Help me time a SBC

As I understand it I should have between 32 and 34 degrees BTDC with full advance on a mildly tuned 350SBC. Is that right?
I contacted Prestolite and they said my Accel dist has 22 degrees mechanical advance at 3100rpm and that the vac advance is adjustable.
I'm thinking that I can check where my timing is now and then hook the dist to manifold vac and see how much it changes to see what the vac advance is set at on the dist, then if I back out those figures it should give me my timing number with the vac plugged at idle, correct?
For example if the dist has 5 degrees vac advance and the mech advance is 22 that gives me 27 total so my timing should end up at 5 degrees BTDC.
Or if there is 10 deg vac advance plus 22 mech, I end up setting it a 0 degrees.
Does this sound right?

 

Sorta. Rev that thing up to 3100 and set it at 30-34 degrees. Then see where its at. probably 8-12. Then plug in the vac advance and set that thing to as much as it can take by trial and error but you might see around 20 at idle.

 

Check out my thread on timing my SBC. Take a look at the post by "HOOP". I think he chimed in on page 2 or 3. He got me dialed in and my car runs like a raped ape and I'm pretty sure my MPG is improved. I haven't even checked it yet.

http://www.jalopyjournal.com/forum/showthread.php?t=804546

 

Here's what he wrote in my other thread on it.

<TABLE id=post8953531 class=tborder cellSpacing=0 cellPadding=6 width="100%" align=center border=0><TBODY><TR vAlign=top><TD id=td_post_8953531 class=alt1 style="BORDER-RIGHT: #e5e5e5 1px solid">If you have a distributor with mechanical advance, pull the cap and twist the rotor in the direction of rotation, it should move 10 - 18 degrees in that direction and snap back freely. If not investigate and free up.

While you need a dyno or some road testing to get the last bit of power/economy, we know the typical SBC to get you very close.

A stock HEI has 20-22 degrees of advance but it usually comes in pretty late.

To check for 36 degrees we need a marked damper, a timing tape applied to the damper, or a dial back timing light.

If you find the advance comes in too high slip over to a parts store and buy a spring kit. Put lighter springs on until the advance is maxed at 2500 - 3500 RPM.

Set the advance to 36 there and and whatever your initial is is fine.

If you have a high compression engine and get starter kick back you will need to add advance in the distributor.



Here is a good guide.

http://www.pontiacstreetperformance....distcurve.html

Once you have the total you need to setup vacuum advance, you want a unit that allows max advance at about 2 inches less than your idle vacuum. Oh and for SBC with these kind of advance numbers run manifold vacuum to the vac adv,

Advance will usually work out with 14 -18 degrees vacuum advance.

The VC 1838 has 14 degrees crank advance at 10-12 inches of vacuum so it works with Fred's 16 initial to give us 30 degrees at idle.

If you get an adjustable vacuum advance you can use a mytivac and adjust it to 2 inches below idle vacuum to start.

If you use an adjustable vacuum advance be sure to get an advance limiter plate.



You can set the limiter to achieve 24 - 32 degrees advance at idle.

If you are 12 initial, 16 would put you at 28.

If you get sustained ping at part throttle run less vacuum advance, if you get transient ping on tip in and upshifts go to a higher vacuum.

Simple eh?
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You can run 38º to sometimes 42º (depending on gas quality, blend, altitude etc,) mechanical advance at that 3100 RPM,
PLUS another 12º Manifold Vacuum advance.
So, if the distributor has 22º you can set the at-idle timing at 14º± and then hook up the vacuum advance.

That's right, 38º plus 12º is 50º
but when you open it up the manifold vacuum disappears and that 12º goes away so it won't affect it. Now if it doesn't ping under a load but does ping while just cruising down a level highway at high RPM you might want to take some of the vacuum advance degrees out, a little it at a time. My Chevy does that on California "winter gas blend" sometimes. I fix it with some gas from the higher octane pump.

 

Thanks guys. That helps a lot!
Between getting the timing figured out and getting my Qjet back from Bob Jennings this thing ought to run like a striped a$$ed ape when I get her back together.