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Vacuum advance recommendations and specs.
Vacuum advance control (VAC) recommendations and specs for '57 to '74 OE engines with full time vacuum advance and ported vacuum advance engines that are converted to full time vacuum advance.
NAPA part numbers listed.
All can be cross referenced at any other brand web site (BWD, Standard, Niehoff, etc.), however, I don't consider the Delco cross reference to be accurate. ID numbers (referenced in quotes) stamped on the mounting bracket should all be the same, regardless of brand, as they are all made by Standard Ignition Products, including those sold by Delco. Specs in crankshaft degrees at manifold vacuum. Some manufacturers' specs are listed in distributor degrees, which are half crankshaft degrees. Do not confuse the two.
VC1810 ("B28" 0@4", 16@8") - All SB with mechanical lifter camshafts, optional on L-79
VC1765 ("B20" 0@6", 16@12") - all SB with base engine camshaft and Powerglide, all BB, L-79, optional on base engine camshaft SBs with manual trans (Note: according to one reference the VC 1808 "B26" has identical specs, but I have not confirmed by testing one)
VC1802 ("B22" 0@8", 16@15") - all SB with base engine camshaft and manual trans.
Base camshaft engines are 283-220/230/245/250FI/275FI, 327-250/300, all 350 except L-46, L-82, and LT-1.
The above recommendations also apply to engines that have ported vacuum advance ('63 L-84, L-72/71) after they have been converted to full time advance, OE dual points distributor engines if the dual point is replaced by a single point VAC distributor, and emission controlled engines that are converted to full time vacuum advance from ported vacuum advance. After converting emission controlled engines to full time advance use the VAC recommended for the antecedent non-emission controlled engine. For example, the L-48 antecedent is any base camshaft SB. L-46 and L-82 antecedent is L-79. L-82 with Turbohydramatic should use the 8" VAC if idle vacuum in Drive is less than 13".
Before installation check that the VAC pulls the link to the limit at the specified vacuum plus or minus 1" Hg., and I recommend you take your Mighty Vac to the store and check it before you leave.
After installation on the vehicle check that total advance is plus or minus one degree of spec.
I have heard reports that boxes contain incorrect ID numbers for the part number on the box or the correct ID number parts do not meet specs.
For any other full time vacuum advance application use the following guideline based on idle vacuum in neutral for manual trasmissions, and in Drive for automatic transmissions.
less than 13" - use a 8" VAC
13-16" use a 12" VAC
over 16" use a 15" VAC
Increasing idle speed increases manifold vacuum. Keeping the VAC locked at full advance is a basic criterion for both idle stability and sufficient total idle timing to minimize fuel consumption and heat rejection to the cooling system.
Everyone print this out and keep one copy in your files and one under your pillow.
Duke -
Duke, Thanks for your excellent help, I saved it *NM*
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