[SD421]

Originally Posted by Kenth

1966 #1111090 389 2-bbl distributor has exactly the same centrifugal timing advance as the 1966 #1111078 389/421 4-bbl distributor.
0-4°@960rpm, 12-16°@2000rpm and 20-24°@4600rpm. Add to that 6° initial.

They do use different vakuum advance though.
090 uses the #1116242 control, starts@6-8in/hg and provides max 20°@13-14,5in/hg.
078 uses the #1116243 Control, starts@8-10in/hg and provides max 20°@15-17in/hg.

My 1966 GTO Shop Manual shows different info.

Dist# 1111078 is for a 389 4-barrel
0-2°@480rpm, 6-8°@1000rpm and 10-12°@2300rpm.

Dist# 1111054 is for the 389/421 Tri-Power
.5-2.5°@450rpm, 8-10°@1150rpm and 10-12°@2300rpm.

Vacuum Advance Model #is:
1116243 for the 4 barrel
starts at 8-10
full advance 15-17
max is 10 degrees

1116172 for the Trips (tripower)
starts at 8-10
full advance 14.75-16.75
max is 10 degrees
Don

BTW Wild about Cars has a great website where you can download the manuals for free
(you do have to register). Great source of factory lierature
http://wildaboutcarsonline.com/cgi-b...=9940395242400