back. None of the 2zz swap headers have header turn downs that short. You'd have to modify any of those headers
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    cBass buffalo bell lover

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    Irvin Well-Known Member

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    It would be easier if you just post the pictures
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    James Bullshit Police

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    It is the MWR MRS 2ZZ swap header.

    [IMG]

    [IMG]

    [IMG]

    Not quite the same since it's a coupe, but it looks like there might even be less room in this engine bay, but I'm not sure.

    [IMG]
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    crolla "Wait did I just lose to a corolla?"

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    James Bullshit Police

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    MacktasticSlick TRD whore with 36,000 posts, bitch

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    Shits gonna get real

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