Quick question ive been thinking about, is it better to run larger or smaller diameter vacuum lines? or does it matter?

not talking about the wall thickness, obviously thicker is better for that to avoid lines collapsing, but does the actual diamter of the line have any effect?

95 Avenger
ATX->MTX Swap
Holset HX40 @ 26 psi

I say run the largest the nipples will allow for a snug fit. I use 3mm on the wastegate/boostcontoller/turbo compressor. I use 6 mm on my BOV (attached to the old PCV on the upper intake manifold). This made my BOV very fast reacting. It used to surge when it shared one of the T-fittings connected to some other hoses. I think it is better to have a dedicated source for the BOV. I use 6mm on my boost gauge, because it fits the nipple very well on the gauge itself. I have replace every vacuum line with silicone and NEVER get leaks. I also used 8mm silicone hose for both my valve cover vents into the catch can. It fits the RRE catch can very well and it a tight fit on the valve cover nipples.

I also use wire ties(two on the boost lines) for every connection. If they break or become loose, I redo them asap. So far I never popped a line.

97 RS(PTE SC-61, Built Long Block, Electromotive Tec 3)It's Here!

Thanks for the reply i dont have any leaking lines or anything, and my bov is setup the same way as yours, a line off the pcv nipple. Mine also fluttered when i had it Tee-d off, so i gave it a dedicated line.

just wondering if smaller lines would be more responsive, like less volume to fill so its more effiecient? or would have a larger volume be more efficient. i realize its minimal, but every little bit, right?

guess im not so much interested in peoples setups, just looking for the theory behind vacuum sizing, if it at all matters

95 Avenger
ATX->MTX Swap
Holset HX40 @ 26 psi

I think the line from the compressor side of the turbo to the wastegate needs to be the shortest and smallest possible(within reason). Pressure causes the wastegate to open(not total air volume)and then regulates the boost. If the hose(volume) was larger, the pressure would fluctuate more and also take longer to fill the line. It may not make much difference, but the wastegate reaction might be a tad slower.

I think the BOV needs to be a dedicated source(like you said) and also needs to be the biggest line that that will fit on the nipple. Vacuum causes the valve to open and the more sucking action the BOV gets the faster it will blow off. The reason I say this is because the line I had before was the 3mm and the vacuum was less because it was off a T and that line was off another T. Between shifts the compressor would surge. Now between shifts, the bov blows off really fast and the amount of air released initially is much more. This tells me that the larger volume line along with the dedicated source is what is required.

I do not think any other vacuum sources make any difference in performance. As long as they are sealed, that is all that counts.

97 RS(PTE SC-61, Built Long Block, Electromotive Tec 3)It's Here!