Edelbrock AirGap question

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canyncarvr

canyncarvr

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I remember in the old days we used to notch the divider in the LD340 manifolds; a small notch helped stabilize the idle vacuum signal and a larger notch helped the midrange a bit.
No idea why Edelbrock has one on the Chevy AirGap, but not the Mopar unit though.
 
Thought it was for a Holley 3 barrel to open.

IMG_20231015_194630.jpg
 
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rumblefish360 said:
Just as a side note addition, Carter also did this to their AFB/AVS but I don’t remember which one at the moment. A short lived carb, both of them.


And then…. They realized a power improvement…..
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I'm not arguing, because the good lord knows I ain't seen it all, but I've never seen that in print from a competent source in any publication. Ever. All I've ever read and heard was that the notch was there for the Holley 3916 and 4604. I had a 3916 several years ago and sold it like an idiot.
 
The honest and true back story of its actual history I can not confirm. However, the “How to” Carter book has a 3 barrel carb pictured and stating it was for the Pontiac racing effort.
 
rumblefish360 said:
The honest and true back story of its actual history I can not confirm. However, the “How to” Carter book has a 3 barrel carb pictured and stating it was for the Pontiac racing effort.
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Yes, GM used them pretty much exclusively, I think. I've heard from several local "old guy" sources that Chevrolet used them straight from the factory on some things, but I've never been able to verify that. What IS verified though is, they WERE used on the Baldwin Motion cars. But those were modified by the Baldwin dealer, although they were still new. I don't "THINK" Ford or Chrysler ever used either version.
 
Really? Baldwin Motion used them? I didn’t know. Ya think I would growing up down the road from them. But then again, I’m kind of young…..
 
RustyRatRod said:
I'm not arguing, because the good lord knows I ain't seen it all, but I've never seen that in print from a competent source in any publication. Ever. All I've ever read and heard was that the notch was there for the Holley 3916 and 4604.
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It was in the DC engine manual, for one. I believe it was in Shepard's book, too- can't verify, loaned it out and hasn't found it's way back yet...
 
Professor Fate said:
It was in the DC engine manual, for one. I believe it was in Shepard's book, too- can't verify, loaned it out and hasn't found it's way back yet...
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The “Notch” at the rear or just simply in the plenum center divider wall I don’t remember in ether book.
The “Center divider” mod where the books say to mill it to 3/8 wall height and round the edges I remember.

This is where I remember reading that, between the lines reading was useful. It’s basically a legal cheat. The rules at the time in several racing arenas said you “MUST RUN A DUAL PLANE INTAKE MANIFOLD” rule was in effect and this was MoPars answer to us on what to do if you had to run the dual plane intake.

I did it to a LD-340 years back and it was quite helpful. I also ran a 440 TQ on top.
 
A friend of mine bought a 69 396 Chevelle and had Motion tune it up for him. He said it made a tremendous improvement in it running, but with other problems with the car didn't keep it long. Don't remember a lot of what they did, they rejetted the carb and probably recurved distributor. Back then we had all to do to make car payments and insurance so not much left for hopup mods. $3000 - 3500 for factory muscle car made it affordable for those of us not too well endowed with money. I bought my 68 Road Runner while still in the service, paying $90 a month for it and making $180 a month.
 
Went through all old DC and Shepard books. They all state the notch was for performance improvements on Mopars determined by dynamometer results. LD340's came with the notch when I bought them. Rounding the leading edge was required
 
Professor Fate said:
It was in the DC engine manual, for one. I believe it was in Shepard's book, too- can't verify, loaned it out and hasn't found it's way back yet...
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I sure don't remember it. I've had every edition too and still have the latest. I'd say I'd dig it out but I'm too lazy for one and I take your word for it.
 
Intro page in this chapter and the LD340 page with instructions. These mods were all done using dynamometer tests as per intro. Shepard book goes into more detail if needed. Looks like the wall is removed but shows notch was there before hand in this Figure

DC intake1 001.jpg


DC intake2 001.jpg
 
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