I'm getting ready to install my boost gauge and would like to use some braided stainless line for about 6 or 8 ft. My question is what size line should I use? Thanks in advance
The smallest you can find. It doesn't hurt to go bigger, but it doesn't help either.
It's cheaper and easier to route when it's smaller.
How far are you planning on running the braided stainless lines? If you are running it anywhere near any wiring you need to be very careful to prevent the braided line from rubbing through the insulation, especially in tight places such as a grommet through the firewall.