from my install instructions with adjustable advance
set the base timing to 8-10
as delivered mech is 24 @ 2800
as delivered vacuum is 14* @ 12 Hg (4 turns)(8 turns possible)
"If surging or pinging is noticed at CRUISE rpm's turn the vacuum adjustment conterclockwise"
If more advance is needed turn clockwise
from the chart table for 1,2,3, etc turns with manifold vacuum
1 turn=3 deg all in by 11Hg, starting at 8Hg
4* turn = 14 deg all in by 12Hg starting at 6Hg, (45deg slope)
8 turns = 28 deg all in at 17Hg but a long slope starting at 4Hg
The vacuum advance is off when you floor it, the Hg is below 6, timing advances only from the mech to the 34 total.
When you back off the gas, as the Hg builds, the vacuum advance works against the mechanical for a smooth transition back to base timing
Your balancing motor load (Hg) to mech advance at any rpms for best burn possible.
Reason I bought it (and tuned both mechanical and vacuum): I can burn 87 octane with 10deg base/36 total (in at 2400) with no ping because of the vacuum advance. It replaced a Mallory dual point mech only that wanted 93 octane at 12 and 32 total
So jealous, you Chevy guys can buy just the adjustable vacuum, I had to buy a distributor.....
Last edited by red65mustang; 01-04-2005 at 08:44 AM.