Enter your username:
Do you want to login or register?
  • Forgot your password?

    Login / Register



    Results 1 to 14 of 14
    1. #1
      Join Date
      Sep 2010
      Location
      Orange County, CA
      Posts
      665

      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
      Location
      York, Pa
      Posts
      457
      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
      Join Date
      Sep 2010
      Location
      Martinez, CA
      Posts
      184
      Country Flag: United States
      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.
      Worlds Fastest LFX powered 1966 Chevelle, with a 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
      Join Date
      Sep 2010
      Location
      Orange County, CA
      Posts
      665
      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
      Posts
      799
      Country Flag: United States
      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
      Join Date
      Sep 2010
      Location
      Martinez, CA
      Posts
      184
      Country Flag: United States
      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 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.
      Worlds Fastest LFX powered 1966 Chevelle, with a 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
      Join Date
      Sep 2010
      Location
      Orange County, CA
      Posts
      665
      That’s awesome, thanks. I see in your drawing, for a 2.2” offset, you’d 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, you’d just use a larger angle?

    8. #8
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,487
      Country Flag: United States
      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
      1959 Apache Fleetside

    9. #9
      Join Date
      Jul 2008
      Posts
      453
      Country Flag: United States
      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
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁

    10. #10
      Join Date
      Feb 2014
      Posts
      14
      Country Flag: Canada
      If you have a friend who’s an electrician ask him to use his math skills. It’s 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
      Posts
      799
      Country Flag: United States
      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
      That’s awesome, thanks. I see in your drawing, for a 2.2” offset, you’d 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, you’d just use a larger angle?

    12. #12
      Join Date
      Feb 2013
      Posts
      799
      Country Flag: United States
      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.
      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
      Join Date
      Feb 2013
      Posts
      799
      Country Flag: United States
      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
      Location
      Orange County, CA
      Posts
      665
      Awesome! Thank you. How does pipe diameter effect this, going from 2.5” to 3”?







    Advertise on Pro-Touring.com