robot808

I am about to pull some vacuum from the spider on 82 for a BOV and a boost gauge. The ID of the line at the spider is larger than what I need it to be for those items. I have the fittings to reduce the lines to fit the items, but is there an effect of higher vacuum in the Skinner lines that will cause me any problems?

Also, can anyone tell me what my options for running wires inside the car from the engine bay on my 82? I have been through the fender by the hood release, any easy ways through the firewall? I am trying to get wires to the left side A pillar.
Thanks much,

Ducman82

i ran some wires down thru were the engine control wires and stuff are ( passenger side). are you using vac tube or hard line?

robot808

Silicon hose.

Ducman82

how small is the BOV and boost gauge nipples? the spider ports seem to be pretty standard size. as long as you have a clear vac line (no bends or kinks) you should be good to go with either of the sizes really

Jerry Feather

Air cannot suck, it can only blow. Vacuum is merely the absence of air and therefore, air pressure. When you remove the air pressure from one side of a diaphragm what does the "work" is the air pressure on the other side of it. By remoiving the air with a smaller line, it might take a little longer, but it does not increase the air pressure on the other side. You can only remove as much air pressure as that removed at the vacuum source. The smaller the tubing size and the longer the run will only reduce the ability to remove the pressure some amount, and in your case, not too much.

In short, vacuum is not a force in itself; it is merely a means of putting another force into effect.

Jerry Feather

Jerry Feather

As to the wires, since you are already in the left wheel well, why don't you run them along with the hood release cable?

Jerry Feather

robot808

That makes a lot of sense. I believe I am going from 6mm to 3mm with no bends or kinks in the hose.

robot808

Regarding the wire running, I was going that there might be a shorter distance than routing it through the fender. I think I might run short. Of course, I can lengthen them, just trying to save some work.

depami

Size doesn't matter; it’s how you use it that counts.

As Jerry points out, a smaller line will transfer less air in a given amount of time with a given vacuum source.

In which case if you were trying to evacuate an autoclave oven you would want a good sized draw line and pump.

Think of it this way: If you used a two inch diameter hose it would take quite awhile for your vacuum source to evacuate that hose to the point that the gauge would move. You could prove this by connecting your Mityvac to various hose sizes and count how many pumps it takes to create a given vacuum.

Likewise, any changes would be damped (not dampened) by all of that volume.

But you are simply running a gauge which has very little volume and no continuous flow so smaller is better. A larger line will simply cause more response delay.

In all actuality, the difference in the sizes you are talking about will not be noticed. Just make sure the hose is vacuum rated or it could collapse and cause your gauge to give false readings.

So, once again:

Size doesn’t matter; it’s how you use it that counts.

robot808

Ok, looks like I'm good with the hose. Any other shortcuts into the cabin from the engine bay?

Also, thanks guys for the vacuum explanation.

Opelotus

What about through the body plug where the plastic vacuum line for the HVAC runs? It's under the plastic cowl that covers the wiper motor, enters approximately in between the HVAC box and steering column. IIRC there were two unused "ports" in mine that hadn't been poked through.

jpitman2

The thing with a vacuum line is that it should be rigid enough not to collapse as the pressure drops inside - note the wall thickness of rubber vacuum tubing. Not all tubing is suitable. Hydraulic hoses made for pressure are well known for internal delamination if used for vacuum.
jp 83 Euro S AT 54k

yardpro

darn.... i was late on this one....
i could have put my physics minor to use.... dag nabbit.....

ltoolio

So bumping up an old thread here out of curiosity.

There was a statement in the thread above that size doesn't matter going to the gauge, as that would just delay the response to the gauge. That I understand.

But does the "size doesn't matter" apply to the rest of the underhood components?

If not, why did the designers bother to have different sizes under the hood?

If so, would the difference between, say, a 6mm line and a 3mm line be so drastic as to affect performance or response?

All of the above questions are asked with the assumption that the vac lines are high quality/non-collapsable under expected load.

(and although this thread was created by the PO of my '82, it's not meant to question anything he did.....honestly just curious).

Wisconsin Joe

Go back and read post #9. For a "signal" application, volume through the hose doesn't matter, so a smaller hose will give quicker response (less volume of air is moved to generate the pressure change.
For other applications, there is a need for a volume of air to be moved. The "signal" pressure isn't as important as actually moving air (like the HVAC actuators or the C/C). So a larger hose is used.

As with everything else, form follows function. Or at least it should.