I apologize for re-asking an old question. Still, I’d like to understand it better, and re-reading old posts isn’t always the best way to do that. I hope you’ll keep in conversation with me.
bubba22349":bayymfvp said:
This subject comes up from time to time and there are a couple different views. First on the ported vacuum only being a '70s emissions gimmick,
that sure is a load of BS. Ported vac. was used long before the Smog emissions era.
I checked Google Patent, and found patent number 3400698, dated December 22, 1966. It appears to be for ported vacuum. I also checked its references to prior art, and found a 1957 patent (2809620) for a vacuum advance/retard mechanism designed to get the car to warm up faster.
According to the 1966 patent, the faster warm up is desireable to reduce NOx; a major component of smog. Efforts to reduce smog in the LA Basin date back to at least the early 1950s, IIRC.
So what’s the non-emissions advantage to ported vacuum? Just the faster warm up on a driver? That’s what I’m trying to understand.
Next to make the right choice what is the planed use of your car? If it's a race apt. than you don't even really need a vac. advance! A vac. advance was designed to give the best driveableity and economy for a streetcar.
This is definitely a street car. No racing intended. I’ll do it the factory way if that’s the best way, I just want to understand why the factory did it and if anything in the intervening 43 years has shown they should have done it differently.
It takes some different tuning methods and skills to make the right mods for the system to work correctly. The only way to know if you like one way or an other is to try them all.
I’m definitely not happy with the way its running right now. I’m not sure that can entirely be blamed on the ported vacuum or not, but it seems the thermostatically controlled switch for going between ported and manifold vacuum was never installed when the late engine was put in my early bird, so maybe that’s part of it.
Lastly will throw in my .02 that if it’s for a street car that's a D.D. and you expected to get reasonable street performance, have an interest in the best MPG I would want use a ported vac. source if it was there.
Does running hotter yield better fuel economy? Obviously a cold engine won’t vaporize fuel very well, but as I recall most of the ‘50s and ‘60s engines that survived into the 1970s and 1980s suffered a serious fuel economy hit because of the first-generation emissions gear they had to wear. I thought some of this was due to the increased operating temperature.
I’d love to know more about ported vacuum. If there are some threads that explain why to use it, I’m interested to read them. All I’ve seen so far really seem to advocate its use because it’s how the distributor is already set up, and switching to manifold vacuum brings the advance in perhaps earlier than is desirable.
-Dave
sounds like a nice combo 
