1. pishta

    pishta I know I'm right....

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    Question: If a normal N/A exhaust manifold on a good tune runs 200-600F could you theoretically cast one out of Aluminum? I know that sounds ludicrous but AL has a melting temp of 1000-1200 and can be cast with hobby grade equipment. Corvairs and Pontiac offered them to drag racers...Just a thought to cast Hyper-pak style 2X3 trees in AL for a mild build.
     
  2. Mopar-Mitch

    Mopar-Mitch Well-Known Member

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    I have a 2012 dodge challenger with the 3.6 pentastar V6, the heads are aluminum and the manifolds are cast in the heads, head and exhaust manifold all in 1. So I figure it should be possible.
     
  3. Go Mango

    Go Mango I drive it like I stole it

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    I'm probably wrong about this, but I think the tensile strength of aluminum would prohibit its use for headers on a street car. Too much flexing from the rest of the exhaust might cause an epic failure.
    Please correct me if I'm wrong.
     
  4. pishta

    pishta I know I'm right....

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    Water cooled Im sure.....I was aware of the exhaust cast heads (Ford straight six) but wondered how well they fared.
     
  5. pishta

    pishta I know I'm right....

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    I'm sure your correct. Even the cast iron Hyper packs have multiple pics of the rear ones welded at the flange. Maybe some sort of rigid exhaust on hangers and a flex connector like the modern transverse motor cars have.
     
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    • brian6pac

      brian6pac Well-Known Member

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      I built a street rod with a 400 chevy and had SS shorty headers and they turned colors and the owner said it was way to lean, I knew it was not so I called Keith Black and he told me that you want 1400 degrees 1in out of the port so I looked up a temp color chart for stainless and 1400 was a yellow blue if I remember right. A heavy load long pull I'm sure would be a lot hotter in the manifold.
       
    • pishta

      pishta I know I'm right....

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      1400F? Wow, that's hotter than I imagined but KB builds race motors, maybe a little hotter than a stocker? Here is a Toyota Land Cruiser lo-po motor that was recorded: "I screwed on a sensor (PT100 type) and use a digital indicator in a very visible site. The motor is a 2H without turbo, in a 1980 HJ60. After warm-up and then several km flat driving, there was a 2 km climb, at full throttle the maximum temp was 115 C (239 F). On flat again, going some 100 km/h it dropped to about 90 C (194 F). I did the same installation on our other LC (1987) with the 3B motor. On the 2 km climb, this one reached maximum of 305 C (=581 F), and cruising along afterwards it dropped to 205 C (401 F)..."
       
    • Pascamp

      Pascamp Well-Known Member

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      On circle track engines I've seen temps approaching 1600F. That's basically 2 dyno pulls every lap though. I don't have much experience with forced induction, but I've heard that they can run much hotter than that (2000+f).
       
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      • brian6pac

        brian6pac Well-Known Member

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        He told me any colder than that you would have problems with fouling plugs, I have a fluke temp meter that goes to 2500f and I put it on the outside of the header tube about 1in out and it reads around 650f - 700f and I'm sure it twice that inside the header
         
      • my68barracuda

        my68barracuda Well-Known Member

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        Exactly, the temperature at the inside wall of the exhaust manifold will be much higher than the outside wall. Remember some of the temperature is being dissipated to the air surrounding the exhaust manifold. And during an extended run at highway speeds you will see localized external manifold temps much higher than 600 F
         
      • DFX 340 Duster

        DFX 340 Duster FABO Gold Member FABO Gold Member

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        Well, Pishta, here’s a fun experiment. Remove the exhaust manifold and start the car. Grab a piece of aluminum weld wire and stick the end in the exhuast stream as it exits the port. If it doesn’t melt then draw up your plans for the aluminum manifold.
         
      • Go Mango

        Go Mango I drive it like I stole it

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        Great idea! But I wouldn't do it... you just think open headers are loud!
         
      • Go Mango

        Go Mango I drive it like I stole it

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        I don't think it's so much what temp they get to, as much as it is the normal operating temp and the stresses on the strength of aluminum.
        Even cold, the stress of the exhaust "flexing " would be enough to crack/break a header.

        I think.
         
      • pishta

        pishta I know I'm right....

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        I did start a 340 without manifolds once for about 3 seconds. Sounded like a Spitfire starting in a WW2 movie. Not real sure how the Corvair AL headers worked but they did....? Well, working with 16g isn't that hard, and is easily welded so....Ill leave AL to the cold side if the head.
         
      • DFX 340 Duster

        DFX 340 Duster FABO Gold Member FABO Gold Member

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        That's why I said it would be fun. The neighbors would be far enough that it shouldn't bother them too much. LOL I recommend aircraft rated ear plugs/headset of course.
         
      • DFX 340 Duster

        DFX 340 Duster FABO Gold Member FABO Gold Member

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        Good thought. I have over 30 years experience working for Douglas Aircraft and Boeing as a materials and process engineer. Aluminum has been used in primary aircraft structures for many decades and they experience many types of stresses. Different alloys have different physical and mechanical properties. It really is important to know to what temperature the aluminum would be exposed. The induced stress from having two different metals expanding at different rates (iron head vs aluminum manifold) would be mitigated to some degree by the exhaust gasket material and thickness. I believe that an aluminum exhaust manifold could be designed for the slant six application with enough knowledge of the operating temperature. Fabricating a few might be costly.

        Just my two cents.
         
      • RustyRatRod

        RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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        I've seen cast iron manifolds glow cherry red and orange from engines being out of tune. It takes over 1000 degrees F to do that.
         
      • DARTLARRY

        DARTLARRY Well-Known Member

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        How many cast iron manifolds have you seen with a crack, or weld repair? I don't think cast aluminum will have the tensile strength to hold up to the abuse an exhaust manifold has to take.
         
      • roccodart440

        roccodart440 Well-Known Member

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        I run a temp gauge on my diesels. They tell you to back out at 1200.. Now that is exhaust gas.. The metal you know gets hotter than that. I'd say cruise temps might be 600 to 800 but when towing or climbing grades they can go up pretty quick.
         
      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        I wonder what the temp gets to inside the aluminum combustion chamber, after 12 seconds.......
         
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        • pishta

          pishta I know I'm right....

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          Yeah, that is why I stressed a well tuned motor.
           
        • Garry in AZ

          Garry in AZ Building a 9 second Valiant FABO Gold Member

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          In the '60's Pontiac experimented with aluminum exhaust manifolds on their super stockers. They came with warnings not to run the engine for more than 20 minutes continuously or the manifolds would warp. There are aluminum exhaust manifolds for the marine market, but they have water cooling jackets. Anyone who has monitored a pyrometer on a turbo engine knows the temps can easily exceed 1000 degrees F.
          I know an engine run at Bonneville that had EGT probes about 2 inches from the cylinder head routinely saw 1400 degree temps when the tune was right.
           
        • roccodart440

          roccodart440 Well-Known Member

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          Same as a dyno pull or slightly less.
           
        • roccodart440

          roccodart440 Well-Known Member

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          It should be noted that momentary temps vs. sustained are 2 different things. In addition some of the racing engines that will tolerate higher than normal WOT and load temps often have other provisions to allow such as coated pistons, different clearances etc.
           
        • 69_340_GTS

          69_340_GTS Well-Known Member

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          If an aluminum alloy is OK to use as a head or piston material, I cannot see why it cannot be used for exhaust manifolds. It should not melt. But the strength issue is another problem. You might end up with manifolds 2X as thick as the iron, just for strength. Well, there goes all your weight savings!

          A356 alloy is commonly used for heads and blocks. Melts at about 1000°F.
           
          Last edited: Mar 15, 2019
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