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    Results 1 to 14 of 14
    1. #1
      Join Date
      Sep 2010
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      Orange County, CA
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      Exhaust fabrication question

      How do you calculate the angles and lengths when trying to put an offset into an exhaust pipe? I would be cutting and welding the offset from pre bent mandrel tubing. For example, I want to move the exhaust pipe over 1” to the side. Thanks

    2. #2
      Join Date
      Sep 2007
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      York, Pa
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      I just eyeball it until it makes sense. I've done some high end exhaust and headers just eyeballing and making reference marks with a sharpie. Occasionally I will draw some reference angles on the workbench so I can duplicate left and right sides but I definitely don't spend much time on calculation.
      Justin Snow

    3. #3
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      Sep 2010
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      I’m not sure about the geometry but 1” isn’t a big offset. Over what length do need to make the offset? A couple of pie cuts may get you there. One cut to change the angle and an opposite cut “x” distance down the pipe to continue in the original direction. Don’t even cut all the way through. Leave just a tab to hold it togeather.
      I’d practice with a cardboard tube and tape.
      1966 Chevelle, 3.6L/217 CI, 4 cam direct injected V6, 6 speed auto, full Hotchkis suspension, 4 wheel Wilwood discs, white w/red interior, cowl hood. 3260 lbs w/full tank. Built for 35 mpg. So far 32.

    4. #4
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      Sep 2010
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      Thanks for the info. I’m trying to make a bend similar to this picture that I found online. I thought there might be a formula that would tell you how many degrees each direction, and maybe what lengths to make the bend to adjust the offset amounts. But I suppose I could just eye it and get pretty close, that’s how I end up doing most thing anyhow.
      Attached Images Attached Images  

    5. #5
      Join Date
      Feb 2013
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      It's just trigonometry if you're dealing with standard offset angles. Basically figuring out the vertical leg length of a triangle.

      I whipped up a CAD model and table for some common distances when I was working on mine.
      Attached Images Attached Images

    6. #6
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      Quote Originally Posted by JustJohn View Post
      It's just trigonometry if you're dealing with standard offset angles. Basically figuring out the vertical leg length of a triangle.

      I whipped up a CAD model and table for some common distances when I was working on mine.
      Nice drawing. I would guess that changing the 45s to 30s would get close to a 1 offset. I always wished I knew how to use CAD but never had a need.

      1966 Chevelle, 3.6L/217 CI, 4 cam direct injected V6, 6 speed auto, full Hotchkis suspension, 4 wheel Wilwood discs, white w/red interior, cowl hood. 3260 lbs w/full tank. Built for 35 mpg. So far 32.


    7. #7
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      Thats awesome, thanks. I see in your drawing, for a 2.2 offset, youd need no additional section length. How would you accomplish a smaller that 2.2 offset? I assume you change the angle from 45* to something smaller, depending on how much offset? And if you wanted to make a larger offset, while keeping the section length short, youd just use a larger angle?

    8. #8
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      Nov 2006
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      Quote Originally Posted by JustJohn View Post
      It's just trigonometry if you're dealing with standard offset angles. Basically figuring out the vertical leg length of a triangle.

      I whipped up a CAD model and table for some common distances when I was working on mine.
      Nice!
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain

    9. #9
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      Quote Originally Posted by 67-LS1 View Post
      Nice drawing. I would guess that changing the 45’s to 30’s would get close to a 1” offset. I always wished I knew how to use CAD but never had a need.
      Look up Google sketchup, it's free 3D modeling software with a large user base. Can usually find answers to your questions or find a forum with responsive people to help you out. I started out on it years ago designing speaker enclosures.
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
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    10. #10
      Join Date
      Feb 2014
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      12
      Country Flag: Canada
      If you have a friend whos an electrician ask him to use his math skills. Its basic trig and a right triangle, remember sin cosine and tangent.Your lengths and angles should be exact using math and a good chop saw.Or you could always just use a piece of cardboard scissors and a felt pen and wing it.I ended up using both methods.

    11. #11
      Join Date
      Feb 2013
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      684
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      You can't do it with the same 45 deg mandrel bends off the shelf. Ace Race sells a tight radius bend which saves ~ 1/2". Otherwise, you're looking at cutting into the bend or using less than a 45.

      If I get ambitious today I'll put together some line drawings with different off the shelf bends.

      Quote Originally Posted by 65 drop top View Post
      Thats awesome, thanks. I see in your drawing, for a 2.2 offset, youd need no additional section length. How would you accomplish a smaller that 2.2 offset? I assume you change the angle from 45* to something smaller, depending on how much offset? And if you wanted to make a larger offset, while keeping the section length short, youd just use a larger angle?

    12. #12
      Join Date
      Feb 2013
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      684
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      Quote Originally Posted by 67-LS1 View Post
      Nice drawing. I would guess that changing the 45s to 30s would get close to a 1 offset. I always wished I knew how to use CAD but never had a need.
      It's the bend radius that drives some of it. You can't have a negative "B" length.
      Somebody mentioned 15 degrees? Not my choice to work with but:
      2.5" Mandrel Bend Radius, 15 Deg Bend Angle
      Offset A Section length B
      0.5 0.944
      1 2.875
      1.5 4.8
      2 6.74
      2.5 8.67

    13. #13
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      Feb 2013
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      684
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      2.5" Mandrel Bend Radius, 30 Deg Bend Angle
      Offset A Section length B
      1.0" 0
      1.5" 1.1
      2.0" 2
      2.5" 3
      3.0" 4

    14. #14
      Join Date
      Sep 2010
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      Orange County, CA
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      Awesome! Thank you. How does pipe diameter effect this, going from 2.5 to 3?