How to route a hose that carries nothing?

[Arde]

There is a debate brewing between two gurus, the perfectionist DQ and the detail obsessed SFDon.
DQ argues that a small vacuum hose/tube between the front carb and the distributor should be routed along a shortest path, while Don and my car use a very long path inside the conduit that carries the ignition wires.

I say vacuum is the absence of matter, so that hose is not carrying anything, so who cares about the route of a hose that carries nothing...

If DQ is right I will have Don himself fix it for me when he visits the house in the coming week... If Don is right I will have Don open a red wine and enjoy his victory while doing nothing about a hose that carries nothing.

Feel free to vote, operators standing by.

 

[sfdon]

Can I vote for myself???

 

[Thomas76]

My engineering brain knows that a longer hose will have slower reaction time, and will suffer from vac drop over distance. (There is a formula for it, so it's gotta be true).

Now, in the real world does that change the vacuum advance enough to notice a difference??

 

[stphers]

Actually if I remember right, the hose's ran thru the ign wire tube but they weren't the silicone vacuum line all the way thru, they just used that at each end and it was a smaller PVC tubing that was in the tube.

Thanks, Rick

 

[coupedegrace]

Can I vote for myself???

Yes, although some of our more refined members might consider it gauche.

 

[Stevehose]

Actually if I remember right, the hose's ran thru the ign wire tube but they weren't the silicone vacuum line all the way thru, they just used that at each end and it was a smaller PVC tubing that was in the tube.

Thanks, Rick

Yes I had this on mine when I bought it.

 

[Mike Goble]

First off, it's not a vacuum. It's an area of low-pressure air that flows one way or the other, depending on the ∆P between the vacuum can and the intake manifold. There is a curve associated with the VA can, it starts advancing at some measure of vacuum, say 5 inhg, and is all in by about 10-12 inhg. The volume of the VA can behind the diaphragm is pretty small. We're not talking about moving a lot of air or a huge change in pressure.
My wager is that you will be unable to tell the difference between the short and long lines.

 

[jmackro]

My wager is that you will be unable to tell the difference between the short and long lines.

Yes, because the signal moves at the speed of sound at whatever pressure is in the line (which, as Mike points out, ain't zero). And at the speed of sound, the distributor is going to get the message pretty quick, regardless of whether the tube is as short as possible, or somewhat longer. So the length and routing of the tube is more a matter of pleasing the concours judges than of influencing your lap times.

 

[deQuincey]

There is a debate brewing between two gurus, the perfectionist DQ and the detail obsessed SFDon.
DQ argues that a small vacuum hose/tube between the front carb and the distributor should be routed along a shortest path, while Don and my car use a very long path inside the conduit that carries the ignition wires.

I say vacuum is the absence of matter, so that hose is not carrying anything, so who cares about the route of a hose that carries nothing...

If DQ is right I will have Don himself fix it for me when he visits the house in the coming week... If Don is right I will have Don open a red wine and enjoy his victory while doing nothing about a hose that carries nothing.

Feel free to vote, operators standing by.

Mine is not a result of my design, hence it can not be attributed to me, this is only how I received my car, and I have seen it routed this way in at least 4 more cars, here pictured the short path

interested to learn more about this

 

[sfdon]

It’s the tubes…

 

[stphers]

And where I see 2 grommets around the ign leads, original was just a rubber ring like an o-ring

Thanks, Rick

 

[deQuincey]

Yes, because the signal moves at the speed of sound at whatever pressure is in the line (which, as Mike points out, ain't zero). And at the speed of sound, the distributor is going to get the message pretty quick, regardless of whether the tube is as short as possible, or somewhat longer. So the length and routing of the tube is more a matter of pleasing the concours judges than of influencing your lap times.

more a matter of pleasing the concours judges

if you indulge me in considering also a matter of maintenance; when you remove the sparkplug cable tube i prefer not to have a vacuum hose laying around

 

[Ohmess]

Carburetors. That is the answer to the question. DeQ has carburetors in his car. Don hates carburetors. If you ask Don about details on a carb car, he will reply "does not compute."

 

[sfdon]

Factory pipes and Ricks factory o-rings

 

[sfdon]

The shop has changed…
Ed Kaufman joined the team last year. Ed is a BMW mechanic with an incredible 50 years of experience. Ed started with Weber BMW when he was a young lad.
Ed knows carbs….

 

[deQuincey]

View attachment 184752View attachment 184753



Factory pipes and Ricks factory o-rings

ther is very interesting info here @sfdon



part 11, wow, never saw it, but,

- the description says 2 units, if one is for that vacuum where does the other go ?
- in the drawing there is no seven tubes, pipes or cables, coming out from the black big tube in the other side, ...hummm

 

[sfdon]

Two for vacuum.

The pipes are different colors so no confusion.

One for vacuum advance
One for vacuum retard

black hose
white hose

 

[Honolulu]

Thomas76, post #3 above, and Mike Goble in #7, there will only be loss if there is flow. In lines where there is negligible flow, there is negligible loss, e.g., vacuum line from carb to distributor.

For me, vacuum or pressure hose, the shorter the better, less to go wrong, get in the way or tangled with other things, confused with something else.

 

[Arde]

Fascinating! I had to go check what I have.
Yes, there are two! They go to opposite side of opposite carbs. Why?
And what does Don mean by retard? I thought that more vacuum always means more RPMs therefore more advance.

Apologies my engine bay is not as shiny as DQ's.

 

[sfdon]

Key is to make sure they aren't reversed!