Which ports on carb?

[Faster Eddie]

Guys, my 1406 Edelbrock carb has 2 vacuum advance ports. One for emissions controlled and one for non.

Is there a performance difference?

Also, should my brake booster be hooked up the port in back of the carb or just manifold vacuum?

 

[JAFO]

Not sure on the 2 vacuum ports, but the brake booster wants manifold vacuum. If the port on the carb is supplying that it should be fine. My Holley carb had a port in back that is manifold vacuum and I ran the PCV to that and I just used one of the threaded holes in the Edelbrock intake for the booster vacuum.

 

[bwyman]

its better to run the PCV to the manifold and the brakes to the carb. Plug the ported vacuum port on the carb. I can see you have a mechanical advance dist. only.

 

[Faster Eddie]

That's not my set up as described above, but why is it better for the brakes to be in carb and Pcv to be in manifold?

Also, any insight on the differences in ports for the emissions vs non emissions controlled engine?

 

[JAFO]

Yeah, x2 on that. Why is it better to have the booster to the carb?

 

[DirtDonk]

its better to run the PCV to the manifold and the brakes to the carb...

Hey bwyman, welcome to cb.com!!
Actually, while it might work ok, it's not necessarily better to do it like you state. As long as the PCV is connected to the intake manifold PLENUM and not an individual runner, you're fine connecting to the manifold. But you should never connect it to an individual runner because it's drawing too much air/fumes/crap into one cylinder only and messes with the mixture and balance.

For the brake booster, that's fine as it's not constantly allowing more air in unless there's a break in the diaphragm.

Most intake manifolds that I've seen only have a vacuum port in the individual runner (usually number 8 I think) but some have one in the common area too.
The Edelbrock carbs I'm familiar with have two properly sized ports for your 3/8" line however, so you could run hose barbs in both and run the PCV from one and the booster from the other.
Or you could use the one in the carb base for the PCV and the one in the back of the intake for the booster. Whichever is more convenient.

Never seen a factory PCV plumbed into just one runner on any engine. There might be some out there, I've just never seen one. Boosters are run that way all the time though.

Faster Eddie, like bwyman said, just plug the two little ports. Unless you're going to change over to a vacuum advance distributor, you don't need either unless you have other things that need to be connected to vacuum.
If you have other things, such as an auto trans modulator, you can either connect it to the full vacuum port on the carb, or better yet get a "vacuum tree" device to connect it and the booster to.
Vacuum trees are just multi-port manifolds to connect more than one device to a single location on the manifold. If you don't have any other devices, just plug the fittings on the carb.

Oh, and because I can't leave a sleeping dog lie, you might consider making your own caps out of hose or something. Or else get some from a dealer or junkyard off of a newer car. The vacuum caps you buy at the store these days are crap. Unless they've changed in the last year or so, you'll be lucky to get six months out of them before you start chasing vacuum leaks.

Paul

 

[Faster Eddie]

I am running an HEI dizzy, which has a vacuum advance on it. Which port should I put it on? Emissions (pass side front of carb and higher of the two) or non Emissions (driver side and lower than the other).

 

[Faster Eddie]

 

[Faster Eddie]

Is there a performance difference between the two?

 

[DirtDonk]

I would definitely start with the higher "ported" or timed vacuum fitting. This is how "most" EB's run best.
I say that tentatively though, as many here have found their sweet spot with the lower full manifold vacuum port. But many more of us prefer the ported.

Whenever in doubt as to which is which (in case height is not a good indicator) the ported fitting will not have any vacuum signal at idle. While the non-ported full manifold vacuum one will.

Paul

 

[DirtDonk]

There is a distinct difference in how an engine runs between the two.
Which is best will only let itself be known once you try them.

I always set the base timing, then use the timed port to see how it runs. So far I've only had one car (a '66 Corvette) that liked full vacuum most of the time. It would run decent on either, but seemed to like full vaccum more.
None of the Fords I've ever worked on with a single port vacuum advance liked full vacuum. But as said, several members here prefer it and may pop in to give their experiences.

Paul

 

[JAFO]

DirtDonk, the pic is of my engine. You will laugh, but I have mechanical advance because I never took the dizzy out of the box for seven years. I bought the Bronco in 2007 not knowing what I had bought. Thought I was just going to do mechanical stuff and bought a new engine, dizzy, carb, etc. Found rust and lots of it. Shelved parts I had bought for the new engine and started full bore on the body. Anyway, by the time I finished the body and chassis restore seven years had passed. I pull the dizzy out of the box and I am like WTF, I thought I had a vacuum dizzy. Nope and no way to do any return. But the motor seems to run very nice and gas mileage is surprisingly good.

 

[jckkys]

The Edelbrock diagram is misleading. Most AFBs only have one vacuum advance port. The AFB was designed by Carter who made them for many years as OE on Fords, GMs and Mopars. Later ones were made by Webber who makes the AFBs sold by Edelbrock. The timed vacuum port is the one to use on Ford SBs weather emission ie. later model or pre-emissions. Most carbs only have a timed vacuum port. The PVC port is correct unless the carb spacer has one. You want the PVC gasses to enter the A/F mixture just below the primary throttle plates, so it's distributed equally to all cylinders. The power brake booster is best sourced at a vacuum tree in the intake behind the carb. That's how Ford made all V8s with power brakes. No reason to change it.

 

[Faster Eddie]

Thx jckkys that's exactly the way I have things now

 

[Broncobowsher]

The ported vacuum goes to the distributor vacuum advance. By using ported instead of full vacuum the engine has less timing at idle. This tends to help the engine take a load without a large change in RPM. Automatics go into gear with less RPM drop, alternators don't pull the RPM down as much under load, stuff like that. Still get some drop, just usually not as dramatic with ported vacuum.

PCV should go to the base of the carb. It is pretty much a steady flow and you want to distribute that among as many cylinders as possible. Putting that into a single runner can alter how that one cylinder fires compared to the other 7.

Power brakes can go just about anywhere. There isn't any real flow. Just a little puff as the booster gets sucked down to a vacuum and after that it just sits there not flowing anything. I prefer a runner as the intake pulses therotically can create a touch more vacuum as they are pulling air out of the common plenum.

 

[bwyman]

Hey DirtDonk you are correct in what you are saying you can use manifold or the carb for you brake booster. Having been in the performance after market ignition business for ever my contacts at Holley & Edelbrock say connect the brakes to the carb. Just a quick note on vacuum advance. For best results the vacuum advance should be connected to ported or timed vacuum fitting. Vacuum advance is an economy function only. When the vacuum is up it adds more timing to the engine.

 

[jckkys]

The vast majority of Holley 4150/4160s have no vacuum port for power brake boosters. Only recent incarnations and double pumpers have a 3/8" nipple in the rear. As stated tho, any full intake vacuum source will work. The intake port is already there and you don't need to touch it when you pull the carb.

 

[Faster Eddie]

Thanks everyone.

 

[patterdale]

I am running an HEI dizzy, which has a vacuum advance on it. Which port should I put it on? Emissions (pass side front of carb and higher of the two) or non Emissions (driver side and lower than the other).

You keep saying emissions. One is ported vacuum and the other is manifold vacuum. The ported goes to the vacuum advance and the manifold vacuum is to run vacuum powered accessories. Heater doors etc. Ported increases with rpm and manifold is relatively constant. Hook your distributor to the one that sucks harder with rpm increase.

 

[Faster Eddie]

I was merely quoting the picture.