Welp, the shaker is out.......

[ratio411]

...there was a trick that used to be done in the 70's and 80's where only the rear of the plenum divider under the secondaries was milled down, generally it would be milled down about 3/4" or so and 1.5" lengthwise so that when you were only using the primaries the "notch" wasn't really doing much...

This is probably going to be considered useless trivia from someone who was around back then, but...

The rear portion of many intakes from the 70s were milled down under the secondarys like you describe, but not for any reason you would think. It is sorta neat to think that this is some sort of 'old school' trick that has been lost to time and we are rediscovering it... not so.
The reason that those notches were there was because Holley tinkered with and tried to market a 3 barrel carb during that era. It was supposed to replace 4 barrels... obviously it never did. The 3 barrel carb and the secondary notches faded away with time.
The secondarys on the 3 barrel, or secondary, was one single oval throttle plate, instead of 2 separate plates. The oval plate would swing open and need the notch in the plenum divider to operate. If there was no notch, the 3rd barrel could not open.
Externally the 3 barrel looked like any other 4150/60 Holley, the only difference was the back 2 barrels were fused together as one long oval.
My .02
Dave

Edit: More useless trivia... Holley and GM were so close during this period, ie. 780 vacuum was designed specifically for Chevy use at first, that GM put notches in a couple of it's hipo intakes from the factory. They anticipated either customers using the new wave 3v carb or maybe even going to it right from the factory in short order. Then emissions, insurance, and fuel shortages did what they did in the early 70s, destroying all those plans.

 

[bnickel]

that makes sense about the 3 barrell carb but i have seen dyno where they did exactly what is described to gain more airflow and in turn more horsepower from a 4 barrell. maybe someone discovered that after bolting a 4 barrell back in place of a 3 barrell. who knows but it seemed to work

 

[streetgrande69]

You know, I haven't really been following this thread, hell if I want to talk, I’ll just come over, and I did find some kind of interesting pics of a shaker set-up though............
shaker on a 65-66 link, kinda cool.........


don't hate if this has already been posted.

 

[bnickel]

hey eric, that is a really sweet setup you found there. very cool

 

[mustang70]

That is a nice set up there. It's really clean. I would want some sort of flapper though. I wouldn't want to chance water getting into the filter. Yes, I do plan on driving this thing in the rain.