informative article on GM vacuum advance units.
http://www.corvetteforum.com/techtip...=115&TopicID=3
I used information here to pick a vacuum advance for my 10:1 455HO, also running on 93 octane fuel. I'm running 10 degrees intial lead, and my mechanical advance adds 22 degrees of lead - all in at 2700 RPM for a total of 32 degrees lead. The vacuum advance I picked adds 16 crankshaft degrees of lead, all in at 8" of manifold vacuum. I'm sending my distributor to Rocky Rotella for "blueprinting", and he is also going to limit the vacuum advance down to 12 crankshaft degrees to help with some very slight transitional part-throttle spark knock. I do have it running to a manifold source to assist with idle quality. My cam is a Bullet flat-tappet solid grind, with a duration of 232/235 degrees @ .050, and .540"/.567" NET lift using HS 1.72:1 roller rockers (including valve lash).
My setup is a 4.200" bore 455 (467), ported 7F6 heads, 10:1 JE pistons (small dome), 455HO intake, SD Q-Jet, R.A.R.E. 2.45" outlet SD exhaust manifolds, Tom Hand designed and FullBore manufactured prototype single transverse muffler exhaust system with mandrel-bent PYPES X-pipe system to the muffler, GM L88 torque converter (2700 RPM flash), 3.08 gear, etc. The car weighs 3910# with me in it.
Driveability is excellent. Performance to date in my sig below.
Hope this helps some!
Later,
"455HO" Lloyd
1972 Formula 455HO; Lucerne Blue; 12.96 @ 104 MPH @ the '03 PSN's; 12.50's or bust this year!
1970 GTO 455HO; Palomino Copper
1972 GTO 455HO; Sundance Orange