headers length

Discussion in 'Gas Engines' started by sinus, Jun 26, 2014.

  1. sinus
    Joined: Feb 2008
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    sinus Junior Member

    Hello;


    Any idea what is diferent betwen length of car headers and marine headers for same engine, same rpm and both 4-1?
    I have no idea how shorter must be header 4-1 for marine becouse of water cooling jacket.
     
  2. jehardiman
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    jehardiman Senior Member

    If anything, they should be a little longer (better scavange to keep the valves cooler due to generally higher loading for a marine engine). Most marine header systems don't have water jackets for arrangement reasons (i.e. most are external exhausting over the transom to atmosphere). If they have any cooling it is normally water injection in the header (mist) or collecter (flow) to cool the flexhose to the transom baffles. There are jacketed dual tube systems out there for fully enclosed operations, but they are pricey and usually for very specific engine/hull combos or custom.
     
  3. Westfield 11
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    Westfield 11 Senior Member

    "Zoomie" headers do indeed exhaust over the transom and are air cooled and made from single wall tubing. These are the closest to an automotive header, but nowdays are mostly found on V-drives and flatties. All the other ski and sport boats with V8's use water cooled headers with water jackets at the exhaust ports on the heads and use water mist to cool the gasses to keep the flex hose from burning up. These use double walled tubing with water between the two. Google Gil marine exhaust to see some.

    I can rest my arm on my headers comfortably even after running for an hour or so at speed. This is on a 530hp big block Chevy.
     
  4. sinus
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    sinus Junior Member


    No trouble, we will made it. This winter we will build alu casted headers with Precision cast-(printed wax modell) and conected on closed cooling sistem, it mean no more see water in headers!
    We have double Hyabusa with 15% more power each than originall (cca 410 bhp at only 500 pounds weight together with ZF.) and they work really well, owerheating it is no trouble at all. Calculater lenght of headers pipes it is 0,7 m (2,31ft) for 7.000 rpm and above, but for marine aplication they must be shorter, becouse of cooled exhaust gasses, this I know, but I do not know how much. I have no idea how much cooler are gasses when come out of marine headers and this is my trouble.

    http://s1.mojalbum.com/7712951_7712992_20837954/letalo/20837954.jpg?1403798358745
    http://s1.mojalbum.com/7712951_7712992_20837956/letalo/20837956.jpg
     
  5. slow fred
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    slow fred Junior Member

    The only way to really check the length needed for max HP would be on a dyno.
     
  6. sinus
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    sinus Junior Member

    We know exact length of dry headers, but marine headers? We can not build 5 diferent length. You mean to go on dyno with marine exhaust, or?
     
  7. Westfield 11
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    Westfield 11 Senior Member

    Why on earth would you want to use a Hyabusa engine in a boat? High Hp at High RPM and low torque does not make for a very good boat motor. High torque at lower RPM is what you want to turn a propellor.

    It is an interesting exercise in design and fabrication, but who would want to spend any amount of time in a boat with twin motorcycle engines screaming away at 10,000 RPM? It sure sounds like an unpleasant place to be although if you are a racer and in a competition, I suppose it would be worth it. Just wear your earplugs!!

    BTW, what sort of drive are you going to use? Adding its weight will bring you close to if not over 700 lbs, a 350 Hp Yamaha outboard only weighs 730 lbs and it comes with a warranty........ Seems like a lot of trouble to get 60 more HP.
     
  8. sinus
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    sinus Junior Member

    Please, this is not questions, but we find reasons to not use for example 502 HO engine, which is mastodont by dimensions, weight, fuel consumption and technology. 350 hp Yamaha it is to weak and efficiency of our drive is far better.


    Before we made decision we make lot of calculations and there are main reasons why we choice twin busas:
    - 410 bhp
    - 3.300 rpm on prop shaft
    - 800 Nm or more on prop shaft from 1.800 to 3.300 rpm on prop shaft, at 1.300 rpm on prop it is more than 600 Nm torque.
    - at 30 mph only 5,8 gallon and at 45 mph only 7,9 gallons fuell consumption etc.
    - it made far less noice than any big block with thru hull exhausts!
    - it need really small space and CG of boat it is wery low.



    We use MSA drive and Maximus ST 26" prop. Like i told it work, but over winter would like to cast alu headers with closed cooling and before of this would like control lenght.
     
  9. Petros
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    Petros Senior Member

  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's fairly easy to get primary tube length dialed in with a temperature sensor. A few hard "pulls" with the engine under load and the tubes will have a distinct hot spot. The collector is welded so the down stream flange is at this average point on the primary tubes. This will get you within a few percent of optimal. A dyno can dial it in further, though of dubious need, except in class restricted engines, where every last ounce of energy is talked out of the available HP.

    Stroke and bore ratios are very different on purpose built marine engines, so volumetric efficiency, cam lobe dimensions and duration (overlap +), etc. are also very different. The chart below shows how different this can be on just the bore and stroke, verses power density.

    [​IMG]

    The discussion can get pretty "deep" for the average guy, but generally, you'll want a "long leg" engine, rather then a typical automotive arrangement. Ultimately, you have to decide what type of propulsion you need and find an engine configuration better suited to this, rather than adapt an automotive configuration, which will work, but will be less efficient and the typical RPM ranges boats employ.
     
  11. 7228sedan
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    7228sedan Senior Member

    just out of curiosity, what kind of craft will you be powering with this engine? I have seen twin Busa motors morphed together for the RPE RP-V8 (http://en.wikipedia.org/wiki/Powertec_RPA). This are high revving high HP motors. As you are spinning a 26" prop, I assume that the boat is a light weight sport boat of some kind?
     
  12. sinus
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    sinus Junior Member

    - length 29 ft
    - wide 102"
    - simple 24 degrees V hull with wide 14", 16 degrees delta pad.
    - weight 3900 pounds fully equipped with out of drinking water and fuell.


    maded with infusion from:
    - honeycomb-hull
    - high density pvc foam
    - biax S-glass for deck
    - quax S-glass with 30% kevlar for hull
    - vinilester

    - drive MSA
    - prop labbed Maximus 15,25" x 26", short tube.


    Advantages of busas:
    - much, much specific lighter engines than any others, therefore lighter and more efficient boat.
    - small dimensions, therefore much more space inside in boat. We have engines under back seat and we do not need "swiming platform". It mean at least 1,5 m longer space for passangers.
    - extremly good torque "curve". Almost all working rpms have similary torque, it mean great efficiency from 40 mph-(less than 7,5 gall/hour) to the end speed.
    - nice holle shot.
    - exellent end speed resulted with light weight construction mostly becouse of light engines-always far over 70 mph.


    This fotos are 3 years old and there are existing exhaust with out of external skin. Comming winter we will print wax mould for precision casted alu headers and there fore I would like to know diference of lenght betwen:
    - dry exhaust
    - marine exhaust with water skin

    I do not want to make discusion why is our choice better than actually inboard dinosaurus, I not need education how bad is this choice, or how much better are other engines, what is correct stroke/bore ratio etc, I wish to know diferent of headers length if somebody know this. Exhaust gases have turbulent flow and it is simply to hard for my mathematic knowledge to make exact control of heat exchanges in headers.



    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]


    Please if somebody know diference of headers lenght for dry and marine exhausts.
     
  13. 7228sedan
    Joined: Nov 2009
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    7228sedan Senior Member

    I'm not looking to tell you that it is a good idea or a bad idea. I'm more interested in the originality of the design. Assuming the boat is set up correctly, and the engine puts out ample torque, you very well could be on to something. It seems like torque is usually forgotten about when most speak about engines. In a lighter performance hull it is not as critical as it is in a commercial or cruising boat. That being said, I'd have to guess that the length of the header wet or dry would be the same ideally. Also, the length would have to come into play with the diameter of the individual runners that you are using. Perhaps you could also post on offshoreonly.com. That forum specializes is offshore performance boats where long tube headers would be more commonly used as opposed to traditional marine exhaust manifolds. Granted, they are all likely to be mounted to traditional big block engines. There are many variables that need to be considered when designing headers, exhaust scavenging capabilities, diameter, shape, length. I know in an automotive application, I used 1 5/8 diameter long tube headers on a supercharged 306 ci v8. That engine didn't see the high side of 6000 rpm's but a few times. If I was going to be running that motor up to 8,000 or higher, I would have needed to increase diameter in order to obtain peak HP however my peak torque would have likely suffered. There is always a compromise. Best of luck and please keep us posted on the progress.
     
  14. sinus
    Joined: Feb 2008
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    sinus Junior Member

    I know. :)


    We have correct lenghts for dry exhausts, just I did not know what efect have cold water round of pipes.

    Round torque;
    I agree, that torque is important, but torque on pop, not on crank shaft. If you reduced 10.500 rpm on 5.200 rpm, will torque increase on 8,1 HO level, but not only at 3.500 or 3.700 rpm like at 8,1 HO, it is almost same torque all over working rpms of engine.
    Benefit of this choice it is 20% lighter boat (15% becouse of engines, 5% becouse of construction) and it mean that 390 bhp from busa made same specific power of boat like 450 bhp of big block.
    This 20% mean also better hole shot, smaller fuell tank becouse of less consumption...
     

  15. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Interesting setup, what is the ignition sequence? Normally, with the almost standard 1342 sequence for a four cylinder engine, I would expect the branches 1+4 and 3+4 to unite before the final y-junction, but not here, hence my question.

    Now to your original q; the length from valve to junction is related to the gas temperature, and is (as you well know) tuned for maximum scavenging effect at a certain rpm. A marine engine needs a "fat" power curve from midrange and up in order to suit the propeller power during acceleration and high loading. This is the reason you often find that the "breathing system" for a marine engine is tuned for a slightly lower resonance frequency than the automotive variant of the same engine.

    So, if you cool your exhaust (with the original pipe length), the pressure pulses will take longer to pass through the pipe. The effect is a reduction of the optimum rpm, just as if the pipe length had been increased slightly. This means that you may get exactly the right power characteristics with standard lengths and cooling; i.e maximum torque comes in at a slightly lower rpm. If you wish to keep the original characteristics, you have to shorten the length corresponding to the reduction in velocity of sound due to the colder gas. The exact amount of shortening necessary is depending on the heat transfer, but I have seen the difference to land in the 3 to 5 percent range with a cooled manifold.
     
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