Base timing. Really ?

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yellow rose said:
You should have the VA hooked to ported (timed) vacuum. It should not pull timing at idle
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In this case he might want to use manifold vacuum for V-can.
If his engine likes 20* his diz will add to much mechanical in its current state. So using manifold vacuum will allow him to set idle timing at 10-12* and his v-can will add more at idle then drop out as he accelerates until vacuum starts to build and bring the can back in .
 
THE way to do it right, well, here is this, the only way

Engines like to idle with between 20 and 24 INITIAL degrees, but don't like starting with that much lead.

So, how o get it right?

How about 14 initial? Well, not enough.

OK, lets fix it, we have the talent.

Build a simple degrees stop n the vacuum advance, and for say, 14 INITIAL, set the degrees stop to give 10 degrees, and plug it into full manifold vacuum. Stop the pin travel to set the degrees, DO NOT PUSH THE PIN INTO THE SPRING.

Engine starts a the conservative 14, vacuum builds, brings the v/a in, with the added 10 v/a degrees, IDLE is now 24 deg/BTDC.

Modify stop as needed. DO NOT USE PORTED VACUUM, a second accaleration advance curve isn't needed when the mechanical curve is correct for the application, it isn't for an EMISSIONS engine.

gmvacuumadvancepacket@gmail.com Works on other makes advances as well. Be creative.

Crane 99619-1 plate.jpg


GM advance Crane plate.jpg


GM stock vac adv stop plate.JPG
 
That works only if you have enough idle vacuum to pull the can in to its stop. Otherwise the idle rpm will be forever wandering and unstable...
 
I have run several engines with 284/484 (Hemi Grind) cams and I never had to run that much advance .
 
That's a pretty small grind though. I ran that cam in a basically stock '69 383 with a DP4B and 750 vac sec "back in the day" and it idled at 13", 650 rpm or so. Probably could have been tuned for more.
My current 312/.652 (272@.050) in a 451 wants even more idle advance than the 27 I'm giving it, but still only makes 8" at 1200 rpm. So I can't use the can to pull in more advance.
I do have it connected to manifold vacuum because the cruise is 15" and I drive it on the street most of the time. Doesn't have any effect on the idle timing. Also there's no ported vac on my current carb anyway :)
 
I dont remember as its been a long time since i checked it with a gauge, but if i remember right, it had quite a bit of vacuum at idle even with this cam. SO, tell me this..how are you all determining exactly how much initial timing your engine likes because some are saying theirs doesnt need much and some are saying theirs needs a lot..?
 
Cam specs and tuning. The cam you are running isa great cam but not really big . It shouldnt require 20
 
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