vac. advance vs. initial timing

[jefferias]

simple question i think?  to get the most performance,effiency, and fun to drive factor- do you want to use the most initial advance you can without "pinging", or compensate with vac. advance. this is regarding 1/4 to 3/4 throttle. i have my initial(BASE) at 9degrees and vac advance adding maybe 13 degrees at idle.(guessing cause i only have a crappy timing light) i have read lots of guys use a pretty high initial timing compared to me.( i know that there are plenty of variances to come up with right timing for a particuliar set-up)  any thoughts?

[Captkaos]

You want to use the most initial you can that makes the motor run the best.  Generally this is 10-12 on a SBC.

[Blue 82]

You forgot to mention mechanical timing
add another 20/24 degrees of mechanical to the equasion
the tricky part is to get the rate of advance correct for your application

Just adding more initial to make it run better is OK
but to get the most out of it you can tweak em with not much time/effort and $$$

http://static.summitracing.com/global/images/instructions/acc-9102%282%291.pdf

[jefferias]

my mechanical is bang on 20 degrees from the dizzy. ive already re-curved the dizzy with 1 light and 1 med spring. tried couple different combo's with springs and i like where its at right now. left the 23 degree weights off and kept the stock 20 degree in. (new msd streetfire setup)  will try to advance more with the initial and let cha know what happens. 

[Blue 82]

does it have the adjustable vac advance like the accell unit?

[jefferias]

yes it does have adj vac advance

[jefferias]

k well changed my initial timing from 9 to 11 degrees. lowered my vac advance to about 22degrees when running at idle. also leaned out mixture screws a bit to smooth out idle. well the temp dropped about 30degrees celcius today and the truck after work today, was to say the least, is not runnin good like (jusy on start and warm up) before. my guess is that cause of how cold it got i probably got a "lean situation" so im gonna richen it up a bit and see what happens b4 i start playing with timing again.

[jefferias]

well today i put the mixture screws back to where i had always had it set. cold today again and after work started right away let it run for about 5 mins and attempted to go home.  it stalled twice ( which doesnt happen hardly ever) then just revved for a bit and went upon my usual business. i am now gonna try to add a lil more advance at the dizzy and see what happens.  i think my biggest problem is myself being to picky or maybe expecting a bit too much? haha 

[Rib Tickler]

Is that adjustable vacuum advance only on aftermarket distributers? cause I never heard of adjusting the vacuum advance I thought you could only change your timing by turning the distributer and playing with springs and weights.

[SUX2BU99]

Some adj. advance vacuum canisters have a small allen-head screw in the center of the vacuum port. I can't recall though if it adjusts rate of advance or the RPM that the advance kicks in.

Is there a good online "for dummies" guide on how to measure, set and change the timing (base, mech. and advance)? If there is I'd buy a timing light and check all this stuff out. I bought a truck like this because of the carb'd, HEI, SBC for it's incredible simplicity and ease of tuning......but I don't know how to tune it yet  LOL  I've just played around with twisting my HEI for power gains and when I hear pinging in this colder air, I put in higher octane gas. WHen it pings on 94 octane, I know it's time to back off the distro

What's kinda interesting (to me anyway) is before my cam and head swap, I couldn't ever get it ping no matter what (not that that is a really bad thing but to me it just showed I had a pretty mild setup or wildly rich carb). I would use 87 octane gas, hot air or cold air, distro advanced to the point where power would drop off and not a sound. Now with my cam and head swap, it actually started pinging some when I would play with my distro. My old heads had 76cc chambers and my new ones have 72cc so it's a little higher compression but not like 64cc heads would have.

[78 Blazer]

  Accel HEI distributors have a adj. vac. advance that controls the RPM the advance comes in at. A little sooner or later.  Summit sells Accel adj. vac. advance units to upgrade your stock distributor. Accel units have the allen screw inside that you turn one way or another to set your advance. 

  I have a Mallory HEI distributor that claims to have a adj. vac. advance but it don't have the allen screw in it. I haven't figured out how to adjust it yet. My 383 is running good but I really haven't had time to play around with the timing much yet. It's 10.3-1 compression with 93 octane gas. My timing is set at 35 degrees total all in by 2800 rpm. 15 degrees initial and 20 degrees centrifugal.
  Does anyone know how the Mallory HEI adj. vac. advance works without the allen screw that I'm used to in the Accel units?