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
 
tonysrt said:
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.
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Hey Tony... do you recall what your friend paid for a tune up?

I do not want to dive into doing one on my own. I have a local mechanic that's good and honest (hard to find now-a-days) and I would like him to do the tune up. I understand that the cost depends on how much needs done. I'm thinking the following: plugs replaced (wires are fine), points, distributor cap, timing. Depending on the condition of the carburetor, maybe have it serviced. The entire (rebuilt) motor only has about 12,000 miles on it. Everything looks brand new! I was just trying to get a ballpark figure. It's a 1972 Duster 340. Thanks!
 
You realize we're talking about 54 years ago. He was in the electrical union so money was no object. He never told me what he paid and they pretty much only did Chevy's back then. My 68 Road Runner was running great, especially after I beat a 427 full size Chevy, so being in the Service I had no extra money for real tune ups like he got. I also had a 71 Duster 340 Auto and put in the electronic ignition, Direct Connection, back then, from single points, really woke that motor up. 4 years later I was kicking my self for selling it. Still do today.
 
Tony, when we met years back for some parts, you sure don’t look that old! Certainly fooled me! LMAO! Keep up the good work.

We all have a car or two….. or three… LOL… that we wish we still had. I could name a few for sure.

I’ve always liked the electronic conversion kits way better than points even though many cars of mine had points and ran just fine. It’s just after the years of service, the distributor gets a little old & wonky sometimes.

@Cudafever I don’t know why the Chevy has it and the MoPar doesn’t. I’ve also notice this. I think the Chevy needs it. You could try a small spacer to see if you get anything or any where. A cheap 1/2 (?) spacer is quick and easy. I wouldn’t cut the intake until I could prove it to myself it’s worth the effort.

Simple enough to do with the right tool at home.
 
rumblefish360 said:
Tony, when we met years back for some parts, you sure don’t look that old! Certainly fooled me! LMAO! Keep up the good work.

We all have a car or two….. or three… LOL… that we wish we still had. I could name a few for sure.

I’ve always liked the electronic conversion kits way better than points even though many cars of mine had points and ran just fine. It’s just after the years of service, the distributor gets a little old & wonky sometimes.

@Cudafever I don’t know why the Chevy has it and the MoPar doesn’t. I’ve also notice this. I think the Chevy needs it. You could try a small spacer to see if you get anything or any where. A cheap 1/2 (?) spacer is quick and easy. I wouldn’t cut the intake until I could prove it to myself it’s worth the effort.

Simple enough to do with the right tool at home.
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When I married my wife, she had just bought her first car (a 69 Charger 318) from her mom. I replaced the points for her and said that would be the last time I would ever do that. The distributor was in the back of the engine and was really hard to get to. I replaced her points with the DC kit and never looked back. Points may have been simple, but you had to almost be a contortionist to service them!
 
Ricks70Duster340 said:
When I married my wife, she had just bought her first car (a 69 Charger 318) from her mom. I replaced the points for her and said that would be the last time I would ever do that. The distributor was in the back of the engine and was really hard to get to. I replaced her points with the DC kit and never looked back. Points may have been simple, but you had to almost be a contortionist to service them!
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That was one of my reasons as well. Ugh! And I was young then! LOL!
While there is nothing wrong with points!, it’s when they get old and coupled with today’s junk at the stores, it’s more of a PIA to have a sweet running old machine running the OEM equipment.

I’m had a cam so worn out on one distributor, my buddy walked over and asked how the hell did he drive over here on that junk.
I just shrugged my shoulders and swapped out parts.

That was one happy car owner I’ll tell you that.

I kind of kid the old days when I was doing the mechanic work. Nothing like a blown away happy customer exploding on how nice there car is running and the missing power
(plus some - distributor twist trick…) has returned.
 
To add another point, pun intended, to the discussion. I had a 55 Chevy with a 265 and 3 speed stick. It would foul the plugs and run bad. I put a dual point mallory distributor in and it cured my problem.
 
tonysrt said:
To add another point, pun intended, to the discussion. I had a 55 Chevy with a 265 and 3 speed stick. It would foul the plugs and run bad. I put a dual point mallory distributor in and it cured my problem.
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Goooooood distributor!
 
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