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Old 03-01-2008, 02:05 PM
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Vacuum Line Routes

I have a 1987 Monte Carlo SS with a 1976 Monte Carlo 350 (383) and a TH350 with a vacuum modulator. So i have to route all of the vacuum lines. Here's what i have:

Brake Booster
Tranny Modulator
Vacuum Advance Distributor
PCV Valve


The carb has a vacuum fitting out the back and the intake (Edelbrock Performer) has a fitting as well, but no EGR.

So i was planning to put the tranny and distributor off the carb and put the PCV valve and brake boost to the intake. But then i wasnt sure if the PCV has to go to the carb for mixture reasons. Do i have the right setup?

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Old 03-01-2008, 02:26 PM
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Tranny line should be by itself from everything I have seen and been told. It is alsoa long run, use steel and no more than 4 IN of rubber on either end.
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Old 03-01-2008, 02:30 PM
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So which one should i run the tranny from carb or intake?
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Old 03-01-2008, 02:30 PM
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PCV typically gets the big 3/8" barb at the front of the carb. Brake typically gets the 3/8" barb at the back or on the manifold. Ignition on that car gets ported vacuum, so you have to make sure the carb source you're giving it is actually ported vacuum. not all carb ports are ported, some are manifold.

There is a sticker on your radiator support that has all the vacuum line routing on it. If you don't have that sticker, go visit any other GM car from about 75 to 92 and it will be basically the same.

Tranny gets manifold vacuum.

In a nutshell on your car: These things get ported vacuum
- ignition
- small signal hose to the charcoal canister
- EGR

These get manifold vacuum.
- tranny
- PCV
- brakes
- big purge line to the charcoal canister

After that, it doesn't really matter where you source the signal. As long as the brake, PCV, and charcoal canister get the bigger ports, hook them up where ever is easiest and gives the proper signal.
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Old 03-01-2008, 02:39 PM
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So if the tranny need manifold vacuum as well as the PCV and brakes, how would i route them since the tranny is supposed to be by itself?
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Old 03-01-2008, 04:44 PM
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Biggest question is what carb do you have? If you have a Holley, it's going to be tough. If you have a Qjet, it's much easier.

For a Qjet:
Rear of CARB base plate hole takes a fitting for the booster.
Front of CARB base plate 3/8" pipe goes to PCV.
The hole in the back of the performer intake will accomadate a fitting with multiple 1/8" barb fittings. These can be used for the trans modulator, A/C and heater controls.

One thing to keep in mind, it is NOT recommended to "T" the brake booster and PCV together. Some say it's ok, but it's really NOT a good idea!
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Old 03-01-2008, 05:28 PM
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The vacuum source above the #8 intake manifold runner can be used for anything that needs a full manifold vacuum signal, but does not leak air.
Auto transmission vacuum modulator and power brake booster can go there as long as they don't leak air. If what ever you hook up there, leaks air or does a purge function, the #8 cylinder will run lean. You don't want that. Check your power brake booster, hoses and inline check valve for a air leak fault, first.
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Old 03-01-2008, 05:43 PM
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I have a Holley 650 vacuum secondaries. I was just looking a it, there is a small, like 1/8 inch port that stick out by where the fuel hooks up, then on the other side there is a 3/8 port. So the 1/8 inch would be ported vacuum and the 3/8 would be full manifold vacuum correct.

Then i would have two full manifold vacuum holes for PCV, brake, and tranny and the 1/4 would be the distributor advance.

What if i did this:

Ran all three things (PCV, trans, and brake) off of both full vacuum holes by connecting the carb and #8 manifold ports then splicing the three into that.. Then if there is a leak it would affect the entire engine just a little bit not just #8 cylinder. Or would that give me way to much vacuum? Just an idea. It seems like my theory is right, but might not actually work.

How would you go about checking the brake booster for air leaks?
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Old 03-01-2008, 05:49 PM
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I got another idea after rereading this.

Quote:
Originally Posted by F-BIRD'88
The vacuum source above the #8 intake manifold runner can be used for anything that needs a full manifold vacuum signal, but does not leak air.
Auto transmission vacuum modulator and power brake booster can go there as long as they don't leak air. If what ever you hook up there, leaks air or does a purge function, the #8 cylinder will run lean. You don't want that. Check your power brake booster, hoses and inline check valve for a air leak fault, first.
Why wouldnt i just run the PCV and brakes into the carb fitting and then run the trans into the intake fitting. Then there would be less chance of leakage. And it seems like the PCV should go to the carb anyway or the #8 cylinder would run rich.
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Old 03-01-2008, 06:02 PM
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if your power brake booster leaks air it is faulty and your power brakes will be marginal. If you hook up a faulty PB booster to the #8 runner spot, #8 will run lean. (you can damage the engine) If you pair the PB booster and PCV together on the 3/8" port on the back of the holley you may/will have problems with the PB's. If you pair the PB and PCV together on the 3/8" port on the back of a holley and the PB booster does not leak you probabily won;t have a problem ( I don;t even with a radical camshaft).
If you're PB booster is marginal, (test drive your car and see.) don't hook it up like that.
The amount of available manifold vacuum is the same.
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