VintageMopar wrote:
There are 3 options for vacuum advance sources. Ported, manifold and Venturi.
Ported is zero at idle and goes up as engine rpm increases so dist advance increases with rpm, usually desired as long as detention /pinging doesn’t occur.
Manifold vacuum is high at idle, drops with rpm so all your advance is at idle and drops with speed. Better launch and low speed performance but not at highway speeds. A lot of cars we’re plumbed this way.
Venturi vacuum is similar to ported but slightly different rise. The thing with it is you have to use a vacuum amplifier as it is too weak a vacuum to actuate advance directly.
Thank you, I was really hoping you'd chime in.
As you implied, really depends on how you're going to use the vehicle. For mostly around town, one way is best. Mostly highway? Another way is best.
Thank you also for mentioning venturi vacuum ... I overlooked that, in part because most vacuum ports originate below the throttle butterfly.
I try repeatedly to warn people: Pay attention to the context of what you're reading and advice you're getting. If you're using race car advice, you're probably (strike that, definitely) going to be dissatisfied when you're cruising the strip, profiling for spectators. Likewise, if you're following daily driver sedan advice, you may be less than satisfied when it comes to your heavy truck. (Hint, hint -- motorhome.)
