Mopar 340 Six Pack

Tri-Power, 3 dueces, Six Pack - they all refer to the idea of having three 2 barrel carburetors feeding the appetite of a hungry big block. They were popularized in the mid 1960's by Pontiac's GTO, but were also used on other GM engines as well as Ford. Mopar didn't get in the game until 1969, but the wait was worth it.

The earlier tri-power systems used by GM and Ford used a mechanical linkage to open the end carbs. This worked great on cars with manual transmissions, especially on the drag strip. On the street, though (especially with an automatic transmission), stabbing the gas pedal too quickly could result in a colossal bog as the end carbs tried to dump in too much air and fuel before the engine was ready for it.

Chrysler used a different method to open the end carburetors. Instead of using a mechanical linkage, the Mopar Six Pack used engine vacuum. This ensures the end carbs will never open until the engine is ready for the extra air and fuel. Because of this change, the Mopar Six Pack worked extremely well on the street, giving outstanding performance even in cars equipped with automatic transmissions.

Can you really build a car that will give you great performance and decent fuel economy? With Mopar's 340 Six Pack, the answer is yes.

Usually when choosing an intake system, you have to decide whether you want performance or economy. If your goal is good fuel economy, you select a small carburetor and adjust it for a lean air-fuel mixture. While this can give great fuel economy, such a setup will limit your performance. If you want to make good power, you do the opposite: select a large carburetor and adjust it for a rich air-fuel mixture. This route can give outstanding power, but your gas mileage will be crappy at best.

With a Six Pack, you get the best of both worlds. While driving at low throttle settings, you are only using the center carburetor. This carb is only rated at 350 cfm, which is smaller than even the puniest "performance" carburetor. You can also adjust it lean, since you're only using it in low power situations. When you need power, the end carbs open up. These are rated at 500 cfm each, giving a total airflow capacity of 1350 cfm - badder than all but the biggest Holley Dominator racing carb - but only when you need it.

Unless you have an AAR Cuda or Challenger TA, you probably don't have a factory 340 Six Pack. Fortunately, you can build your own using all newly manufactured parts. The Mopar Six-Pack Engine Handbook, written by Mopar engine guru Larry Shepard and available from Amazon tells you everything you need to know in order to build your own Mopar Six Pack engine. This is an excellent book. Besides telling you how to set up your own Mopar engine for a Six Pack induction system (the book covers both small block and big block engines, including the Magnum small blocks), sections are included on Six Pack history, theory, design, and tuning. There are also sections included on engine and chasis modifications that will work to ensure you're getting the most out of your Six Pack equipped engine. If you are planning to build or modify your own Six Pack engine, or are just curious, I highly recommend this book.

Factory Fresh Six Pack

As it came by the factory, the Mopar Six Pack setup is one of the best induction systems (carbureted, anyway) ever put on a production vehicle. If you're working on a restoration or just like the OEM look, the stock Six Pack system will run just fine. If you have a modified engine though, or would like to increase the tunability and reliability of your Six Pack engine there are 3 areas that can be addressed.

Six Pack Braided Fuel Line

The stock upper fuel line on a Six Pack is actually composed of 4 separate pieces of steel tubing connected with 2 brass blocks. The tubing is rigid, and over time vibration can cause the connections to come lose and leak, or worse, crack. The solution is simple: replace the stock fuel tubing setup with a braided steel fuel line kit from Promax Carbs. They actually offer 2 kits. The upper kit replaces the fuel feed to the carburetor. Besides offering greater reliability than the stock upper fuel line setup, Promax's kit also includes a fuel pressure meter. The only down side is that it definitely looks after market. The second kit they offer is the lower line kit, which runs from the fuel pump to the upper lines. This kit includes a fuel filter. While not as critical as the upper fuel line kit, this kit matches the appearance of the upper kit and your engine will look a lot better if you run both.

Billet Jet Plates

The stock Six Pack end carburetors use metering plates, similar to the secondary side on 4160 series carbs. While this works well for stock applications, it can make it a pain to tune a modified engine. The only way tot une is to buy new metering plates or drill your existing plates. New plates are expensive and the metering holes are the same size for both sides of the carb

Billet Throttle Base

Billet throttle plates from... allow you to adjust the idle mixture on the rear carburetor.

As it came by the factory, the Mopar Six Pack setup is one of the best induction systems (carbureted, anyway) ever put on a production vehicle. That doesn't mean there is no room for improvement though.

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