Weber manifold vacuum

[PaulProe]

Has anyone added under manifold tubing to a Weber manifold? Any tips on drilling and hooking up? Is any special treatment needed on the fittings that thread into the runners?

Thanks

Paul

[Gaz64]

Unfortunately I don't have pics of my own at the moment.

I'm sure many have done this and would be willing to share pics.

I fitted 1/4 NPT to -4AN male adaptor fittings to the runners sealed with liquid thread sealer.

The rest was hard line plumbed with appropriate AN fittings which ended as a bulkhead fitting at the back of the manifold.

[bobcowan]

Use pipe threads, and seal with standard teflon sealant. Should make for a leak proof seal.

Here's the first manifold I used. I got rid of this one because the ports were too small.

[dallas_]

I didn't plumb this and it's not a very good photo, but hopefully you can see how this person did it. Maybe it will help a little bit.

[PaulProe]

Bob
Is there a reason you needed the extra reservoir? Power Brakes maybe seems like overkill for PCV and you can't use manifold vacuum for distributor advance

? ? ?

Paul

[Dimis]

Or you could contact eightstack...
I believe they have sought to "build in" or "mill in" their own solution.




Bottom plate seals to create a "plenum" to balance vacuum across all the runners.



Note the small holes (4 across the top of the pic) drilled out at the bottom of each of the runners.

Quite pretty, but I can't vouch for it.
I'm yet to use the product myself, but would consider it given the opportunity.

[bobcowan]

Originally Posted by PaulProe

Bob
Is there a reason you needed the extra reservoir?

With 8 individual vacuum lines, you tend to get some pulsing. Having a small reservoir like that eliminates that, and gives a cleaner signal. For power brakes, you would probably want something bigger.

Originally Posted by Dimis

Or you could contact eightstack...
I believe they have sought to "build in" or "mill in" their own solution.

I'm currently using a manifold like this one, with a large common plenum cast into the bottom, and a cover plate bolted on. I got it from Wayne Presley a few years ago. He tells me this manifold is no longer available.

[Dimis]

Originally Posted by bobcowan

I'm currently using a manifold like this one, with a large common plenum cast into the bottom, and a cover plate bolted on. I got it from Wayne Presley a few years ago. He tells me this manifold is no longer available.

Bob,

How has this style of manifold worked for you?

PS: Has it crossed your mind that perhaps there's a chance he could be mistaken? Or did he mean; that they are NOT available for him to access or use? Just saying.

[zrayr]

they are available from Jim Inglese. When he put together a weber system for me he used one of the plenum manifolds at my request.

Z.

[vector1]

just an observation, i had a vacuum gauge hooked up to a carb spacer using 1/8" tube out of the spacer hooked to rubber hose about 3' long to the gauge so i could read it while driving, there was a slight restriction in the carb spacer as i hadn't drilled all the way through for the piece of tubing and i couldn't get a reading. had to open it up.

makes me wonder if all the tubing you guys are using is large enough.

[CompClassics]

You have to have a plenum or reservoir that the pipes attach to, simply running pipes will not provide the vacuum signal needed.
Here is a photo of one that I fabricated for an XKE "Light Weight":

[zrayr]

Not too sure about that. I've seen a lot of guys that ran all the vacuum lines into one collector fitting, and they had plenty of vacuum signal to register on a gauge .

Z

[Gaz64]

Originally Posted by zrayr

Not too sure about that. I've seen a lot of guys that ran all the vacuum lines into one collector fitting, and they had plenty of vacuum signal to register on a gauge .

Z

+1.

Each cylinder contributes in turn to a "vacuum rail".

[CompClassics]

zrayr or Gaz64

Have either of you seen people that have to run external vacuum reservoirs because of vacuum being inadequate enough that they've had to resort to vacuum reservoirs and or external vacuum pumps to create the vacuum that their vehicle needs?
Why would it be that even manufacturers that offer individual runner EFI systems build vacuum reservoirs into their manifolds, because they can afford to, engineer, design and manufacture something that is not necessary? I've used these systems on several different engines and can attest to simplification of tuning a individual runner system, wether it be a carbureted or EFI fuel system.
You can install a vacuum gauge on one cylinder and while the engine is running it should show a vacuum reading, is this amount of vacuum going to be enough vacuum to sustain what you are trying to accomplish? It's sort of like having a air compressor with a five gallon reservoir and trying to operate a tool that requires a minimum of a ten gallon reservoir, the air compactly is going to be insufficient to operate the tool properly.

[zrayr]

Originally Posted by CompClassics

zrayr or Gaz64

Have either of you seen people that have to run external vacuum reservoirs because of vacuum being inadequate enough that they've had to resort to vacuum reservoirs and or external vacuum pumps to create the vacuum that their vehicle needs? .......".

In the context of high performance engines that forum members are likely to be using in a Cobra or other lightweight high performance classic, people I know that had to have vacuum reservoirs and such, ONLY had to do so due to a radical cam that had too much overlap to allow for much manifold vacuum. That was only a concern when vacuum was needed for power brakes, steering, etc.

People that had the sense to do without power brakes & steering needed no vacuum reservoir.

My only "need" for a vacuum signal is because I like to have a vacuum gauge permanently installed.

Z.

[Gaz64]

Originally Posted by zrayr

In the context of high performance engines that forum members are likely to be using in a Cobra or other lightweight high performance classic, people I know that had to have vacuum reservoirs and such, ONLY had to do so due to a radical cam that had too much overlap to allow for much manifold vacuum. That was only a concern when vacuum was needed for power brakes, steering, etc.

People that had the sense to do without power brakes & steering needed no vacuum reservoir.

My only "need" for a vacuum signal is because I like to have a vacuum gauge permanently installed.

Z.

Agree.

The reason manufacturers of IR manifolds have an included hidden plenum to join all the runners together is it is easier and cheaper to cast it as part of the manifold. You can accomplish the same result with a Vacuum rail underneath if the manifold is not already equipped with a plenum.

As far as manifold vacuum operated accessories is concerned the plumbing mentioned above is more than adequate to supply power brakes, HVAC vacuum motors, a map sensor etc.

[bobcowan]

Originally Posted by Dimis

Bob,

How has this style of manifold worked for you?

PS: Has it crossed your mind that perhaps there's a chance he could be mistaken? Or did he mean; that they are NOT available for him to access or use? Just saying.

It works great. The only thing I use vacuum for is the MAP sensor for the EFI.

I'm telling you what Wayne told me.

[CompClassics]

Actually you guys are not getting the benefits of the vacuum reservoir at all, aside from providing benefits for operating accessories it is also a performance enhancement for Weber carburetors which is what this post was all about, hence if you can provide a better vacuum signal for the Weber carburetors in turn you can increase the profiles of the camshaft. Another thing to remember is is that it's not just vacuum, it's a mixture of fuel and air that is in the reservoir.

[zrayr]

I just don't see the science in the theory that you are proposing. The "mixture" in the reservoir does not contribute in any significant way to the mixture that goes down the throat of the Weber and into the cylinder head. Interesting discussion though.

Z.