I have an 87 Firebird originally equipped with a tbi 305. It has a 350 GM crate motor with an Edelbrock Carb and manifold now. When I got the car a little while back there were vacuum lines rotted out, missing or probably on the wrong ports. There's a couple ports on the carb and one on the manifold behind it. I know there's manifold vacuum and ported vacuum. My question is: which port, manifold or ported, does the vacuum advance, cruise control and heater A/C hoses go to? All on the same or some ported and the other manifold. I think they are the only 3 vacuum things being used now. Thanks

 

Cruise & HVAC go to straight manifold vacuum. (not ported) HVAC additionally requires a check valve and an accumulator (vac storage), arranged such that when there's more vacuum in the manifold than in the accumulator, the check valve allows more vacuum to fill (empty?) the accumulator; and the car's subsystems are in effect supplied by the accumulator, which is kept constantly topped off by the engine vacuum, and prevented by the check valve from vac going the other way (draining from the accum back toward the manifold).

Vac adv can go to either. Hook it to each and see how it behaves. Ported vac to the dist was introduced by the factory as an emissions control, not to make the engine run better or otherwise have any positive properties to the user; but in spite of that, it can be preferable. Often it depends on your particular distributor and its vac adv diaphragm properties. But a "hot street" car will generally run better with non-ported vac to the dist, as long as the idle is stable. Try both and see what works best for YOU.

 

In the 1980s, Chevrolet (and most Manufacturers that were still using engines that were designed decades ago) were scrambling to try and meet the ever-growing Federal/ State Emissions standards.

In the situation of the the Gen-1 SBC...
Chevrolet wanted these Engines to run hot and as lean as they could get away with.
By using a "Ported" Vacuum source for the Distributor's Vacuum-Advance...
Expressway driving could yield slightly better Fuel Economy, and slightly better aspects of unwanted Emissions.

There was no magic solution for meeting Emissions standards...
as the levels of the different compounds (that are emitted via Engine Exhaust) are varied by different means.

Making the Engine run Hotter and Leaner helped reduce various HydroCarbon Compounds (such as Methane Gas) and MonoCarbon Monoxide.
However this will increase the levels of the various Nitrogen Oxide Compounds (some worse than others) produced.
As such other Emissions Control Devices had to be implemented...
Secondary Air Injection, Exhaust Gas Recirculation, Catalytic Converters, and allowing the Engine to operate at a more optimal Temperature, and Air to Fuel Ratio.

 

I had GM cars from 1979 through the early 90s. The vacuum lines and gadgets were very frustrating to work with. I was so happy when the electronic fuel injection and the electronic controlled systems started being used. It seemed like better fuel economy and less repairs. Thanks for the remarks. I have, since first posting, put a T in the vacuum line from the intake to the heater and cruise control line and to the vacuum tank. I capped the ported vacuum and the distributer is running on the continuous vacuum from the carburetor nipple. I'll try this out and see how it does. Then I will try ported to the vacuum advance and see it's results. I'll let you know what my experience with it is.