The tubes I purchased from Speedway Motors, it is their 1 ¾ combo mandrel bend pn# 91013872. I purchased 15 pipes.
The only thickness they come in is 16ga. At about $14 ea they are a good deal for the amount of tube you get and that it includes both a U bend and a 90 degree bend.
Most companies want $15 for just a U bend. I also like how these tubes do not come full of grease like some companies tubes do. This saves having to clean all the pieces with solvent.
They are bare steel that is covered in a light oil that wipes off with Brake cleaner. I also prefer bare tubes to aluminized ones. This saves having to sand the coating off of all the ends to get a good weld at the joint.
16ga tubing has a .062 wall where as the more common 18ga has a .049 wall. This makes the 16ga tubing heavier. I am not concerned about the added weight on my car.
As part of my design, I use the most direct route for the cyl’s that are the farthest away from the collectors. As the cyls move closer to the collector I run the pipes in increasing longer routes to offset the diminishing distance. This will help keep the pipes to a more similar length.
I made a simple tool out of a piece of 2X4, a deck screw and 1/16 TIG rod. This enabled me to mark the tubes for cutting at different degree angles referencing from the center of the radius.
It is difficult to run tubes if you don’t know where to run them to. I made this Erector set looking fixture to mount the collectors so I would have a target to run to. Because I am going to exit at a angle to clear the A/C condenser I positioned the collectors close to the engine. This makes the bends tighter around the block. If I were to exit out the rear of the car I would have moved the collectors much closer to the rear of the car to get a more sweeping motion with the primaries
Here are the collectors mounted in the fixture.
