Sizing for vacuum hoses.

[masterofsinanju]

I've recently found some cracks and hole in two of my vacuum hoses. I had some vacuum hose lurking in the shed and I've replaced the old hoses that had perished. The idle hunting issue I had intermittently seems to have been resolved although I think my idle is now a little higher than it was before (about 200rpm more).

I'm now happy with the idle characteristics but I am curious to know if the hose diameter has a significant effect on how the engine runs. The hose I used was a slightly smaller inner diameter, although it didn't take much effort to fit it on the barbs. The hoses in question go to what I think is the vacuum control valve.

Obviously a smaller diameter tube has a restricting effect, especially at higher flow rates.

What I don't know is how much air these are meant to flow. If the volume they pass in a given unit of time is low then perhaps the smaller diameter doesn't matter. Or maybe I'm setting this up to bork the engine.

I'll grab the correct diameter hose next time I'm heading past a shop, but I'd still like to know if it makes a difference.

[oldcorollas]

if it is a signal hose, I don't think it makes a difference.
the MS guys used long lengths of vac hose for the MAP signal during development, and saw no difference.

for idle up/bypass... mayyyybe? probably not?

give them a little squeeze to reduce the diameter a bit and see if it makes a difference?

[masterofsinanju]

Thanks OC.

For the record, doesn't seem to make a lick of difference.

What does make a difference is BHG. So the whole head is going to get serviced. Will replace more hoses then as well.