I have a 1406 Edelbrock carb that I am plumbing vacuum lines for. I have the booster hooked up to the rear manifold vacuum. I am trying to decide if the ported vacuum can be used for the tranny modulator or the HEI vacuum advance. I have read on Edelbrocks site that the ported vacuum is used for emissions controlled cars… That's helpful. I think the GM HEI is set up for ported vacuum , but I can't prove it. I had thought about adding a T in the manifold vacuum in the rear for the modulator valve. The internet is littered with theories and arguments. Someone tell me the gospel.
Root, if you search C9+vacuum you will find about 5 pages of threads where he discussed this. Here is but one. http://www.jalopyjournal.com/forum/threads/ported-or-manifold-vacuum.314524/
most vac advances on the dist. are designed for ported vacuum. i know you can run them on full vacuum but i have never had good luck using it. the trans should be on full vac.
Manifold vacuum. Are you building a tree hugger car or a hotrod? I'm all for saving the planet but my hotrods will not cause enough harm to worry about. Personally I'd ditch the HEI (they are ugly!!!!) and use a dist from the sixrtys. You can convert them to electronic and they are good to go. If you can't... get Bubba to do one for you. He can set it up for how you plan to use your car and not a soccer mom. All the GM dists used manifold vacuum. This was never a problem until they started to make universal-fits-all Carbs and everyone got confused. If you are worried about the air buy a Prius.
That's what I thought. Why would a hotrodder want modern emissions gear? None of the pre emissions cars had ported vacuum on their carbs. It's a modern thing. You can't tell by where the vacuum connects to the outside of the carb. The port inside goes down under the throttle plates to get manifold vacuum even though it connects to the carb high above the butterflies. Confuses a lot of people. I don't know a thing about emissions gear and I really am not interested.
I'm not either. Read the original post. I am trying to make sure I get the right port. Never mind. I'll continue to research it.
My Edelbrock 600cfm on my present engine likes manifold vacuum. I tried both and suggest you do the same. At the end of all my searching and research, I found that every person, engine and preference were different. Tree hugger? It's amazing some folks thinking is limited to the late 1800's.
Manifold for vacuum advance. Good reading here, http://www.lbfun.com/warehouse/tech_info/timing & vacuum advance/Vaacuum_Advance_Specs.pdf
"None of the pre emissions cars had ported vacuum on their carbs." ====================== US emissions history - starting with newer. "The Clean Air Act of 1963 was the first federal legislation regarding air pollution control. It established a federal program within the U.S. Public Health Service and authorized research into techniques for monitoring and controlling air pollution." In 1963 California mandated PCV valves on all new cars sold in California. Around 1961 California mandated PCV valves (HARDWARE) on sanitation department trucks. "The Air Pollution Control Act of 1955 was the first federal legislation involving air pollution. This Act provided funds for federal research in air pollution." http://www.innova.com/en-US/Support/ObdKnowledge ===================== Attached are two images. One is from the 1951 Chevy Service manual describing how they ran their vacuum advance back then. Another is from a much older Audels "New Automobile guide". The Cover is my avatar. Note it is olde enough that the carbs in schematic Figs 6 and 7 are updraft so the "carb side" and "engine side" of the butterfly is opposite to what we see on most cars and practically any V8 I can think of . regards, Dan T
Not entirely true, but for performance purposes, yes. You did run into 'ported vacuum' setups (Ford in particular loved 'em in the 50s), but they rarely worked all that well...
Hi Steve, the quote "None of the pre emissions cars had ported vacuum on their carbs."was by someone else. I was responding to it. There is tons of evidence that plenty (not all, but maybe even a majority) of manufacturers use ported vacuum to control the vac advance decades before emissions were in any manufacturer's engineering department's vocabulary. regards, Dan T