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Thread: Fabrication technique for turbo exhaust flanges...

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    Senior Member turbokinetic's Avatar
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    Default Fabrication technique for turbo exhaust flanges...

    In the interest of encouraging others to take on projects like this - here is the procedure I use to make a flange to mount an exhaust pipe to a turbocharger, or make a mounting flange. It's pretty basic to some of you expert fabricators, but may interest those who haven't done much metalwork.

    This turbo is nonstandard. It is a Garrett VNT3 series turbo for a Hino truck. I can't order any flanges for it easily so have to fabricate them.

    If a gasket is available, it's pretty easy to use it for a pattern. In this case, the gasket will also have to be made eventually, so I can't use if for a pattern.

    This is the exhaust outlet of the VNT3 turbocharger. I need a flange to bolt up to this 3-bolt outlet for the beginning of a downpipe.





    The first step is to cut a piece of Avery self-adhesive label paper that will fit over the outlet. Just set it on the outlet and rub a (dirty) finger over the edges of the turbo flange and the bolt holes.





    Now that I have a pattern the shape of the exhaust outlet, I clean a place on my metal stock, and stick the self-adhesive paper down. First thing to do before the adhesive paper gets burned, scorched or ripped is to center-punch the 3 bolt holes.




    Once that is done, I locate a round object for a cutting guide to cutout the center hole in the flange. I'm going to be cutting it with a "plasma torch." This machine uses a jet of air heated by an electric arc so hot it will vaporize steel, stainless, titanium or anything else that gets in its way. It only uses electricity and compressed air.

    The plasma torch has a fairly large nozzle, that "offsets" the cut about 1/8" from the cutting guide. This old Briggs & Stratton starter drive happened to be just the size to make a cutting guide for this!





    TO make this cut, I first blow a hole through the center, and cut a slot to the edge before clamping the cutting guide to the metal. The plasma torch does not make a clean hole, especially cutting very thick metal like this (at the limit of this machine's capacity)





    Now, simply clamp the cutting guide (in this case the starter drive) and go around it.





    Once the hole is done, I use a fiberglass straight cutting guide to finish the triangle shaped flange. It's got to be offset the distance from the edge of the plasma torch nozzle to the jet hole.




    After that, I've got a blank cutout of the flange:





    Now the bolt holes have been drilled and it looks like it will line up nicely with the turbo outlet!




    Now when I'm doing the fabrication of the downpipe, I can weld the next piece of the pipe to this flange with ease. Looks like a 2.5" pipe will weld right in!




    So that is one way to create a mounting or exhaust flange for a turbo, without having any drawings, templates, or gaskets to go from. It looks home-made, and I used scrap metal to build it from. Cost me about 15 minutes of time and a little electricity!


    Once the downpipe is built, I'll grind the edges to eliminate the irregular shapes, and of course the pipe will be wrapped with insulation. This will be about the only part of the pipe that is visible.

    Later,
    David

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    In this specific case, wouldn't it have been better to use a 3bolt-flange header reducer of the correct size? Or is the thicker flange a must for a turbo outlet?
    -Andy

    '86 Eurosport VR coupe
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    Senior Member turbokinetic's Avatar
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    Quote Originally Posted by 86euro View Post
    In this specific case, wouldn't it have been better to use a 3bolt-flange header reducer of the correct size? Or is the thicker flange a must for a turbo outlet?
    In this case - it's an odd size. I wouldn't have a problem with a header reducer, but it would take longer to locate one than just to make the flange.

    Also - the header reducer flanges that I've seen here - are cheap, thin crap that would warp and bend way too easily!

    David

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    Senior Member bubblebob88's Avatar
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    Very nice write up, my buddy did kind of a small project like this. I like how it's quick and very effective, back in the metals shop class I helped teach in high school, a kid made a turbo exhaust flange for his s10 during our little welding tests.
    -John

    "Do you got a V8 in that Cutlass or something" -Some drunk hoosier barbecuing at a park

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    Senior Member turbokinetic's Avatar
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    Quote Originally Posted by bubblebob88 View Post
    Very nice write up, my buddy did kind of a small project like this. I like how it's quick and very effective, back in the metals shop class I helped teach in high school, a kid made a turbo exhaust flange for his s10 during our little welding tests.

    Thanks. It's not hard at all to do, just takes some experience and patience to get proficient with it.

    How'd the student's turbo S10 turn out?

    Thanks,
    David

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    Member OldsTurboDiesel's Avatar
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    Quote Originally Posted by turbokinetic View Post
    In this case - it's an odd size. I wouldn't have a problem with a header reducer, but it would take longer to locate one than just to make the flange.

    Also - the header reducer flanges that I've seen here - are cheap, thin crap that would warp and bend way too easily!

    David
    When fabricating, it is better to over-engineer than under-engineer. Exhaust components with a turbo system are very unforgiving. Nice job David

  7. #7
    Senior Member turbokinetic's Avatar
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    Quote Originally Posted by OldsTurboDiesel View Post
    When fabricating, it is better to over-engineer than under-engineer. Exhaust components with a turbo system are very unforgiving. Nice job David
    Thanks! Yep that is true. Especially on the turbine inlet side. Not only does it have all the heat and pressure of the pre-turbo exhaust, but it has to support the turbocharger, and can NOT have any loose welding splatter or slag inside the weldment.

    Later,
    David

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