Holley baseplates

[Kurt S]

I have 3 Holley baseplates with the squared off corner. What were these originally used on?
#1 and 3 have 172 throttle plates. #2 had 109 and 311 plates.

#1 & #2 have side mounted PCV.
#1 has a small rounded boss and hole on the left side and a port on the lower right mounting boss.
#2 has an extra unused vacuum boss at the bottom, both right side mounting bosses are slight different than #1, extra hole by bottom left mounting boss.

#3 has rear mounted PCV and looks similar to #1 except the PCV and the boss & hole on the right side.

What's mounted in the very center of #2? The other 2 have a hole there.
What models got the squared off mounting boss?

Thanks!

[VintageMusclecar]

#1) Early GM 780 vacuum secondary, later service style as evidenced by the thicker corners.

#2) Over-the-counter 600 cfm emissions style carb. The hole in the center is a restricted vacuum feed. Might be off of a 6619 or similar carb.

#3) Appears to be from a 3310-1 carb--the blank boss at the pass. side rear can be drilled for a side style PCV like the original GM bases were. Some rebuilders/restorers modify these bases by cutting off the PCV tube boss on the rear and welding the hole closed, then they drill the side for the PCV. The right front corner can also be drilled for ported vacuum.

[ZLP955]

Eric your knowledge of Holley carbs is always impressive.

[Kurt S]

Were the square corner baseplates used for GM applications?
Asked another way - Why did Holley use a square corner baseplate?

What was the little rounded boss on the left side of #1 for?

Lastly, when did Holley switch to 4 digits? I thought it was 71, but I have a carb dated 244.

Thank you Eric!!

[VintageMusclecar]

AFAIK, the square cornered bases have a notch cast into them for a throttle cable bracket locating tab.

Rounded boss on #2: Not sure.

Generally speaking around 1971, but I have seen several 3 character carbs dated with a #2 prefix as well. I honestly don't know the reason for the apparent overlap.

I could elaborate on a few other anomalies as well, but I won't because that would help the re-stampers better hide their work more than it would inform potential customers of the deception.

Thank you Tim, and happy to help Kurt.

[Kurt S]

Thanks Eric!!

[69 Post Sedan]

From what I've seen, the notch on the baseplate was for the throttle cable bracket was for Chevelles with a cable throttle, which I believe started in 1969.

If you see one without the notch, that is for a early 1967-1969 Camaro and 1968 on up Nova as they're throttle was a rod so it didn't need the notch to hold the bracket.

I'm not sure when or even if the Nova ever went to a cable throttle.

Kurt

[L78steve]

Yes Nova went a cable in 70. 69 on the 6 cyl.

[Kurt S]

Everything went to cable in 70 due to linkage binding issue liability.

I looked at an original of #1 and see what you mean. Thanks!