3BBL

[69hemibeep]

I used a 950 in the early 70s, used a gear drive to the 3rd barrel and an accelerator pump adapter that put long squirters into the back barrel. It worked great.

 

[lewtot184]

I used a 950 in the early 70s, used a gear drive to the 3rd barrel and an accelerator pump adapter that put long squirters into the back barrel. It worked great.

I did the squirter thing with a 50cc pump. I settled on the original 30cc pump, .028 squirter and blue #427 pump cam. Thing drove very well.

 

[hacksaw]

I used a 950 in the early 70s, used a gear drive to the 3rd barrel and an accelerator pump adapter that put long squirters into the back barrel. It worked great.

thats what is on mine. with a gear drive deal to make it a full on everything at once deal.

 

[Michael_]

The secondary side was turned into an oval. Or more simply, the metal in between the two barrels was removed.

I prefer carburetors over fuel injection because of their simplicity and i have a basic understanding of how they work. But i'm far from being an expert.

That being said, what are the advantages and disadvantages of this 3bbl vs. the standard 4bbl design?

 

[lewtot184]

I prefer carburetors over fuel injection because of their simplicity and i have a basic understanding of how they work. But i'm far from being an expert.

That being said, what are the advantages and disadvantages of this 3bbl vs. the standard 4bbl design?

The advantage the 3bbl had was more venturi area giving more air capacity. Keep in mind this is mid '60's technology and double pumpers and dominators haven't arrived yet. Also, Nascar dictated single carbs.

 

[rumblefish360]

I prefer carburetors over fuel injection because of their simplicity and i have a basic understanding of how they work. But i'm far from being an expert.

That being said, what are the advantages and disadvantages of this 3bbl vs. the standard 4bbl design?

This is the only place I have ever heard of people limping the 3bbl carb, having successfully used them. All I ever heard was curse words after the words, “3bbl.”

As said above by lewtot184, this was someone ingenuity to get more cfm. The dominator was not on the horizon yet.
(Maybe, who knows?!?!)

You could make your own. I was in the process myself. But also wanted to add an extra squirted in the rear. I was able to drill straight through the body and then down to add the squirter. This leaves a tube to be pressed in and crossing in the middle of the oval area that needs to be cleared out. Making the butterfly’s into a single butterfly is easy with the correct thickness of metal. You can even remove some of the shaft or just make it thinner.

Once I have my garage built at the new homestead, I’ll fish it out of the boxes of crud I have and work on it again. Doing this mod is best suited for high rpm power. Opening up the secondary side to soon would not be an advantage for most applications.

A FWIW mention, some AFB and maybe AVS carbs are solid in the center while new models have a open space.

 

[rumblefish360]

Below, in order;

1; Carter Competition 625 AFB - 9636
2; A later year Carter Comp 625 - 9636
3; OEM Carter 4429
4; Edelbrock 1806 AVS

Notice the centers.

 

[lewtot184]

I think most of the 3bbl problems were people trying to re-engineer them. Thèy're best kept as designed. Back then folks were trying to "make" mechanical holleys. Most gadgets weren't very effective. I know I tried the gadgetry. Holley did start making mechanical carbs around late 60's but by then 3bbls were past their prime. Nascar had the race muscle but us drag racing kids never realized it. When Nascar banned multicarb this ushered in the single carb technology boom.

 

[Michael_]

I think most of the 3bbl problems were people trying to re-engineer them. Thèy're best kept as designed.

So if left stock are there any downsides compared to a regular 4bbl carburetor?
More air = more power but it's probably not that simple?

 

[12icer]

The 1050 I had did okay but I put it on where I had a 850 double pumper I had cut the choke tower off, put two rios on and spray tube orfice set them , hogged, zip tubed, vent baffled 4 corner jetted and put a 4.5 power valve in it with the 310 SS solid. It was like having coil springs launch from the stab, tried the 3 barrel and it went about 15 feet before the power really came on because of the vacuum time, I may have opened the vacuum channel up and used a lighter spring to make it hit quicker, but I just went back to the 850 and took the gas mileage difference on the road.

 

[lemondana]

Nick's Garage featured one on a 427 destined for a Yenko clone. Check it out.

 

[lewtot184]

So if left stock are there any downsides compared to a regular 4bbl carburetor?
More air = more power but it's probably not that simple?

So if left stock are there any downsides compared to a regular 4bbl carburetor?
More air = more power but it's probably not that simple?

A 3bbl is just a modified 4bbl. Same concept as any vacuum secondary holley. The problem with a 3bbl today is parts. The front half will use basic holley jets, power valve, and gaskets. The secondary side uses a unique metering plate and gaskets and the real issue is finding a vacuum diaphragm which is unique too. Keeping all the choke assembly helps the carb be a little more colder climate friendly. 3bbl's are just an attempt to put a race carb on the street. They really do drive well. I think one, with all the parts, would be fun on a ch4b. I still have my 3bbl, but needs parts, and a ch4b laying around.

 

[lewtot184]

The 1050 I had did okay but I put it on where I had a 850 double pumper I had cut the choke tower off, put two rios on and spray tube orfice set them , hogged, zip tubed, vent baffled 4 corner jetted and put a 4.5 power valve in it with the 310 SS solid. It was like having coil springs launch from the stab, tried the 3 barrel and it went about 15 feet before the power really came on because of the vacuum time, I may have opened the vacuum channel up and used a lighter spring to make it hit quicker, but I just went back to the 850 and took the gas mileage difference on the road.

I tried light springs too and they don't work. No kill bleed means the secondaries flop open without a stiff spring.

 

[rumblefish360]

So if left stock are there any downsides compared to a regular 4bbl carburetor?
More air = more power but it's probably not that simple?

Here’s my take on it. Despite what I have personally heard and read here.

I’ll start by saying, “You are correct!” It isn’t that simple. The added area of the secondary side is now massive and hard to make work nicely unless you have a heck of an engine underneath it that the overall size of the carb is just right to small in size for the engine. Also remember there is no secondary squirter.

Now if your engine is big enough to consume a sudden wide open throttle with the 3bbl., consider it probably undersized. Otherwise, it’ll need a high converter flash, steep gears, etc….

Now I’m sure a drag racer that’s been around the block a few times will tell you that if the car does t act well on a full stomp of the gas pedal that you just need to govern your right foot a little slower until the engine catches up so it can use all of the carbs open area.

Also, this carb will show itself up top in the rpm range. Like any other bigger carb would.

 

[PROSTOCKTOM]

I have very nice 950 that I can post some quality photos of tomorrow for viewing.

There are super fun to use and like a QJ or Thermo Quad they sound great when the secondaries open up.

Tom

 

[rumblefish360]

I have very nice 950 that I can post some quality photos of tomorrow for viewing.

There are super fun to use and like a QJ or Thermo Quad they sound great when the secondaries open up.

Tom

I bet! Muha ha ha ha… It has “That SOUND!!!!!”

Could you tell me the area or at least the dimensions of the secondary side?

 

[PROSTOCKTOM]

I bet! Muha ha ha ha… It has “That SOUND!!!!!”

Could you tell me the area or at least the dimensions of the secondary side?

The secondary blade is 1.75" x 3.4025"

Tom

 

[PROSTOCKTOM]

Tom

 

[lewtot184]

3bbl's have about 8.1sqin's of venturi area. That's a lot to feed on one accelerator pump. This why tuning the secondary opening rate is critical.

 

[33 IMP]

I thought the three barrel vacuum pod used the same size diaphragm as a Sixpack two barrel. Am I wrong?
And yep, getting the third barrel working right on your car was the secret, and the three barrels downfall.