SBC vacuum and alternator questions

[ryans69chevy]

I have a 78 Chevy 350 that I installed into my 67 Chevy 1/2 ton. It has HEI, a TH400, and a Holley 4160 vacuum secondaries. Vacuum is something I do not understand on engines so I am wondering what all needs vacuum and from where to where.

The only thing I have run is my heater core to my intake and heater core to my radiator.

I am also wondering if someone can tell me if this alternator has an internal regulator or needs an external unit? I've read a lot on how to tell the differences, which makes me think that this is an internal unit, but I just want to be sure. It came off a '73 Chevy big block - not sure if it is stock or not.

[Wrenchbender Ret]

You will need a vacuum tube back to the trans. modulator. It should have 1/4 in hose/tube. You need a vacuum hose to the vacuum advance canister on the dist. 3/16 hose. You can hook it to full manifold vacuum. Sometimes to get the best drivability you may have to hook it to a ported vacuum source on the carb.
That alt. is an internal regulated type.

[ryans69chevy]

Perfect! Thanks for the response!

What is the difference between ported and full vacuum? When would you use which?

What visually about the alternator told you it has an internal regulator so I know for future?

[geezer#99]

Ported is a vacuum source from above your throttle plates. Vacuum is only available from there when the throttle is open.
Full time vacuum is the vacuum your motor creates and is usually found below the throttle plates.
Full time vacuum can also be found in any opening to the inside of your intake. Usually you’ll find a port on the manifold behind the carb that is full time.

[rpmerf]

Vacuum lines on my 1970:
Vacuum Advance on the distributor. This is long debated as to whether it should go to a ported or manifold source. Leave it on the port it is on, otherwise you will have to re-time the engine.
Brake booster - Large hose to the booster
Transmission - Runs down the back pass side of the engine
HVAC - small hose goes in the cab on the pass side of the hump on the firewall
If you have a stock air cleaner, a vacuum line runs to that for the valve that switches between hot air or cooler air
I do not know what vacuum lines are required for your carb. My QuadraJet has one for the secondary valve.

The alternator is internally regulated. 10SI or 12SI (not sure the difference). There is a bunch of info on how to wire it up.

At least on my engine the hater core goes water pump -> heater core -> intake manifold coolant port

[ryans69chevy]

I'm having trouble with hooking up vacuum. My carb only has a tiny port sticking out of the primary bowl, which I found from research to be for an EGR system. I'm not sure if this is ported or full vacuum so for now I have it capped off. The carb doesn't have any other ports. The intake is an edelbrock performer with only one vacuum port on it.

I have to hook up my th400, distributor, and my PCV. How do I do all this from my setup? I've read that the transmission and distributor needs ported vacuum and the PCV should run into the carb. Right now I have everything running into the full vacuum port on my intake which has a "tree" screwed in.

I just had this engine rebuilt.

[geezer#99]

Exactly which Holley do you have?
Pics would help.
Most have several ports.
You need manifold vac for your tranny.
That port on the metering block(bowl) is ported.
Do you still have an egr?

[ryans69chevy]

It's a 4160 with manual choke. I will grab some pics of it tonight. I am not using an EGR system. Every Holley I've seen has like you said more than one vacuum port. I cannot find any besides the EGR. Not even on the back normally where people run their PCV.

I figured out that my tranny needs full vacuum. So I just need help figuring out where the distributor vacuum goes and where the PCV goes. I read that the PCV should have its own vacuum port so the other items don't get dirty. I've also read mixed reviews about dizzy vacuum - some say ported some say full. I'll get pics tonight. What all would you like to see? Do you need the casting numbers off the Holley?

[geezer#99]

Pics front, back, both sides will do. Carb list number optional.
You have the option of a spacer under the carb that has vacuum taps on it if you need to.

[ryans69chevy]

Okay will do. Yea I have a spacer, but it doesn't have any ports drilled in it. Maybe it would be smarter to buy one with it in the spacer. Probably less of a headache.

[geezer#99]

Take pics. I’m curious what you have.
You can always drill some ports into a spacer if needed.

[ryans69chevy]

Pic 1

[ryans69chevy]

Pic 2

[ryans69chevy]

Pic 3

[ryans69chevy]

Pic 4

[ryans69chevy]

I will change out the rubber fuel line to braided line soon. I don't have the mr. gasket spacer under the carb installed either.

[geezer#99]

Interesting!
Did you get a list number off it?
Might be a tunnel ram carb.

[Captainfab]

That's an old Holley. Likely either a 1850, 1850-1 or one of the factory carbs from the '60's such as the 2818. Those early carbs did not have provisions for a PCV valve since they were not used back in those days of the road draft systems on the small blocks. That port on the primary metering block is ported vacuum and can be used for the vacuum advance on your distributor. As for connection for a PCV hose, a spacer plate with the port will be the simplest solution.