# 68 GTO Vacuum Switch



## Norms68 (Jul 17, 2013)

So I pulled my engine this weekend and noticed the 5 port vacuum switch hoses are very loose and most likely leaks. Also 2 of the ports are jumped together. One port goes to front of carb, one port goes to side of carb, and last port goes to the dist.

Do I even need to run through the thermal vacuum switch?
-Norm


----------



## Matthew (Feb 11, 2011)

Norm, I thought about bypassing the TVS too. It is not intuitive as to what that little fellow could be doing in the overall scheme of things. Most of the folks I have talked to about it say it can be eliminated if you have the manifold and ported vacuum connections to support your set up. My only requirements were a two port vacuum advance and hide away headlights. You may have other requirements like power brakes and AC. I even tested the bypass with no noticeable difference.

Now, I was good with the bypass idea until I came across the explanation below on the TVS purpose. I have no idea if it really works this way, but seems to make some sense. Some things I just accept - this is one of them. The car came with a TVS, it operates very well in that configuration and I'm not looking to out think the engineers on this one. Decide for yourself. Regards, Matt 

_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 are 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._


----------



## Norms68 (Jul 17, 2013)

Thanks good to know,

I have my hide away lights and brake boost off the rear manifold vacuum. Single port advance. I've seen about 50/50 on bypassing or not. I have 2 engines, I think I'll run thermal vacuum switch on my original 400 and bypass for my 461 stroker.

Thanks,
-Norm


----------

