Manifold/Ported Vaccuum Question

[Rapid Roy]

This is a hypothetical question for general information and because I just don't know for sure.

1. Can the brake booster and PCV valve be ran off of carburetor from one port (with a T) and function correctly?
2. Can distributor advance and fuel charcoal canister be ran off of carburetor from one port (with a T) and function correctly?

This may sound strange, but it's something I thought about.

[Dr_Snooz]

Yes. However, if you put something on ported vac that should be on manifold vac, then no.

[SkinnyG]

^^^ yes.

All the vacuum comes from the same place, so a T is just sharing the course vacuum.

Pay attention to what is "PORTED" vacuum, and what is "MANIFOLD" vacuum.  Most things cannot be swapped around.

Brake booster and PCV are full manifold.

EGR and EVAP are ported.

Vacuum Advance can be either.

[Irish_Alley]

like they stated
pcv and booster should be the bigger hoses

vac advance should be manifold, unless you want better emissions then go ported.

egr IDK dont run one but one would assume it would be ported
evap again IDK but i would think you would want that manifold.

im going to say to wait till BD, Vile, Capt, hatzie or Rich chime in (might be a few others but thats all i can think of right now). 

[bd]

The information contained in this thread is incomplete, making it a little misleading.  A notable potential problem that can result from splicing multiple vacuum lines together is the limitation to vacuum recovery presented by the cross sectional area and length of the primary vacuum line.  If too many lines are joined together, vacuum demand can exceed the plumbing’s effective capacity and interfere with vacuum supply to the connected appliances that said appliances require for proper function.  Although the vacuum source may not be overburdened, the connected plumbing can be.  An analogy is too many sprinkler heads connected to a valve.  Once valve capacity is surpassed by demand, line pressure drops and water distribution from the heads decreases.  The result is a dead lawn.

Vacuum circuits can be categorized under two basic functions.  The first function is to continuously purge a connected device through ongoing depletion.  An example is the PCV valve, which is really just a calibrated vacuum leak.  Vacuum has to be continuously applied to the valve to compensate for inflow to the valve from the crankcase.  Another example is the purge line connected to the evap canister, which purges accumulated vapor from a tank that is open to atmosphere.  The second function of vacuum circuits is to either modulate or maintain constant vacuum in an otherwise sealed system.  Examples are the evap canister purge valve connected to ported vacuum, the distributor vacuum advance canister and the automatic transmission vacuum modulator valve.  The brake vacuum booster is a unique hybrid between the two types of circuits.  The booster is a vacuum motor that, at rest, exists as a closed system vacuum reservoir.  Vacuum drawn on the booster is maintained by the vacuum check valve indefinitely.  Then, when the driver depresses the brake pedal, vacuum is used by the booster and lost as it assists the application of the brakes by moving the master cylinder pistons.  When the brake pedal is subsequently released, the booster reservoir evacuates through its vacuum connection to manifold and restores the vacuum that was used.  Another example of a hybrid type circuit is the HVAC vacuum reservoir, which traps constant vacuum until used by the various vacuum motors under the dash and then recharges.

• Brake Vacuum Booster - uses 11/32", textile reinforced, stiff-wall EPDM rubber hose that meets SAE J1403 Type L and DOT FMVSS 106 requirements.  The brake vacuum booster is a major safety component plumbed directly to manifold vacuum.  It does not share it’s plumbing with any other device.  It relies on dedicated vacuum plumbing to prevent booster contamination and/or coking of the vacuum hose with carbon or fuel condensates, as well as prevent vacuum starvation of the booster that may result from unwanted influence by a connected appliance.
  
  
• PCV Valve - uses 3/8" textile reinforced vacuum hose connected directly to manifold vacuum.  The PCV hose often shoulders the extra burden of the evap canister 1/4" purge line.
  
  
• Evap Canister - the answer is specific to the vehicle year and which lines you’re questioning.  Depending on the year, the evap canister has a 5/16" fuel tank vent line, a 3/8" carburetor bowl vent line, a 1/4" purge line connected to manifold vacuum and at minimum, one 5/32" ported vacuum line.  It also has a vent port open to atmosphere.  The 1/4" manifold vacuum line can share the 3/8" PCV valve vacuum hose through an inline tee or vacuum tree integral with the PCV valve.

Generally speaking, OE vacuum lines that share a common vacuum source, whether ported or manifold, do so by connecting directly to the vacuum source independently, or through multi-branch "tree" fittings.  In addition, depending on the volume of flow through a vacuum line, engineers try to distribute the leaning effect of high flow circuits across all cylinders.  That's why the larger lines from the brake vacuum booster and PCV valve plumb to the base of the throttle plate rather than into an individual runner.  Then, of course, not all ported vacuum sources are timed the same; some open sooner than others providing different vacuum rates.  As to the original question, timed vacuum ports for the distributor vacuum advance and evap canister purge valve signal can be combined with no appreciable loss of function.

So, before pairing vacuum lines, consider the possible ramifications and use good judgment.