What a Six Pack is on a 440 Mopar Engine

There are certain phrases used in the muscle car world and the legendary Six Pack is one of them. Some people aren’t exactly aware what it means. Let’s answer, what is a Six Pack on a 440?

A Six Pack on a 440 refers to the carburetion on a Chrysler 440 cubic inch displacement engine, produced from 1969-1971. The Six Pack consists of three two barrel Holley carburetors. The center carburetor is rated at 350 CFM, and the two outboard carburetors are rated at 500 CFM each.

This article will explain how each carburetor function, how they open up, list numbers and the differences between the center and outboard carburetors. Some of their facts may surprise you.

The following specifications and facts were learned from my personal experience and research, Mopar engine manuals, webinars, books and articles. I personally owned a 440 Six Pack which was on my first car.

A Six Pack on a 440

Any Mopar enthusiast will agree the 440 Six Pack is a legendary engine. Some will even put it up there with the all mighty 426 Hemi.

Both engines had the same torque, and the Six Pack made it’s power earlier in the RPM range. For this reason it could take the Hemi off the line and hold its own at the start of the race.

While Six Pack is the carburetor setup on a 440 engine, the words are also slang used when referring to the Mopar 440 engine with three two barrel carburetors.

Therefore, the words may refer to the carburetor setup on a 440 or the 440 Six Pack engine.

In addition, if you have a 1970 Challenger T/A, the words may refer to the 340 Six Pack engine under the hood. That’s a topic for a different article, as this one will focus on the one installed on a 440.

Technically, Six Pack is the wording used for a 440 Six Pack in a Dodge. The same carburetors and engine were also produced and installed in Plymouth cars. These identical carburetors and engines were then called a 440 Six Barrel.

For the purposes of this article, when I refer to Six Pack, I’m including the Six Barrel also since they are the same thing.

The first year for the 440 Six Pack was in 1969 installed in the limited production A12 Plymouth Roadrunners and Dodge Super Bees.

It was offered on more models in 1970 and 1971. If you would like to find out exactly what cars the engine was available with, check out my article, Cars With a 440 Six Pack From the Factory. In that article find out about the few Six Pack cars which snuck out of the factory in 1972.

Carburetors

If you’ve ever seen three two barrel carbs sitting on top of a 440, it’s like staring at gold jewelry. Some Mopar people will just stare mesmerized. I would often do just that with my Six Pack.

It’s a beautiful sight to see. All three carburetors are made by Holley from their 2300 series carburetors. In total there are 1,350 cfms:

Center carburetor: 350 cfm
Front carburetor: 500 cfm
Rear carburetor: 500 cfm

The three carburetors sit on top of the intake manifold inline, one behind the other. Three carbs and 1,350 cfms sound like a lot, and it is. Although two barrel carburetors are rated differently than four barrel carburetors.

Therefore, the total cfms are not the equivalent of a 1,350 cfm 4 barrel carburetor. If you do the math and figure the conversion, the 1,350 cfm is approximately equal to having a 954 cfm four barrel carburetor.

Even though, it’s still a good amount of air. You may be wondering why doesn’t the car bog when the gas pedal is punched to the floor and driving around at part throttle.

Cruising Around

A common question asked, how does a Six Pack carburetor work?

While driving around at normal acceleration the Six Pack middle carburetor is the only one opened. The outboard carburetor butterflies stay closed.

The outboard carburetors will open from vacuum under heavier throttle and higher engine rpm. The outboard carbs do not open from linkage. This is because the outboard carburetors are vacuum operated.

Full Throttle

Even under full throttle, the outboard carburetors don’t fully open instantly, but they get there quickly.

The outboard carburetors openly gradually, but quickly. So it doesn’t take long for all six barrels to open fully, but the moment the gas pedal is floored, all six barrels are not fully open.

The outboard carburetors open or close simultaneously. The engine operates either on two barrels or six barrels, but never on four barrels.

If you want to see how it operates under full throttle, the car in the video has a camera mounted in the engine compartment.

There are multiple times you can see the carbs and linkage in action. The close up video shows exactly how the outboards open under full throttle and how quickly.

Oh, did I mention the driver did one hole shot after the other? It’s a must see video in more ways than one.

See the Six pack linkage in action from a camera in the engine compartment.

Differences Between the Center Carburetor and Outboard Carburetors

The center carburetor has an idle adjustment screw. The outboards don’t.
The outboard carburetors idle mixture screws are plugged, the center carburetor isn’t.
The center carburetor is 350 cfm and the outboards are 500 cfm each.
The center carburetor opens by throttle linkage. The outboard carburetors open from engine vacuum.
The outboard carburetors have metering plates. The center carburetor has a metering block.
The center carburetor has jets. The outboard carburetors have fuel orifices.
The center carburetor has a power valve. The outboard carbs don’t.
The center carburetor has an accelerator pump. The outboards don’t.
The fuel site holes on the outboard fuel bowls are lower than the center carburetor’s site hole.
The center carburetor has the choke attached to it, the outboard carbs do not have a choke.

The next section does a deeper dive into each carburetor.

Center Carburetor

Let’s start with the middle carburetor. After all, it’s the one doing most of the heavy lifting even though it’s the smallest.

Here are some Six Pack center carburetor specifications:

Rated at 350 cfm.
1.50″ butterflies.
It has idle mixture screws.
Has an idle adjustment screw.
Has an accelerator pump.
Has a 6.5hg power valve.
It’s a center hung float.
Fuel inlet is on the passenger side.
Throttle linkage is on the driver’s side.
The choke mechanism is on the passenger side.
The vacuum lines are on the passenger side.
The fuel level sight screw is on the passenger side.

The engine uses the middle carburetor and the outboards to idle. The center carb is the only one with an idle adjustment screw which can be adjusted to lower or raise the idle.

The center carburetor has the choke mechanism located on the passenger side of the carburetor.

The throttle linkage attaches to the center carburetor only. The middle carburetor linkage doesn’t open the outboard carburetors, engine vacuum from the middle carb does.

The center carb base plate contains the vacuum attachments for the PCV and the choke. The main body has the vacuum attachment feeding the outboard carbs. The metering block has the vacuum attachment for the distributor.

Video detailing the Six Pack center carburetor, how it operates and typical problems.

Center Carburetor Factory Numbers

1969 Center automatic: 4392
1969 Center manual: 4391

1970 Center automatic: 4376
1970 Center manual: 4375

1971 Center automatic: 4670
1971 Center manual: 4669

1970 Center automatic: 4144 N95 (Cali. emissions)
1970 Center manual: 4374 N95 (Cali. emissions)

Learn about their dates codes in my article, 440 Six Pack Carb Numbers and Holley Date Codes.

Outboard Carburetors

The engine generates a lot of power, even just using the center carburetor alone. Although the fun really starts when the outboard carburetors are called into action.

If the forces pinning your body back into the seat wasn’t enough, the howl from the air rushing down the six barrels is an exhilarating experience.

It makes it difficult not to repeat the action of flooring the gas pedal to the floor. You can even see it in the video above how the driver chuckles and smiles after ripping through first and second gear over and over.

Here are the Six Pack outboard carburetor specifications:

Rated at 500 cfm each.
1.75″ butterflies.
No choke.
No idle adjustment screw.
Has idle mixture screws in the base plate which are plugged.
No accelerator pump.
Metering plate with gas passage orifice holes.
Contain a vacuum pod on the passenger side.
Center hung float.
Fuel inlet on the passenger side.
Butterfly linkage on the driver’s side.
Vacuum line on the passenger side.
The fuel level site screw is on the passenger side.

The outboard carb doesn’t have a metering block, it has a metering plate. They have fuel orifices allowing the fuel to pass through, there are no jets.

The front and rear carburetors have different metering plates.

The following is the outboard carbs metering plate numbers:

Rear carb: 35
Front carb: 34

The rear carb metering plate (#35) has two different size diameter fuel holes (staggered jetting). The passenger side hole has a .086 orifice hole and the driver’s side has a .093 orifice hole.

More than likely the engineers ran into an uneven intake runner or fuel feed issue and decided to use different size orifice holes.

The front carburetor metering plate (#34) has two .089 orifice holes.

The California emission carburetors have different plates and holes.

Each outboard carburetor has a linkage rod that connects together in the middle and attaches to the center carburetor linkage plate.

Video detailing how the Six Pack outboard carburetors operate and typical problems.

How does the outboard carburetors work?

Engine vacuum opens the outboard carburetors, not the throttle linkage. Although the middle carb linkage will limit the outer carbs from opening more if the middle carb is not fully open.

The vacuum from the center carburetor feeds the outboard carbs through vacuum lines. The vacuum feeds the vacuum pods on the outboard carbs which open the butterflies.

The outboard carbs also have a vacuum port in the body which assists with vacuum to the pod.

If the outboard carburetor has a bad vacuum diaphragm, the carb butterflies will not open.

When the gas pedal is released, the middle carb linkage plate closes the outer carbs linkage rods closing the butterflies. It’s shut down linkage. This can be seen in the video earlier or the video below.

Each outboard carburetor has a vacuum pod with a diaphragm and spring inside. They do not contain check balls.

The fuel bowl site hole is set slightly lower than the center carburetor’s site hole.

How throttle linkage operates on a Six Pack.

Six Pack Outboard Carburetor Numbers

1969 Front: 4393
1969 Rear: 4394

1970 Front: 4382
1970 Rear: 4383

1971 Front: 4671
1971 Rear: 4672

1970 Front 4175 N95 (Cali. emissions)
1970 Rear 4365 N95 (Cali. emissions)

Learn the best way to identify an original Six Pack Engine in my article, How to Identify a 440 Six Pack Engine.

Carburetor Tips

Tip 1

Many people will disconnect the outboard linkage rods when tuning and adjusting the center carburetor. When this is done, the vacuum line leading to the outboard carburetors should also be disconnected.

If the vacuum lines stay connected, if the center carb opens enough, engine vacuum will open the outboards also. Since the outboard carb linkage bars (shut down linkage) are disconnected, when the throttle is released, the center carb will close but the outboards will remain open and keep the engine revving.

It doesn’t take long for the engine to reach redline and it can lead to blowing the motor up.

Tip 2

The outboard carburetors have idle mixture screws in the front base of each carburetor. These are set at the factory, 3/4 of a turn out, and plugged.

Typically the factory adjustment is good and doesn’t have to be messed with. All three carburetors have an idle circuit.

Tip 3

Don’t over tighten the carburetor to manifold bolts. Over tightening combined with engine heat may lead to the base plate warping.

I have all the 440 Six Pack torque specifications in my article, 440 Six Pack or 6-BBL Specs, including the carburetor.

A warped base plate may bind the butterfly plate shaft preventing it from turning freely.

FAQs

How many carburetors does a 6 pack have? A 6 pack has three carburetors which are all two barrels each.

What does a six barrel mean? A Six Barrel refers to the carburetion system on a Plymouth 440 engine. A Six Barrel was produced from 1969-1971 and has three two barrel carburetors totaling 1,350 cfm.

Any questions or if you have more information you’d like to contribute, send us an email found on our contact page.