As the title says I want to replace all my vacuum hose with silicone hose. What is the best size (mm) to get? I was originally thinking 4mm but I'm not sure if that's too small. Somewhere between 4-6 mm is what I'm thinking but I'm not 100% and rather know what stock size of the boost lines is. Thank you in advance for any help.

 

I think hose techniques does a hose kit with a variety of sizes and colors. They are also thick to avoid collapsing.

 

Just did a changeover with the Vibrant silicone hose pit kit on my 8 year old evo 7. Monitoring it for long term use...

the vac lines use a 5/32" (3.75mm) hose of which you get about 10 feet. I replaced the P E A lines as well as the one at the diaphram port with this size.

the kit also has a 3/16" (4.5mm) one that you can use for the BOV/ recirc. valve line.

initial feedback: My boost used to be settling between 19 and 20 psi... now with the change I noticed a steady 21 psi...

Vibrant claims their hoses wont collapse, so will keep an eye for the long term use.

 

I bought mine here http://www.boostcontroller.com/index.php?category=8
3.5mm and 4mm