Ok - I'm thinking of adding a PCV (Positive Crankcase Ventilation) system along these lines to replace the draft tube on my truck and I have a naive question for you: where do I tap in to the intake manifold for vacuum for the PCV valve if my dual action fuel-pump (and in turn, wiper motor) is already using the only fitting on the manifold? See the picture below to see my current (factory) setup. Do I replace the current manifold fitting sucking on the fuel pump with a "tee" so I have two lines running into the current vacuum source in the manifold (the second pulling on the PCV valve)? --- or --- Do I pop out the plug just above my fuel pump vacuum source and run a new fitting into it for the PCV valve? --- or --- ? Sorry for such a silly question - all the examples of retrofitted PCV systems I have found on-line appear to be running only the PCV valve off of the vacuum fitting currently used by my fuel pump / wipers...and I can't see where those fuel pumps are getting re-plumbed (if anywhere) post PVC install. Particulars: my engine is a 248 GMC - completely stock. Thanks for your advice everyone! Roland.
Nice engine compartment! You could get a four way "T" or "cross" and one up close nipple which would give you three outlets or just coat a drill with axle grease and drill a second fitting hole. Coat the tap with grease also. I have never had a problem doing this but if in doubt the carb could be pulled and a magnet run down to pick up any tailings. IIRC the factory hole has a 1/4 NPT thread.
Me thinks you got gypped Roland. Below is a picture of my '52 GMC 228 showing three vacuum ports. All three now have brass fittings installed. The top one under the carb is 1/2" NPT thread. I've hooked my PCV system in there. Just below it is a 3/8" NPT fitting providing vacuum for my brake booster. On the top of the manifold runner, near the rear, is a 1/8" NPT brass plug in the hole that the wipers (now electric) were attached to. Your manifold is obviously different, starting with the orientation of the carb mounting studs.
Evan & Bill - thanks for the insights! Bill - I don't think I got gypped - below is a close up of mine - it has a 3/4" unused port (plugged) above the fitting to my fuel pump/wipers... I guess I can use that for the PVC setup much like Bill has done... agreed? Otherwise, if I have been ripped off, I guess I can just part out the truck <jk> ;-)
Roland ; You need a larger diameter fitting to properly operate the PCV valve . There was one that screwed into the 3/4" NPT port in the center of the intake manifold that also had a small nipple for the wiper feed . I know many 1970's Brand 'F' (yes , I know,deal with it) products had *just* what you need here . FWIW , adding a vacuum tank up under the dashboard will prevent the wipers from stalling out when you stomp the foot feed on that romping stomping GMC L O N G motor ! = .
