Do I need this 5 port vacuum switch? If not, what do I mostly likely do without it?
I had my 69 350 rebuilt. It now has an Edl RPM Intake Manifold, and EDL 650 CFM 4 bbl Carb, also the car will have after market AC, No PW yet anyway, PS, PB, Auto Conv top. Not sure what else even matters.
My vacuum switch is damaged. It has one of the five ports broken off and the bottom or sixth nub is broken off.
What should I do? Track one down or work around it.
The 5-port switch was used on the 1969 auto trans Pontiacs. Its intent was to divert (or bypass) vacuum to the vacuum advance when the engine temp rose to 230 degrees. The bypass would allow another 20 degrees of ignition timing to cool the engine down.
The same function was handled by the 1968 dual-port vacuum advance cans.
It's not a necessary part, but of course it's a desirable part from a restorer's point of view, because it's right up in front of the intake manifold in a highly visible location. Currently, 3-port units are available, but the 5-ports are not (unless it's changed in recent months). I sold two of these 5-port units, both of them were aftermarket parts I picked up in the 1990's, for $125 each on E-Bay. Factory GM units fetch $150-$200 or more.
If you run full vacuum advance, there's no need for the TVS (thermostatic vacuum switch).
BTW, in later years, the TVS unit not only controlled vacuum advance, but also when to engage the EGR solenoid.
Most of the guys now only use them for show. You can find them for about $50 now if you watch this site, Ebay or the PY site. They are not pulling the big money they used to. Someone is also now repopping them and selling them new for $75, I think NPD is carrying them...
Also, they were used on 68 and up and on auto or manual, did not matter, the vacuum line routing and connectivity was different between the two. Late in 68 they revised and only used 3 of the 5 ports thus in 69 a 3 port TVS came out. Over the following years various configurations of the TVS came and went...
I may have been incorrect on the usage (years) of the TVS, but the info came from Pontiac Enthusiast Magazine, and I just found it here on FGF.
The TVS-GM#3016754 is used on all 1968 V8's and on 1969 V8's with automatic transmissions. Also, several early production 1969 Ram Air III cars with manual transmissions were built using the TVS and the vacuum advance valve. The 1971 455 HO engine also used the TVS with either transmission.
In all applications, the TVS serves as a safety device to help prevent overheating. The switch is located at the front of the intake manifold, threaded into the coolant passage. There positions inside the TVS related to coolant temperature. Standard vacuum flow is ported vacuum from the carburetor to the distributor vacuum advance. Whenever the engine coolant temperature rises above 230 degrees F, the TVS switches the distributor advance from ported to full manifold vacuum. This advances the timing about 20 degrees at idle, allowing the engine to cool down to normal operating temperature. After the engine cools, the system returns to ported vacuum.
Either way, it's not necessary, but the restorers were paying a hefty premium for the 5-port job a few years ago when a friend told me to sell the two I had! I thought they were worth about $10, but he was right, they both sold for $125+.
Yeah a few years back they were bring a decent penny, not any more. There is a guy on the PY site selling them for $50 and he has several of them in very nice condition...
