[Bermudagto]

I can’t locate any lower manifold inlet ports on this new Campbell Holley Carb!
Do I have to resort to a gas cannister instead?
I also need to tap vacuum for TH400.
Using the rear intake inlet for brake booster vacuum.
Can I use a splitter off of rear Intake inlet for BOTH brake and Transmission vacuum?

[SRGN]

Some Holley base plates have the bosses for vacuum fittings machined but not drilled. Look at the base of the carb, you may need to drill/tap and add screw in fittings.

[Bermudagto]

Well there are 2 stamped circles on the lower front of carb. I’m supposed to drill one out and add threads to it for a vacuum inlet? Holy S..t that looks difficult. See pic
Oh my carb is an Ultra XP Campbell 4150 so I just read those don’t always come with any vacuum ports. Hopefully I can just use the main port in my Intake for everything? Brakes/PCV/Transmission vacuum ?

[SRGN]

Ok, that's a "race" baseplate. You can run a carb spacer and drill/tap any ports you need, but I'd recommend not teeing off the brake booster line.

[NeighborsComplaint]

Yes, that’s a no-no. The brake booster vacuum is always a dedicated connection.

[Kenth]

Not being able to share a vacuum connection for the PCV and brake booster must be one of the longer myths.
Think for a moment about where the vacuum comes from.
Exactly, from a source under the carburetor's throttle blades, so there is no difference between the vacuum for both functions, the vacuum is taken from the same place.
Then there are those who are afraid that vapors from the PCV would find their way into the brake booster if you connect the hoses to the same port.
This is a waste of thought, it doesn't matter if the vacuum for the brake booster is taken from a T-fitting on the PCV hose or a separate connection under the throttle blades, the vapors are there too before they go to the cylinders for combustion.
And then, not least, the engineers have already solved the problem of vapors finding their way into the brake booster by having the brake booster use a check valve.
So it's mostly for practical reasons that the PCV and brake booster have their own ports in the design, some engines actually uses a shared port from factory for this.

HTH

[steve25]

Thumbs up to the above !

Full manifold is full manifold vacuum , but with a duel plane intake with no carb spacer you must take the vacuum off the carb since that’s the only passage that will link both high and low plenums to provide you with FULL manifold vacuum.

Do not dump the pcv valve into a vacuum port that your intake might have that only goes into 1 runner, as that’s not full manifold vacuum.

I have seen that too many times to count.

[HWYSTR455]

Those 2 lower stamped circles are in the bowl, and are for jet access without having to take the bowl off. Why they are not slotted for a screwdriver or have some other type of method for R&R is beyond me.

Yes you can T off the booster port, and just as a comment, common recommendation is to make it as close to the carb/port as possible.

Not sure why that's recommended, but felt I should mention it.

Note that an intake runner fitting is 'generally' acceptable, but could potentially see 'pulses'.

Note that if a trans vac module fails/leaks, it could potentially take out the booster diaphragm.

I forget where OE pulls vacuum for trans but 'think' it was from a runner. This might be due to the risk of the booster diaphragm contamination.

I'm still at 1 cup of coffee, so be gentle w me! Heheh!


.

[Goatracer1]

Some of the older Pontiacs had a vacuum fitting off the back of the carb that had 4-5 connections. The big one was for brake booster, medium sized one was for trans and the smaller ones for different items that required vacuum. If the factory can do it so can you.