Whons Posted January 16 Share Posted January 16 I always run the vacuum hose to my advance on the distributor to full manifold vacuum. Time the engine to specs with the hose removed and plugged, then to make sure that it is working rev the throttle and make sure the mark on the harmonic balancer moves farther in the advanced direction. I have always done it this way on all my SBC's that I have owned. I have even had arguments over this. A lot of guys think it should be run to ported vacuum. That was only done on newer cars once they started putting emission controls on. Let me know what anyone thinks about this subject. Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 16 Share Posted January 16 Always to ported vacuum. Manifold vacuum has the vacuum advance advanced at all times and usually way too far advanced. Where you usually have to have initial timing lower than optimum. HEI distributors for some reason over advance badly. And usually the centrifugal advance is very slow if you have not changed the advance springs. I believe your way is leaving performance, milage and efficiency on the table to be gained. My opinion... 1 Quote Link to comment Share on other sites More sharing options...
John S Posted January 16 Share Posted January 16 44 minutes ago, MC1of80 said: Always to ported vacuum. Manifold vacuum has the vacuum advance advanced at all times and usually way too far advanced. Where you usually have to have initial timing lower than optimum. HEI distributors for some reason over advance badly. And usually the centrifugal advance is very slow if you have not changed the advance springs. I believe your way is leaving performance, milage and efficiency on the table to be gained. My opinion... Let me ask you a question if I can Thomas regarding my vehicle. With the four speed, the car is supposed to have the TCS switch which controls vacuum to the distributor. The transmission is an older M20 without the TCS switch on it. I am missing the TCS solenoid, but all the wiring is there on the car. There are no ported vacuum outlets on the carburetor, what would you suggest then? The vacuum port on the carburetor that should go to the TCS solenoid now goes straight to the distributor and is full vacuum. Going back to a post I recently posted in engine tech maybe the advance is why the car won’t idle down. I would appreciate your thoughts on this. John S Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 16 Share Posted January 16 There is always ported vacuum and constant (manifold) vacuum on carburetors. I believe the tcc does not let the distributor fully advance until the car is fully warmed up. It's been a long time. Lolol 2 Quote Link to comment Share on other sites More sharing options...
jft69z Posted January 16 Share Posted January 16 It also allows advance in the high gear only, or the lower gears if the engine is in a high temp condition to help it cool down. Here is info regarding the 1970 TCS system: Here is some info regarding vacuum advance (check the 'Ported Vacuum' heading too): http://www.camaros.org/pdf/timing101.pdf http://www.camaros.org/pdf/map_advance.pdf 1970 TCS system.pdf 2 1 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 16 Share Posted January 16 Thank you Joe. I didn't remember fully. 1 Quote Link to comment Share on other sites More sharing options...
stangeba Posted January 16 Share Posted January 16 WOW, TCS! I remember it well because I removed it all from my 71 350 4bbl, in May of 1971. I have run ported since then. My brother in-law worked at Chevrolet in Warren Michigan at the Tech Center, in the engine department and he is the one who suggested I set it up this way. I had lots of fun hanging with him and his friends. 3 Quote Link to comment Share on other sites More sharing options...
420ponies Posted January 16 Share Posted January 16 With my Holley carb, turbo 350/ Th2004r , it used ported with the HEI. Better response throughout the rpm band. That's a 750 vacuum secondary on a 355cu.in. SBC. Same carb going onto the BBC for the debugging phase for the new drivetrain. Can't wait !! Going with a D.U.I. HEI unit. Might have the built in rev limiter, just because...... 2 Quote Link to comment Share on other sites More sharing options...
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