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View Full Version : Vacuum advance, how much is too much?



Rosstude
10-07-2005, 10:53 PM
Well, it looks to be a vacuum advance kind of day. I just installed a Delco window unit, and picked up a vacuum advance can at the local parts house. It has a "22" on it, and my timing light tells me this is 22 degrees. The manual shows 16 degrees at crank. I (re)set the initial timing at 5 degrees, which is where I set it previously by the advance it until it pings, then back off 2 degree method. I ran with the new dist about 10 miles at speed, no pinging.
Any experience out there on this? Should I look for an 16(8)degree can?
I know there is (in some cases) some milage to be had in increasing the vacuum advance, and I am tempted to try it out.

Ross.
57 Provincial
58 Transtar
66 Wagonaire

bige
10-08-2005, 08:47 AM
Get an adjustable one from a High Performance supplier, you can adjust the degrees and how quickly it responds.

R2 R5388

curt
10-08-2005, 07:08 PM
When is the vacuum advance most advanced, ldle,and highway speed on the flat level ground? I assume the advance is directly proportional to the vacuum, lower vacum less advance. Should a car just timed with the vacuum disconnected have the timing advance 16 degrees when the vacuum advance is reattached? I have never noticed that.?[?]:)[?] I know how it is advanced but I seem lost as to when it should be most advanced. Does the mechanical advance work with and aginst the vacuum advamce?[?]

Rosstude
10-08-2005, 10:22 PM
The vacuum advance is connected to a "ported" outlet on the carb, that is, on top of the butterflies. It sees vacuum only when the throttle is open, and it takes a set amount of vacuum (like 12") to pull it in. As such it kicks in at highway speed, and drops out at WOT to avoid pinging, and is not in at idle because the butterflies are closed. Disconnecting it when setting the timing is most often recommended, but not needed IF all things are adjusted right.
The mechanical advance, is a centrifugal advance, and starts to come in just above idle (like 800RPM) and is all the way advanced at a given RPM (like 1800RPM) It works with the vacuum advance, although it is a seperate device.

I will be making a road trip of about 200 miles tomorrow. I will monkey with the timing along the way if it pings. I may go with the adjustable vacuum advance later. I have one on my slant 6, and it really allowed at lot of vacuum advance, but the ability to adjust the inches it pulls in at. It took a lot of trial and error to keep the ping out, but I gained 4 miles to the gallon. I was hoping someone out there has done some experiencing with this.
Later.

Ross.
57 Provincial
58 Transtar
66 Wagonaire

bige
10-09-2005, 12:21 AM
Usually there is a cam flat cam in the kit that allows the adjustment of degrees also. It limits the amount of breaker plate movement. Static timing needs to be adjusted after it's installed. I have one on the Delco on my Avanti.

R2 R5388