Vacuum Question

[mikester]

Since I have my 81 running and moving Im finding little bugs that have to be worked out. One is the lack of vacuum ports. Theres one on the manifold just under the back fuel bowl. Im using that one for the booster. I had to use a tight 90 degree fitting because it was very close to the bowl.
Ive only got 2 left and theyre both on the base of the carb. One on the right side and the other in the front under the bowl. Its a Holley 4150 750HP series.
I cant use a spacer under the Holley because of hood clearance.
I havent checked how much vacuum I have yet since I havent picked up a gauge. Thats going to happen tomorrow.
What do you guys use for the modulator ? What about the PCV ? Its like I dont have many choices.

 

[MrSony]

Nothing really needs vacuum cept the HVAC stuff, trans if its a th350 (or th400), cruise and the brake booster.

 

[79 USA 1]

Since I have my 81 running and moving Im finding little bugs that have to be worked out. One is the lack of vacuum ports. Theres one on the manifold just under the back fuel bowl. Im using that one for the booster. I had to use a tight 90 degree fitting because it was very close to the bowl.
Ive only got 2 left and theyre both on the base of the carb. One on the right side and the other in the front under the bowl. Its a Holley 4150 750HP series.
I cant use a spacer under the Holley because of hood clearance.
I havent checked how much vacuum I have yet since I havent picked up a gauge. Thats going to happen tomorrow.
What do you guys use for the modulator ? What about the PCV ? Its like I dont have many choices.

I have an Edelbrock RPM Air Gap on the 406 in my 79 Monte Carlo along with a 750 double pumper Holley. I have a shallow 90 in the manifold at the rear for the brake booster but I also drilled and brazed in a port for the vacuum modulator on the transmission into the shallow 90. The PCV port is on the base plate of the carb under the rear float bowl. I have a .75 spacer under the carb to allow space for the shallow 90 to fit. I have a drop base air cleaner and a slight modification to the inner hood structure for clearance.

1) Brake Booster 2) PCV hard line 3) Vacuum modular line for transmission


Not a great shot but I just removed part of the "Bat wing" brace for air cleaner clearance.

Overall height with the air cleaner.

 

[mikester]

I have an Edelbrock RPM Air Gap on the 406 in my 79 Monte Carlo along with a 750 double pumper Holley. I have a shallow 90 in the manifold at the rear for the brake booster but I also drilled and brazed in a port for the vacuum modulator on the transmission into the shallow 90. The PCV port is on the base plate of the carb under the rear float bowl. I have a .75 spacer under the carb to allow space for the shallow 90 to fit. I have a drop base air cleaner and a slight modification to the inner hood structure for clearance.

1) Brake Booster 2) PCV hard line 3) Vacuum modular line for transmission
View attachment 132910

Not a great shot but I just removed part of the "Bat wing" brace for air cleaner clearance.
View attachment 132911
Overall height with the air cleaner.
View attachment 132912

A big issue for me is the HP series carb doesnt have a port on the back like the 750 you have. I tried a spacer before I found the fitting for the manifold and it brought the air cleaner up way too high. I have a dropped base now and it looks like it will clear but I really dont want to cut the supports inside of my hood. I think Im screwed. Looks like my only option might be a pump.

 

[fleming442]

Or, hydroboost.....

 

[Pc3]

not sure if this applies to you !,have a high rise intake! I drilled the intake just under the carb gasket and ran my vacuum from there

 

[pontiacgp]

drill the Holley base for a vacuum port

 

[mikester]

drill the Holley base for a vacuum port

I would drill the manifold before the carb base. That Holley new is $745. I would be really bummed if I screwed that up.

 

[pontiacgp]

I would drill the manifold before the carb base. That Holley new is $745. I would be really bummed if I screwed that up.

drilling the manifold would require the removal of the manifold to remove metal shavings so they do not end up in the engine. Drilling the base is common and you'll find many threads online about that.

 

[mikester]

drilling the manifold would require the removal of the manifold to remove metal shavings so they do not end up in the engine. Drilling the base is common and you'll find many threads online about that.

These two G bodys are the only cars Ive put together that have automatics. That being said, Im not 100% sure about what goes where as far as vacuum lines. Correct me if Im wrong. Booster is manifold vacuum and Ive got that hooked up to a 90 degree fitting screwed into the manifold under the rear fuel bowl. The base of the 4150 has two small fittings. Im assuming one would be for the vacuum advance but I have a mechanical advance distributor. Im capping both of those.
My thought is putting a tee on the fitting from the manifold and splitting it between the booster and the PCV. Then drill a small hole in the side of the intake just below the carb on the right side, stick a fitting there and use that for the modulator. Sound right ?