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I'm mounting an Offy manifold with 3 Rochesters on my '55 Chevy 265 small block. The manifold itself has no vacuum port, but all 3 carbs have vacuum ports on their bases. Only the center carb has an idle circuit, and the end carbs are modified so the butterflies close completely. Where is the best place to pull off the vacuum for the brake booster? Or does it matter?
hey. as far as i know the best place to pull vaccume is the center carb in the back low in the base, there should be a plug there to do it. if there's no plug then you are going to have to deciede if you want to drill and tap the manifold for vaccume or to get a vaccume pump to solve this problem,so let us know how you make out or if you came up with anything else.
take it off any of the 3 carb bases, as long as the source is below the throttle blades, whether they are completely closed or not. They'll all be closed when you're on the brakes, unless you're a maniac :whacked:
I've run the same setup on several SBs. Personally, I'd use a tight 90 degree fitting on the center carb with a 3/8" hose fiting for a PVC valve, and another 90 off the rear carb for the brake booster.
If your going to be retaining the original road draft tube you could use the the center carb for the booster.
Thanks a lot for the advice, guys. I have installed a right angle fitting at the base of the center carb, which should work okay. I'll let you know how it works when I get it on the road.