Power Brake Vacuum

My carb has a vacuum fitting under the secondaries on the base that seems to work well http://www.panteraplace.com/Te...arb%20112101%207.jpg It can be seen just under the dip stick. My vacuum at idle is only around 11 to 12 inches. My PCV in connected to one of the ports on the intake.


Mike

Thanks for the reply.

Im a little concerned with using the manifold ports because they are each located right in a runner. Other manifold vacuum ports seem to be in a more central location. I called the Edelbrock help line for help. The tech said it would be OK to just use one of the ports; but he didn't seem really concerned with his job or my car.

I don't have a very good grasp of how much vacuum is used for these accessories or how much effect it has on the engine. I was thinking the PCV is always flowing so it would be more drain on the overall vacuum than the brakes that are more of a closed system. With that in mind I would use the carburetor source for the PCV and the manifold runner port for the brakes, or maybe even connect both manifold sources together to run the brakes so I would be drawing on two runners instead of just one.

My old intake was a tall single plane, I think probably Ford SVO (not sure it has been polished.) It had two ports tapped just below the carburetor for PCV and brakes. When I replaced the C302b heads I had to replace the intake thats when the issue came up. I really hoped to have the car on the street yet this year but its not looking good.

Is this a single plane or dual plane manifold? In a single plane (open plenum) the pressure is going to be about the same, so it shouldn't make much difference where you pull vacuum from. In a dual plane you'll want to pull equally from either side.

Typical vacuum for street use is 17 inches, but you can get away with less or put an accumulator in to help.

Question is why have you removed the C302B heads, they are some of the best heads you can put on a Cleveland?

Julian

The new intake is an RPM Air-gap dual-plane. The available vacuum ports are on cylinder 5 and 8 both on the same plane.

I removed the c302b because I was having problems with head gasket sealing properly. When we got the heads off we found I had blown a head gasket. The c302b heads need to be repaired, they have a crack at one of the head bolts that needs to be fixed. They were flowed and checked out ok otherwise but I didn't want to wait around to find someone that could properly repair the c302b's so I just got new heads. I will be selling the c302b's along with the intake and headers that fit them as soon as I get organized and take some pictures. They are pretty nice heads with titanium intake valves.

So back to the power brake vacuum. When you say I should pull equal from either side I assume you mean left and right. The current ports are front and back.

As another option can I just run a "T" connection off of the carburetor to run both PCV and power brakes. There are also two small vacuum sources on the carburetor but they are small and don't appear to be capable of handling PCV.

Call Demon for their recommendation for the power brake port and the PCV port. The power brake port needs to be a stand alone source. I've got an Edelbrock carb and the carb instructions are very specific about which carb ports to use for the power brakes and PCV.

OK; I contacted Barry Grant and they told me that they don't offer a carb with a port for PCV and power brakes and none of the other major carb makers offered two large vacuum ports on their carbs either. I don't think that is true but I have to research that a little more. They also said the ports on the intake "appear" to be for power brakes or other vacuum needs. However they said I should contact Edelbrock, which I have already done and got a less than reassuring answer. Since I am reluctent to drill another hole in my new intake and since I really don't know where the hole should be drilled since there are two separate areas to drill into, I guess I will use one of the ports on the intake runner and hope for the best. How bad could it really be other than burning up a brand new engine. Wish me luck.

quote:

I contacted Barry Grant and they told me that they don't offer a carb with a port for PCV and power brakes and none of the other major carb makers offered two large vacuum ports on their carbs either.

FWIW, I have a Holley 670 Street Avenger on my car and it has 1 timed (spark) port, 2 full vacuum ports, and 1 PCV port.
http://www.holley.com/0-80670.asp

Edelbrock carbs have 4 vacuum ports. A timed vacuum port, a manifold vacuum port, a PCV port and a power brake port. See figure 1 in the attached Installation Manual.

http://www.edelbrock.com/autom...nstall/1000/1801.pdf

I use a electrical vacuum pump from an Audi S5 in my pantera, with this upgrade you can save the line from the engine to the brake booster.
Pumps are around 80USD @ ebay.

cheers
Andy

FWIW, I use a large sheet metal Y-fitting and run both the PCV and the power brake vaccum hose off a single large hose bib to an SVO single plane intake. It seems that the 'flow' thru the vacuum connection is low enough that separate hoses for PCV and brake booster are unnecessary and in any case will ultimately connect to the same source- the intake plenum. I assume that a single large hose bib on other Holleys (my tuner double-pumper has no large connections at all) would work equally well. At any rate its worked this way on our car without a hitch since 1991....

Here is my setup. Luckily I can run the PCV to the carb base since it's a Holley. The break booster is to a 90 deg fitting in the intake as you described. Breaks seem to work just fine but I hope that a chanber is not running lean. I actually have not inspected the plugs since the rebuild about 1000K miles ago.

Thanks for the replies. I have run the pb vacuum with a 90 off the intake also. I'll worry about it later as I am just trying to get the car out of the garage right now. Thanks for everyones input.

I got the car started and Im only getting about 7 psi vacuum at idle right now, so I may need another vacuum source anyhow.

In your picture it looks like you also have a RPM air gap intake. Do you have issues with the air cleaner clearance on the deck lid?

quote:

I got the car started and I'm only getting about 7 psi vacuum at idle right now, so I may need another vacuum source anyhow.

If thats all the vaccum you get, there's either a serious vac leak somewhere, or you have installed a cam best used in NASCAR racing....

As for the possible intake/air cleaner interference, look at his photo: the engine cover as-stock is flat. That one appears sprung over 1". Nothing wrong with this, by the way.