Vacuum lines diameter
 

Hello!

I want to replace quite a few of my vacuum lines. My question is how important is the diameter? I see 3mm (FPR), 4mm and 6mm (BOV, wastegate etc.) lines are used now. Can i use 4mm everywhere? (it is easier and more tight to T plug them if the diameters are same). I know a vacuum splitter box would solve this problem, but i don't want to buy one yet.

I have noticed on my lame NB A/F gauge, if i swap to 4mm vacuum line (iso OEM 3mm) on FPR the fuel is not that rich in closed loop mode (not big difference, but slighty less fuel added somehow).
Does that give much weaker vacuum signal if i split them 3 ways? (MBC, BOV and where it goes originally from IM).

The car is B16A2 Civic.

Re: Vacuum lines diameter
 

I use 4mm just about everywhere on my vac lines, the only one line that I do give a solid signal (not tapped) is my wastegate signal. Boost gauge/BOV etc can be tapped off FPR/PCV etc etc.

Re: Vacuum lines diameter
 

I read tapping FPR is not suggested. I tapped to a vacuum line behind IM (going to some kind of magnetic? valve). Seems to be fast and strong vacuum signal.

Then i go for 4mm everywhere.

Thanks...

Re: Vacuum lines diameter
 

I don't know where you read that but as long as I can remember everyone and their mom has been using the FPR line, and this isn't just poor diy honda guys.