Exhaust fabrication question

[65 drop top]

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

[GNon18s]

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.

[67-LS1]

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.

[65 drop top]

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.

[JustJohn]

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.

[67-LS1]

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.

[65 drop top]

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?

[dhutton]

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!

[Hotwire]

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.

[proper]

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.

[JustJohn]

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.


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?

[JustJohn]

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

[JustJohn]

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

[65 drop top]

Awesome! Thank you. How does pipe diameter effect this, going from 2.5” to 3”?