vetteguy75

I just installed a new Holley 4160 600cfm carb and it has only 1 large vacuum port in the back of the carb base (not 2 like the other Holley I had), 1 small vacuum port in the front of the carb base, and the vacuum port for the dist advance. If I connect the brake booster vacuum line to the large port, where would I connect the PCV line? Would the small vacuum port in front be enough? If not, what symptoms would I experience?

7T1vette

I think I would try the small port and see how it worked. If you find that you get some residual gas odor or oil fumes in the engine compartment, research how to make it larger or if you can join the brake booster and the PCV at the rear connection.

PeteZO6

On my 4150 Holley, the large port on the back is for the PCV. The small port on the front is for the distributor vacuum - the port on the right side is ported distributor vacuum which you don't want to use unless you have a smog motor. You should have a dedicated vacuum port on the intake manifold for the brake booster and other car vacuum needs like headlight and heater operation.
Cheers,
Pete

Dantana

11Jake

Thanks for the thread Vetteguy75, I have the same carb but it is a 750cfm holley 4160 and have the same issues I am working out.

vetteguy75

Here's the configuration I came up with....

1. Brake Booster to the 1 large vacuum port at the base of the carb.

2. The headlight vacuum line to the full vacuum port in front of the carb.

3. Vacuum advance line to the ported vacuum nipple in the carb's metering block.

4. I purchased a 2 prong vacuum connector (with threads) and screwed it into the intake manifold. Connected the transmission vacuum line AND the PCV line. That's why I wanted to know if the location of the PCV is critical. Right now it's located on the driver's side, front and the 2 prong connector is located at the rear of the intake. Ergo, I have to run a vacuum line from the front driver's side, around the carb and to the rear of the intake. Can you swap the breather and the PCV locations and run a short vacuum line to the manifold vacuum port?

So far this configuration seems to work....

PeteZO6

Vetteguy75,
I think the PCV should go to the base of the carb instead of the intake manifold because the PCV "port" on the carb connects to both sides of the intake manifold. The port on the manifold itself is tapped into only one side (assuming you have a 180° manifold), so if you put the PVC there the crankcase fumes are being pulled into only 4 cylinders, not all eight. Probably makes no big difference, but the General did it the way they did for some reason.

The PCV can go on either the driver or passenger side valve cover, as long as the breather from the air filter housing is connected to the other valve cover so fresh air goes completely through the engine. The General always seems to put the breather to the air filter at the opposite end as the PCV, that is PCV front, breather rear.

The instruction sheet that came with my Holley 4150 says to use the rear port for the PVC as in, "Connect PVC here" with an arrow going to the port in the photo.

Cheers,
Pete

enkeivette

Needs to be on manifold vacuum, not ported. Doesn't matter if you use the large port, but I like to keep that one reserved for the booster.