I am trying to get correct timing and advanced timing set up on my 396 Camaro . Barry Grant speed demon carb suggests initial to be 14-16 degrees to get proper signal. I am turning distributor to get that initial, but my distributor is a 24 degree advance unit, which adds up to 38-40 degrees advanced. Can I adjust my vacuum module in or out to take some of the advanced timing out? I would think 36 max to keep pinging away. I am trying to tune my car as close as possible before I put front end sheet metal on, so I have not driven car yet. Any suggestions?

396 bored .030
10.58 to 1 compression
274 comp extreme hyd.roller
Edelbrock 60459 heads
Edelbrock air gap

Your distributor owners manual should tell you which way and how much each turn will take out. Mine adds or subtracts 2* of advance depending on which way you turn it.
Say your dizzy is set at 14* initial (what you see at idle) and the advance comes in, and then the vacuum advance comes in at cruise.
38-40 is not bad, any lower on the initial, 14-16 you said and it won't run very good, big cams respond better to more idle timing.

It sounds like you may be confusing vacuum advance and mechanical advance.

Vacuum advance is not part of the equation when determining / setting initial or total timing, the vacuum hose should be disconnected and plugged for those tests.

If your distibutor is giving 24 degrees mechanical advance, you will need to reduce that to get what you need. What kind of dizzy is it?

An adjustable vacuum advance is adjusted by sticking an allen wrench thru the hole where the hose attaches and turning a screw in there. This changes the spring tension inside, and it will change how much vacuum it takes to produce full advance.

That adjustment will not change how much advance the can puts in.

It`s a mallory hei street distributor. That`s what I thought Jim, but I read a post leading me to believe the allen screw in the end of the vacuum advance port adjusted a stop to control the amount of advance. That just sets tension on advance to control when it comes in, right? Mallory instruction sheet says to turn clockwise for more advance and counter clockwise for less,that is a little confusing too?The amount of advance is controlled by bushings and springs in the mechanical advance, right?
Do you guys think I will be ok if I left it at 14 degrees initial with vacuum unhooked, and 38 degrees fully advance at around 2800-3000 rpm with vacuum hooked up ?

Gary never try to set your timing with the vacuum advance hooked up. If you do you'll never get things under control. The vacuum advance supplements the mechanical advance. It sounds like you have an adjustible vacuum can on your dist, don't factor vacuum advance in until you have set the total. Let's say you set total to 36 degs and there is 24 built into your dist. Your initial will be 12 degs, I think your dist has a feature that lets you change the amount of mechanical built in but for now leave it at 24...

So lets roll with 12 initial, 24 mechanical for a total of 36 degs at 3000 rpm. Now hook up the vacuum advance to a manifold source. Check your idle timing and total timing to see what the vacuum advance added. For sake of this discussion lets say it added 10 degs across the board. Your engine is now getting 12 degs as it's started, 22 degs at idle, as much as 46 during part throttle and it will drop off to 36 as you go WOT. That's very liveable and your engine may actually like more vacuum advance but until you can get out and drive the car you will never know.

Use the adjustible vacuum advance to fine tune the timing for street drivability... Some adjustible vacuum cans change the amount of vacuum needed to pull in the advance others actually let you adjust the amount of advance... Play around with yours to see exactly what it is doing.