[i4abuygto]

I acquired a 79 Trans Am - 403 and need help with the vacuum system under the hood.
The car has an aftermarket intake - edlebrock performer with Holley 750 and headers.

With the intake conversion the previous owner butchered the under the hood vacuum system. Non of the aircleaner vacuum lines are currently used.

The engine runs strong - no emmissions - internals are unknown. I need to figure out the vacuum system that will work. Perhaps someone can help me with what is necessary and what is not.

I have found that currently, the vacuum advance on the distributor is not hooked up. Nor is the charcoal cannister, any of the vacuum lines associated with the air cleaner (except the main line down to the valve cover), or the small vacuum line that controls the AC system that is supposed to have a check valve off the intake.

After market chrome valve covers are also added.

I have attached two photos of diagrams of the basic 403 vacuum system. The first photo is a diagram that I found for reference - the second photo is edited to show what is not hooked up on my system (circled in red) - the yellow shows the manifold vacuum going down to the transmission and that is all that is currently hooked up to the manifold vacuum.

My brake booster is to the rear base of the carb and noted in Blue on the second photo.

I have a vacuum port open on the front base of the carb that I believe to be ported. I think I need to plug that line and run the distributor, transmission and AC controller off of the Manifold Vacuum - is that correct?

Can I connect the check valve for the AC controller vacuum by splitting the manifold vacuum to run to the distributor, transmission and AC Controller?

What is necessary on all the other components not hooked up and what is the simplest way to include them if they are necessary to get the correct performance? Can I bypass or remove the cannister?

Please advise.

Thank you.

[Schurkey]

Trans modulator and distributor vacuum advance shared a manifold vacuum source. They can share a manifold vacuum source again. Tune the distributor centrifugal and vacuum advance for best performance.

PCV valve is probably going to have to go to the 3/8 nipple on the rear of the carb. I think your brake booster is connected there now. The brake booster will go to a nipple on an intake-manifold runner instead. (Optional--leave the brake booster connected to the rear of the carb, drill the cast-in boss on the baseplate on the front of the carb for a 3/8 nipple Holley should have provided, that the PCV can use. Be sure the PCV fumes are routed to both intake manifold planes. Not all carb bases have the appropriate boss that can be drilled, and distribution channels for the fumes. Maybe you'll be lucky.)

Reconnect the charcoal canister using manifold vacuum, ported vacuum, and the plumbing from the fuel tank as shown in your diagram. There probably is no carb bowl vent nipple on the Holley, so cap that port on the canister. Make sure the plumbing back to the tank is unblocked and actually connected.

I'd have expected a vacuum hose to a thermostatic vacuum switch, and from the thermo-switch, to an air door motor on the air cleaner housing, to run the flapper that meters hot air into the air cleaner. But the only thermo-switch I see appears to go to the rear choke pulloff of the original carb, which the Holley won't have. Apparently, that air cleaner doesn't have the heated-air intake. Strange. At least that saves you from having to fabricate a stove around one of the header tubes to provide the heated air.

A/C system will draw vacuum from manifold, not ported vacuum. Yeah, I'd expect a check-valve.

No EGR valve, no need for EGR vacuum plumbing.

[i4abuygto]

Thank you Schurkey,

Your write up on the vacuum system will be very helpful and fairly easy to follow.

I have not tuned a distributor before so I will look into that.

If the easiest way to have the PCV routed to both planes on the intake is to attach to the rear base of the carb, I will likely do that and find another source for the brake booster.

I will route the AC vacuum line to its own dedicated source on the manifold and the trans and distributor together on another.

After these modifications the shaker scoop air cleaner snorkel set up will have no valves inside or any vacuum lines connected to it. The filter element will effectively be an open element under the shaker scoop, inside the snorkel filter housing- is that correct?

Is there anything else I need to consider?

Thank you

[i4abuygto]

PCV valve is probably going to have to go to the 3/8 nipple on the rear of the carb.

With my current configuration (and the diagram for the 79 403) does the stock PCV valve run from the left side valve cover to the air cleaner snorkel housing - If so, can I use that configuration or is that not recommended?

[Trevor78]

Do you have the relevant service manual, all information and diagrams are shown.

[Schurkey]

Originally Posted by i4abuygto

With my current configuration (and the diagram for the 79 403) does the stock PCV valve run from the left side valve cover to the air cleaner snorkel housing - If so, can I use that configuration or is that not recommended?

Originally Posted by Trevor78

Do you have the relevant service manual, all information and diagrams are shown.

Good advice.

I would have expected--and your illustrations show--that the PCV valve is in the right valve cover, the left cover would have the fresh-air inlet. "Left" and "Right" are taken from a person sitting in the driver's seat, not standing in front of the front bumper.

[Trevor78]

0.5 secs on google.

https://cdn3.volusion.com/klmat.yytx...che=1477632079

[Cliff R]

You've got to love the "cobbling" involved with installing aftermarket parts. Even worse none of the parts mentioned or being used here except maybe the headers make any more power than the factory parts removed. About all that happens after jumping thru all the hoops to get the carb and intake installed and vehicle running is that you took 27 pounds off the front of the car.......FWIW.

Holley should have included two 3/8" manifold vacuum ports on their street carburetors. This certainly would have made it a LOT easier to hook up power brakes and PCV. Those charcoal canisters should never be hooked back up to the carb anyhow. Not sure how but even though they are downhill and several feet from the carb a LOT of charcoal can migrate into the carb nearly filling the float bowl in some scenarios. We always removed or plugged the large hose from the carb to the canister on all those vehicles way back when there were still relativley new........

[i4abuygto]

Do you have the relevant service manual, all information and diagrams are shown.

I have manuals for the 79 and the diagram I attached earlier was for the 79 403 (code K) engine.

Thank you for the photo link-
The previous owner did not have a PCV valve in the system which is why I was mistaken in looking at the diagram and I confused the PCV air in (left valve cover) with the missing PCV valve (to the right valve cover). The PCV air in to the left valve cover was plumbed in from the snorkel at the time of purchase.

Answers to all the questions is why this forum and you guys are much appreciated.
I will be purchasing a PCV valve and running it to the base of the carb.

Is the PCV air intake from the left valve cover necessary or is it optional?

You've got to love the "cobbling" involved with installing aftermarket parts. Even worse none of the parts mentioned or being used here except maybe the headers make any more power than the factory parts removed. About all that happens after jumping thru all the hoops to get the carb and intake installed and vehicle running is that you took 27 pounds off the front of the car.......FWIW.

I acquired the car with all the aftermarket intake parts - not my choice to do it this way. I believe it is probably easier to make what is here work correctly, than to source out original parts.

I think the previous owner had good intentions - the engine is far from stock and runs strong - head work, upgraded rear end, headers and different cam for sure. He had lost the paperwork on the engine and head work so internals are unknown. Rear end I believe is approx. 3.25 gears. Because of the added performance, he installed frame extensions. This was apparently an ongoing 10 year, drive as you go, project for him.

Dash was all carpeted - heater core was bad, none of the AC plumbing or electric was hooked up and behind the dash was a mess with hacked wiring and a lot of missing ducting and bracing. I am working on fixing it all and getting it right.

I got a real good buy on the car and it is rust free and for a Minnesota 79 car that is unheard of.
I was just going to buy it, install a different engine with pop, and flip it for some quick cash. I wasn't going to keep it or do any additional repairs - just flip it. When I test drove it, I found out the engine ran way stronger than I expected it would. Definatly not a stock 79. When I brought it home my wife drove it and fell in love with it- wants to keep it but I have to get the AC working - which landed me here. More whoop ass.

I have an extra Muncie 4 speed with a 69 400 that was built for my 67 GTO before I opted to rebuild the original WS engine. Some day, down the road, I might put the 69 400, 4 speed in the 79 TA where all this vacuum info will be very helpful. And it will be crazy fast for a 79.

Any more additional Street advise would be welcome.

Thank you

[Schurkey]

Originally Posted by i4abuygto

Is the PCV air intake from the left valve cover necessary or is it optional?

Some form of clean-air inlet on the opposite side of the engine from the PCV valve is essential. Using the OEM parts in the original location is wise.