[Nutro]

Any Vortec guys in here? I'm embarrassed to admit, I haven't messed with SBC stuff in a while and it's been 25 years since I've owned a car with a carburetor.

I picked up an old Firebird Formula and it has a "Stage 2" L31 Vortec 350 with a quick fuel 680cfm carb.

It only has 1 large (3/8) vacuum nipple and it's routed to the brake booster.

There are 2 small nipples on front passenger side of carb. One is spark controlled and one in manifold vacuum?

There is a PCV valve in the passenger valve cover and it's just venting to atmosphere at the moment. I don't know it the PCV is needed? I would assume so, but there is no provision to hook it up to. I also need a small vacuum source for the HVAC system but I can't see where it could go as well.

There is a port in the back of the intake that I COULD get vacuum from, but the dang carb blocks putting any kind of fitting in it. There is maybe 5/8" gap between intake and carb base.

So, I have these items that need vacuum:

3/8 Brake booster hose
TH350 vacuum modulator
HVAC controls
Distributor advance
PCV (needed)?

[Schurkey]

ANY vehicle run primarily at part-throttle needs PCV and vacuum advance. Venting crankcase fumes to atmosphere is just TOTALLY irresponsible.

Edelbrock sells a low-profile 90 degree elbow that's useful for vacuum ports too close to the carburetor. This is what I could find in a quick search, you probably want something similar but 3/8 NPT male by 1/4 or 3/8 NPT female.
https://www.summitracing.com/parts/edl-8096


Put the power booster on a vacuum port that goes directly into a manifold runner. Route the PCV to a vacuum port where the fumes stand a chance of being distributed to all eight cylinders--a port into the plenum. IDEALLY this is a port on the front of the carb where the fumes can mix nicely with the incoming fuel/air stream on the primary side, but some doofus carb engineers don't provide a suitable port like that. In which case, you're kinda locked-into using a port on the rear of the carb. The PCV hose should not be teed-into any other vacuum system--needs to go directly to the plenum, or a port on the carb that leads to the plenum. The PCV system is a controlled vacuum leak, so the vacuum in that hose is unsuitable for trans modulators, vacuum advance, brake booster, etc.

IF (big IF) the casting has an undrilled boss on the front, you can drill it yourself, poke a 3/8 steel tube in there, sealed with Loctite thread locker, and with a small bead formed on the end to hold the vacuum hose.

[77 TRASHCAN]

There is no down side to using a vacuum advance. It provides more advance at lower engine loads, and lessens as you give the engine more throttle. Better MPG, better driving!!!

Engine longevity started getting much better for all makes in the 50's when a system was designed to burn the acrid oil vapors formed in the crankcase in internal combustion engines. As mentioned, it is a controlled vacuum leak. Engines without PCV systems had all kinds of problems. The oil would turn acidic from the combustion gases that got in the crankcase. Every part in the crankcase suffered as a consequence...
Many modern vehicles don't have a visible PCV valve, but do have a way to perform that function...

[77 TRASHCAN]

There is no down side to using a vacuum advance. It provides more advance at lower engine loads, and lessens as you give the engine more throttle. Better MPG, better driving!!!

Engine longevity started getting much better for all makes in the 50's when a system was designed to burn the acrid oil vapors formed in the crankcase in internal combustion engines. As mentioned, it is a controlled vacuum leak. Engines without PCV systems had all kinds of problems. The oil would turn acidic from the combustion gases that got in the crankcase. Every part in the crankcase suffered as a consequence...
Many modern vehicles don't have a visible PCV valve, but do have a way to perform that function...

[Nutro]

Originally Posted by Schurkey

ANY vehicle run primarily at part-throttle needs PCV and vacuum advance. Venting crankcase fumes to atmosphere is just TOTALLY irresponsible.

Edelbrock sells a low-profile 90 degree elbow that's useful for vacuum ports too close to the carburetor. This is what I could find in a quick search, you probably want something similar but 3/8 NPT male by 1/4 or 3/8 NPT female.
https://www.summitracing.com/parts/edl-8096


Put the power booster on a vacuum port that goes directly into a manifold runner. Route the PCV to a vacuum port where the fumes stand a chance of being distributed to all eight cylinders--a port into the plenum. IDEALLY this is a port on the front of the carb where the fumes can mix nicely with the incoming fuel/air stream on the primary side, but some doofus carb engineers don't provide a suitable port like that. In which case, you're kinda locked-into using a port on the rear of the carb. The PCV hose should not be teed-into any other vacuum system--needs to go directly to the plenum, or a port on the carb that leads to the plenum. The PCV system is a controlled vacuum leak, so the vacuum in that hose is unsuitable for trans modulators, vacuum advance, brake booster, etc.

IF (big IF) the casting has an undrilled boss on the front, you can drill it yourself, poke a 3/8 steel tube in there, sealed with Loctite thread locker, and with a small bead formed on the end to hold the vacuum hose.

Yep, I'd definitely want to run the PCV. I saw that Edelbrock fitting but it shows it's 7/8" tall and I read all of those reviews on Summit and they all say their carbs would not fit with that fitting. I can run a 1/2" spacer but now hood clearance becomes an issue

[NeighborsComplaint]

Try a power steering return line fitting on the rear baseplate port for the vacuum booster.