My heat riser flap is rotted out of the exhaust, going to delete the EGR and use an aftermarket air cleaner. Looking for a diagram of the basic vac lines needed. The manifold 4 port vac unit on top front is also broken in half. can I block it and use just ports on carb, vac unit on the front of the block, and one on manifold behind the carb?
I see guys asking for vacuum diagrams all the time. Completely unnecessary. The thermo-vacuum switches on the intake were part of the emissions controls. Get rid of them. There are two types of vacuum, ported vacuum, and manifold vacuum. It helps to know the difference between the two. Ported vacuum comes from a source ABOVE the throttle blades. At closed throttle, there is no vacuum at a ported nipple. As you open the throttle, vacuum increases rapidly. Manifold vacuum comes from a source BELOW the throttle blades. Manifold vacuum is there at closed and part throttle. Both Ported and Manifold vacuum will be close to if not ZERO at wide open throttle. At part throttle, ported and manifold nipples will read the same It is very easy to tell the difference between ported and manifold vacuum on an engine running at idle. If you pull the hose or cap off a ported vacuum nipple, you will hear nothing. If you pull the hose or cap off a manifold vacuum nipple, IT WILL HISS LOUDLY because you have just created a vacuum leak. Now, what takes what? DISTRIBUTOR VACUUM ADVANCE- You can use ported or manifold for this. I say try both, and see what you like. At part throttle, they will be the same. Manifold vacuum will give you extra advance at idle which can help with coolant temperatures at idle and stop and go. TRANSMISSION VACUUM MODULATOR- Manifold vacuum only. AIR CLEANER SNORKEL DOOR- Manifold vacuum only. CLIMATE CONTROL STORAGE CONTAINER- Manifold vacuum only EXHAUST GAS RECIRCULATION, eliminate it. ALL CHOKE PULL OFFS- manifold vacuum only.
Thank you. I do get the ported and manifold difference. What still confuses me is why a ported spot on carb is on a tee to the tvs and efe switch? I don't get why you would connect three sources of vacuum together.
The switch selects different vacuum according to need. A perfect example is the Transmission Controlled Spark System used on the 70 and up 350 and 455. Ported vacuum was used for vacuum advance, and the relatively retarded initial timing caused the engine to run hot under certain conditions. When the temperature got over 220*, the switch would supply manifold vacuum to the vacuum advance canister, providing more timing to cool the engine down.
