Buick Rodders, I am trying to figure out the vacuum line routing for the 430 with a 400 trans. The temperature sensing unit with three connections is listed and pictured with the line connections in my shop manual but there is little written description on what kind of vacuum, either ported or straingt manifold. Also, what temperature is the valve going to open at? Any info along these lines (no puns intended) would be greatly appreciated.:beers2: Doug
Doug, Since you are posting in the Race Forum, I have to ask, why are you concerned with the thermo vacuum switch? Most racers would chuck that first thing. It's unnecessary. The 1970 switch has 3 nipples, and they are marked, MT, C, and D. MT is Manifold vacuum, C is ported vacuum from the carburetor, and D goes to the vacuum advance unit. During normal operation, the vacuum advance gets ported vacuum. If the coolant temps get above 220*, the switch applies manifold vacuum to the vacuum advance. That cools the engine down under normal conditions. Most guys just eliminate the switch and run a vacuum line from the carburetor to the distributor. I use manifold vacuum all the time. The engine will run cooler at idle and low speed, and the vacuum advance will respond quicker to changes in engine load. Hope that helps.
