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Pie cut exhaust

This is a discussion on Pie cut exhaust within the Technical forums, part of the Caferacer.net Forums category; Just thought I'd throw this up here. There's not a lot on the internets about this. Some. Not all in one place. But enough that ...

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Thread: Pie cut exhaust

  1. #1
    jcw
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    Pie cut exhaust

    Just thought I'd throw this up here.
    There's not a lot on the internets about this.
    Some.
    Not all in one place.
    But enough that I think I'll give it a try.

    Hopefully when I'm done, it'll be a nice synopsis of all I've learned.
    And, yeah, this is a project in process and not a retrospective presentation. So updates may be slow depending on my motivation.

    I trolled craigslist for a long time and picked up a used metal chop saw (carbide blade not the abrasive kind) for the project.
    Name:  39419_3_400x400.jpg
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    To be continued...
    hopefully

  2. #2
    jcw
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    Why am I doing this?
    The modified stock exhaust I'm using chokes down to less than 1" at various spots in the exhaust and I feel it is limiting high rpm power. Great torquey engine. But flat on top.
    Also, the stock exhaust limits ground clearance on right turns. I'm going to reroute for more clearance as well.

    If you buy pre bent mandrel tubing you are limited to a couple and sometimes only one radius bend. With pie cuts not only can you make any radius you want, you can vary that radius within a single bend as well.
    And because it's another skill that I want to learn.
    Last edited by jcw; 02-04-2017 at 08:27 PM.

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    Member 540nova's Avatar
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    Stainless or mild steel? Mig or tig?


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  5. #4
    jcw
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    Tig. I'm pretty decent at it. I don't own a mig.

    Steel for my first attempt. I'd rather not add the complexity of purging the tubing.
    Last edited by jcw; 02-04-2017 at 08:27 PM.

  6. #5
    Senior Member Andyshep's Avatar
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    Never heard it called pie cut, was always called lobster backed when I worked in fabrication, always wanted to make my own exhaust and will do one day, good luck and I look forward to the updates.

  7. #6
    jcw
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    Ok. So first the theory.

    I want small enough segments so that the result looks decent rather than some sort of kids Lego toy.

    10 segments per 90 degrees should be plenty. This means 9 degrees per segment.
    Since each pie cut or segment is cut on an angle at each end, then each side is 4.5 deg.

    I set the chop saw with a protractor to cut at 4.5 degrees. Hopefully.

    To set the centerline radius of the "bend" created by these segments I'm going to use an online program that calculates the width of the cut. I'll use solidworks to print up a cutting template.

    The biggest thing about cutting these segments is that the cuts must be made alternating +4.5 and -4.5. And the tube held in the exact same rotation for each cut.

    Right now I'm trying to figure the best way to make the cuts and ensure the tube is kept in the right rotational position.

    Pics to follow...

  8. #7
    jcw
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    Oh btw, can someone tell me what I like pie and CR.net have to do with one another?

    Please.....

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    Member 540nova's Avatar
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    No.


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  10. #9
    jcw
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    Here's a link to a post with the link to the excel program that calculates the width of cut for a given tube diameter and center line radius.
    Tube pie cut calculator

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    I never realized it was so complicated. I thought they just eyeballed it.


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