Regular price $979.00

Add 2003-2004 APPS Bracket?
Intercooler Outlet Size
Intake Horn Color

See application notes before ordering!


'03-'07 Dodge Ram 5.9L Cummins Mega-Rail Installation Kit

Now there's a way to fuel and cool that fire breathing 5.9L your building. Massive airflow increases along with the rail capacity and flow to feed even the largest injectors makes the Mega Rail kit unbeatable!

The Mega-Rail Installation Kit includes the GDP Mega-Flo Intake Manifold, Air-Boss 67 and needed parts for installation of the entire fuel rail system from the larger 6.7L applications onto the 5.9L Cummins. This simple bolt on package gives the 5.9L Cummins an edge in airflow and fueling like never before. Finally you can get the most from your modified injection pump and performance injectors! With the abundance of used 6.7 parts the Mega-Rail Installation Kit is perfect for customers who choose to supply their own 6.7L rail system and crossover tubes.

Using our Mega-Flo intake manifold, Air-Boss 67 plenum and factory Bosch HPCR parts we have created a package that is reliable, easy to install, and out flows any other parts combination on the market. If you're pushing the envelope on 5.9L Cummins performance the Mega-Rail kit can fuel it.

Benefits of the Mega-Rail Conversion:

• 50% increase in fuel rail capacity – Perfect for modified CP-3’s

• 50% increase in injector line size – Handles even the largest injectors

• 3000 psi higher rail relief valve pressure – No need for rail plugs, we leave the safety in the system

• 110% increase plenum entrance area – Over double the air entrance area at the plenum

• 20% larger intercooler piping - 3.50” Intercooler piping and intake manifold vs. 3.00” stock

• 100% Bolt-on installation!

The GDP Mega-Rail Installation Kit is an installation kit only and does NOT include the 6.7L rail, lines, or crossover tubes. For those customers who would like to purchase all of the needed items in one package we offer the Mega-Rail System which includes the 6.7L fuel rail, injector lines, and crossover tubes in a complete package.

Mega-Rail Installation Kit Includes:

Mega-Flo Intake Manifold
Air-Boss 67 Billet Plenum
3.50" Intercooler Pipe & Boots
High Pressure Return Line System
Rail Pressure Sensor Extension Harness
Dipstick Bracket
All Required Hardware & Gaskets

Note 1: This conversion kit eliminates the factory grid heater but we do offer a grid heater option.

Note 2: ONLY compatible with single CP-3, Fleece or ATS 6.7L twin CP-3 kits.

Note 3: If you intend to run this kit with twin CP-3's you MUST use an ATS or Fleece kit intended for the 6.7L applications. This kit will not fit trucks equipped with a twin pump kit intended for use on a 5.9L application.

Note 4: The intake manifold in this kit has been machined for 5.9L Cummins applications only. It will not work on the newer 6.7L engine.

Mega-Rail tips, tricks and myths

Thru the course of installing the Mega-rail System we have come across a few things that you may find useful.

First is the rail pressure sensor. With minor electrical connector modification the stock 6.7L rail pressure sensor can be used on the 5.9L trucks. Due to voltage mapping differences the stock 5.9L rail pressure sensor reads roughly 13% higher than the stock 6.7L sensor at the same voltage. This can be used to your advantage if you are careful.

By using the 6.7 pressure sensor on the 5.9 you can raise rail pressure approximately 13% without using a pressure box. For example, at WOT this equates to 24,860 psi actual at an ECM reported 22,000 psi. At idle reported pressure would be 5000 psi with actual being 5,650 so the difference is very small. At a reported cruise pressure of 8000 psi the actual would be 9,040 psi and this small increase is good for mileage. Since rail pressure is in essence "fooled" you will need a 6.7L rail pressure gauge connected directly to the sensor to see actual rail pressure readings.

Now, for the warnings and disclaimers...

Use the 6.7L rail pressure sensor at your own risk! Do not use the 6.7L rail pressure sensor if you are running a pressure box! If your tuner of choice has a rail pressure adjustment setting we recommend running the tuner at the "stock" pressure setting. Most tuners increase rail pressure to some degree. When combined with the 6.7L sensor rail pressures can get out of hand quickly. When using the 6.7L sensor always monitor actual rail pressure with a standalone 6.7L rail pressure gauge such as the unit offered by ISSPRO.

Next up is the grid heater. There has been some talk of using the stock 6.7L grid heaters (with the Mega-Rail kit) on the 5.9L head. The stock 6.7L grid heater will NOT fit the plenum opening of the 5.9L head without modification to a small casting area under the plenum cover. It can be made to work but minor grinding will be required.

We always recommend using new parts when working on the HPCR fuel systems. However, if you are looking to save some money, there are many sources for used 6.7L rails and injector lines. Wrecking yards and core supply shops have good inventory levels of used 6.7L parts now and can save you some money over buying a brand new rail and lines. Using a Mega-Rail Installation kit and a used rail setup is a great way to make big power on a budget.


Black Diamond Diesel Performance & Fabrication is a locally owned and operated shop specializing in high performance diesel and custom fabrication. From maintenance/repair to street/strip we are your one-stop shop! Building the Southwest's fastest diesel trucks, stop by our shop and see how we can improve your vehicles performance and reliability!