Author Topic: Cobra weber intake  (Read 5822 times)

zray

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Re: Cobra weber intake
« Reply #45 on: March 16, 2018, 11:05:21 AM »
Have seen a Weber manifold with stainless hard lines connected to a fitting drilled in each runner just below each stack. All eight lines ran to a block with a single vacuum port. Would that be adequate for power brakes? Where would PCV be plumbed to?


I've seen those too.. Too many connections to have potential vacuum  leaks, and too much complexity for my tastes. I don't think you are going to have enough combined vacuum to operate both power brakes and have a PCV system with a decent vacuum. I only had 10" of vacuum, and that was on a relatively fresh overhaul.

If you have to have power brakes, I think you are going to need some type vacuum pump, either electric or engine driven.


Z

JD

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Re: Cobra weber intake
« Reply #46 on: March 16, 2018, 11:18:07 AM »
Have seen a Weber manifold with stainless hard lines connected to a fitting drilled in each runner just below each stack. All eight lines ran to a block with a single vacuum port. Would that be adequate for power brakes? Where would PCV be plumbed to?

for a visual reference (there may be others) ...
'67 Shelby Headlight Bucket Grommets https://www.saacforum.com/index.php?topic=254.0
'67 Shelby Lower Grille Edge Protective Strip https://www.saacforum.com/index.php?topic=1237.0

mygt350

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Re: Cobra weber intake
« Reply #47 on: March 16, 2018, 11:42:02 AM »
Look like those are hose barbs. One I saw had stainless hard lines to each port. Was really interesting to see how each tube was bent to not collide with any of the others. Lots of connections that could cause a vacuum leak though.
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shelbydoug

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Re: Cobra weber intake
« Reply #48 on: March 16, 2018, 12:40:42 PM »
Have seen a Weber manifold with stainless hard lines connected to a fitting drilled in each runner just below each stack. All eight lines ran to a block with a single vacuum port. Would that be adequate for power brakes? Where would PCV be plumbed to?

You mean like this? That's my set up initially. It's a little different now on the car.

 Now this is how it is plumbed for my Pantera and the car has different space considerations for things like the vacuum manifold, i.e., where things are located and how is because of the access to them. On a "Mustang" where you would put things and even the way the linkage is done varies. The Pantera has very specific requirements to make things work.

In my case, there isn't enough volume of vacuum to operated the Pantera power brake booster. It is possible, even likely that different power booster require different volumes? That I never played with.

When the Webers were in my Shelby I ran manual brakes with the big 1-1/4" bore master cylinder.


On the air filters, it doesn't matter where the element is, it will get soaked with atomized fuel.

There are other engine configurations that do not create a push back through the intake ports.

6 cylinders do not, 4 cylinders do not. I don't know about 12 cylinder engines like Ferarri's. So what the issue is of blow back is the normal camshaft design for an 8 cylinder engine.



You can run the 46IDA-3 on the Porsche 6 cylinder, the Corvair that has been converted to the Porsche design, use two 48IDA's on a 4cylinder VW dune buggy. NONE of them have an "overlapping cam design" so none of them pressurize the intake port causing the blow back.

The simplest way to fix this on any V8 is to go to the Weber look alike fuel injection throttle bodies. Then since there is no atomized fuel in suspension, there is no blowback AND you can run any kind of an air cleaner that you want.

The difference is that the carbs are a $3,500 swap. The FI is about a $5,500 swap because of the computer and other electronics needed.



My information tends to agree with what Z is saying but I have only run them on my 351's. The horsepower loss over running open stacks  vs. air filters is 80 to 100hp LOST with air cleaners. That's about what you gain by adding the carbs to begin with.

IF all things were exactly equal, you can clearly show this on an engine dyno. A single Holley 4179, 750cfm, double pumper carb will clearly show around 80 hp less then the Webers on the exact same engine. But you get into variables as well.

As Jim Cowles just posted above, even the screens show about a 40hp loss over open stacks, but you need them to keep the squirrels from getting sucked in.

For instance this particular engine makes another 80 hp with 2" primary tube, 180 degree headers over the 1-3/4" dyno headers. In a Pantera you can fit those headers. In a "Mustang", you can't.

So just because of the different chassis the same engine is in you can use the taller 5" velocity stacks and the bigger headers. That's around 100 hp more then you can get with the same engine in the "Mustang" because of the limitations.

So, all things aren't equal.


OH, and just so the Cobra guys don't feel left out, "it was said" (not by me and I don't know exactly who) that the GT40's with virtually the same engine as the race Cobras, made 100 hp more because of the headers (bundle of snakes).


I don't know where my pictures are of the Boss 351 with the Webers in my 68 GT350 are right now. Those are circa 1978-9.
That set up was a little different BUT you can still NOW see the charred marks on the bottom of the hood from the Webers from start up. Particularly the front two stacks.

I remember Kopec hanging around until dark for me to start the car in the dark so he could take pictures of the flames coming out of the carbs that you don't see in the light. Leave it to him. I wonder if he can find those?


I had a nice video of an engine on the dyno. An iron head 357 with Webers making 600 hp @ 6500, 500 lb-ft @ 5,000, and it showed the vapor hovering like clouds just over the top of the 3-1/2" stacks that were on the carbs. That was as clear as it gets about the blowback. Put a 5" stack on them, the vapor stays in the stack.

Put a "Weber cam" in that engine, deduct 80hp.
« Last Edit: March 16, 2018, 01:27:17 PM by shelbydoug »
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mygt350

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Re: Cobra weber intake
« Reply #49 on: March 16, 2018, 01:02:34 PM »
Here is a pic of the Cobra Weber intake with hard vacuum lines to each port.
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mygt350

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Re: Cobra weber intake
« Reply #50 on: March 16, 2018, 01:12:28 PM »
The post by JD identifies 4 carbs. The 4th version with the tabs has date code of L8 which indicates Nov 78. Am looking at a 48IDA4 with the tabs and it has a "1F' date code. Does this indicate Jun 71? Were date codes always alpha/num, num/alpha or both?
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shelbydoug

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Re: Cobra weber intake
« Reply #51 on: March 16, 2018, 01:15:04 PM »
Here is a pic of the Cobra Weber intake with hard vacuum lines to each port.

On the Shelby you can do that. On the Pantera, the center valley is taken up by the linkage. My vacuum pick ups are on the exterior and go to a long vacuum manifold tucked in behind the header heat shield.
« Last Edit: March 21, 2018, 08:00:56 AM by shelbydoug »
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shelbydoug

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Re: Cobra weber intake
« Reply #52 on: March 16, 2018, 01:17:31 PM »
The post by JD identifies 4 carbs. The 4th version with the tabs has date code of L8 which indicates Nov 78. Am looking at a 48IDA4 with the tabs and it has a "1F' date code. Does this indicate Jun 71? Were date codes always alpha/num, num/alpha or both?

You need to ask Dan Case. He's the expert on the date codes. To me the only significance is someone trying to get super premium money for what they call an "original" set obviously made in the '70s but supposedly original to the mid '60s.

Functionally they all work the same.
« Last Edit: March 21, 2018, 07:59:19 AM by shelbydoug »
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shelbydoug

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Re: Cobra weber intake
« Reply #53 on: March 21, 2018, 08:29:09 AM »
Here are the tall velocity stacks.

Here's the Compcams vacuum pump.
« Last Edit: March 21, 2018, 10:15:39 AM by shelbydoug »
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