[Carmine]

Hi everyone. I'm just about ready to start my motor but I do have some questions about vacuum lines. For the trans. vacuum line, I used the port in the front lower right section of the Q-Jet. For the distributor vacuum advance, I used a port on the fitting located in the lower rear of the carb. The fitting will also supply vacuum to the power brake booster. There is another vacuum fitting/port in the driver side lower front on the intake manifold, which I have a cap on. I believe that is all I need or have. I have a cap on the port for the power brakes. I'm going to check first the available vacuum before I hook up the line. I don't think I'm going to have enough vacuum for the brakes as is. How and where I have these lines hooked, does it sound ok??? I'll also attach pics. Thanks for looking and any advice, Carmine.

[Blued and Painted]

The trans modulator should connect to the plugged port above the choke pull off source. Heater control should connect to the small T off the brake booster source. The vacuum advance should connect to the small manifold vacuum source in front of the carb

[74Grandville]

Yeah the lower front port is for the evap. System. Just cap that one off.


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[TedRamAirII]

Does not look like your carb has source for ported vacuum for the Vacuum Advance, so Manifold Vacuum it gets.

[Kenth]

1970-74 Pontiac Quadrajets, except 455H.O./455S.D., do not have a timed/ported source for the ignition vacuum advance.
It may be added though.
Those years the TCS system were used to control the ignition vacuum advance.

[Carmine]

Originally Posted by TedRamAirII

Does not look like your carb has source for ported vacuum for the Vacuum Advance, so Manifold Vacuum it gets.

Thanks everyone, but I'm slightly confused. Let me explain what I read in these threads the way I understand it.

1-for my distributor vacuum advance, I am to use the port in the intake that I presently have capped off in pic #1.
2-for the trans. modulator vacuum, I'm to use the port on the carb. in pic #2 that I presently have a red cap on.
3-the heater vacuum line gets connected to where I presently have the dist. vacuum advance line.
4-the port on the base of the carb. in the front that I presently have my trans. mod. line to, will not be used and gets plugged.
Thanks for your patience, Carmine.

[steve25]

What will you be running for a air cleaner assembly?

[Carmine]

Originally Posted by steve25

What will you be running for a air cleaner assembly?

A stock dual snorkel air cleaner. I see 2 ports on them which I assume requires some form of vacuum?? I looked inside the snorkels and if memory serves me, there was some form of a flap?? Not sure where that vacuum would come from?? I don't have a strong interest in making them functional at this time. I'll just have to figure out how to keep the flaps open and cap the ports on the air cleaner. That's unless there is an easy fix for this??
You see, my problem is the previous owner really butchered the vacuum system and electric. He put on a Holley carb. and worked around that for everything. He either altered things or changed them completely. Even did some welding. I don't want to tell you what I found under the dash. I have parts that either had a vacuum line(s) going to them, unhooked-not working-or electric plugs that went to what I don't know.
Before I post any issue, I always try to resolve it myself before annoying and bothering anyone. I look in my repair manuals and also on line-You Tube. Unfortunately, every pic or schematic I saw re. vacuum lines, I couldn't tell either where they started or where they went. I never saw a complete pic that is why I asked here. I'm looking just to have everything that is needed for a good running engine, working properly. I know that vacuum is a part of this and that is where I'm at. I do thank everyone for their time and effort, Carmine. .

[Formulajones]

What you listed in post #6 will work just fine.

On the air cleaner, if you have no interest in making the heat riser work, then leaving those vacuum ports unplugged just leaves the flaps open all the time and will function fine that way.

[74Grandville]

I'm not sure I would use the port in the intake for the distributor as it is a pulse type signal. I would put a t on the back port and have both the heater and distributor connected to the full manifold port.


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[Holeshot71]

The vacuum controls in the dash tend to leak some, at least from what I've seen. With larger than factory cams and lower vacuum, the brakes need all the help they can get. If it was my car I would leave the vacuum advance where it is and connect the heater controls to the small port in front of the carb.

[Carmine]

Well guys and gals, the verdict is in. No matter where I tested for vacuum, I only had 10 inches. Disappointed yes. Surprised no. But, as the motor goes up in rpm's so does the vacuum. So, I do believe it is decision making time. It's either change the cam shaft or a vacuum pump. The power brakes are going to work one way or the other. That cam shaft has to be fairly radical. You don't see the engine shake much, but siting in the car, you certainly feel it. Standing behind the exhaust, definitely can tell it's not stock. Almost sounds like a little miss in it, but it's not. The engine seems to rev short and quick if that's the way to explain it. I bought this car to enjoy driving it asap. So, a cam removal is out of the question; at least for now. Perhaps over the Winter I might see it happening. That leaves me with a vacuum pump. I previously did some research on them just in case. Just in case has arrived. I can't recite the brand or name, but Summit sells one for about $250.00. It got real good reviews. Users remarked on how quiet it was. So, I have to ask, any members ever use one of these?? Which brand did you buy?? Were you happy with it?? Many thanks, Carmine.

[Squidward]

You can impact your vacuum greatly with carb tuning and timing. It sounds like your tune is not ideal if you are getting 10". What engine/cam, and what timing specs?

I run a vacuum tee off my carb base (manifold vacuum) to supply manifold vacuum to the distributor vac advance and the trans modulator. I run the fat vacuum (manifold vac) nipple to the pcv. I run the power brake booster off an NPT hose fitting on an intake runner (also manifold vac). Your intake manifold may not have a vacuum nipple. I cap off the ported vac source since I like manifold vac for the distributor.

[STEELCITYFIREBIRD]

What cam, cubic inch, head # or cc and/or compression ratio if you calculated?
Timing at idle?

[Carmine]

I certainly have some work ahead of me. I wish I had more answers to the questions posted. The engine is numbers matching 400 cubes. Don't know if it was rebuilt/bored or what the pistons are for a CR. The heads are stock appearing #96. Don't know if they have been reworked. The camshaft, all I know is that it is far from stock. Don't have a clue as to the numbers. The timing I can check on. Will do that today. What should it be set at initially?? With an HEI distributor, would you turn it while monitoring the engine vacuum for the highest inches, then back it off 2 degrees?? I'm told that is one way of doing it. I have a suspicion that this car has seen a fair amount of drag racing. With the former Edelbrock Performer RPM intake, Holley 850 carb., after market headers, all of which I removed and replaced, plus the HEI and aftermarket posi with 3.55 gears, I do wonder. I'd like to mention again, that I tested all the ports available for vacuum, and got a consistent 10 inches. I'll attempt every thing that is suggested, but I'm just not optimistic that I can do better. Thank you all, Carmine.

[74Grandville]

may be a big cam with low compression. what psi do you get with a compression check? won't tell you everything, but may give some kind of indication.

[Carmine]

Originally Posted by 74Grandville

may be a big cam with low compression. what psi do you get with a compression check? won't tell you everything, but may give some kind of indication.

I don't know. Never did a compression test, Carmine.

[Carmine]

Originally Posted by STEELCITYFIREBIRD

What cam, cubic inch, head # or cc and/or compression ratio if you calculated?
Timing at idle?

Warmed the engine to 180 degrees and checked the timing. First pulled off the vacuum advance line on the distributor and held my finger over the hose. I could feel a little sensation of a vacuum pull. Even when the line was off, it didn't change the idle of the engine which was at about 850 rpm's. Hmmmm..................Not sure what that means. I checked the timing which was a solid 8 degrees BTD. The marking/line varied little to not at all. I haven't looked up what the factory recommended timing advance should be, but seeing how this is a non factory cam, not sure how important that would be. I know very little about timing, but I don't think this is enough. I'm thinking 12 degrees should be a starting point. My almost stock '62 409 has the timing advanced to initially 12 degrees, and runs great and cool. Any thoughts/suggestions?? Thank you, Carmine.

[STEELCITYFIREBIRD]

Likely just over 8:1 compression with #92-96cc (heads) unless those are round port exhaust ram air II heads ( unlikely but verify).

As stated a cranking compression test psi could indicate if the cam is just way too big for the static CR. I believe < 150 psi would be the breaking point, others may provide better limit.


First I would find a solid source of vacuum at idle and connect the vacuum advance there, then adjust idle speed to reasonable/previous # and check vacuum now, also with car in gear. If you get a nice bump in vacuum your on a good path.

Then Advancing the timing or just using manifold vacuum should increase idle vacuum, then readjust idle mixture.
A set of Rhoads lifters can give you a nice bump in idle vacuum too.

Are you looking to increase vacuum, how to correctly hook up hoses, other??

[geeteeohguy]

What year and what engine?