Guide
ACKNOWLEDGMENTS
This rebuild book is my second Gen III Hemi engine book, and I am still learning things about this engine. The Chrysler/Mopar Generation III Hemi V-8 engine has been in production for more than 15 years, which is about twice as long as its predecessors Gen I (7 years) and Gen II (7 years). There were thousands of the first two Hemis built, and now Chrysler has built more than 3.7 million of the Gen III engines. The Gen III engines went into production after I retired, so I had a lot of catching up to do to write this book as well as New Hemi Engines 2003–Present: How to Build Max Performance. Helping with my education was Rob Cunningham of Mancini Racing.
With any new engine family, special and high-performance parts can be an issue, so hats off to Modern Muscle (aluminum intakes, adapters, and custom porting), Indy Heads (aluminum intakes and porting), Edelbrock (aluminum heads and intakes), and Prefix (aluminum block, porting, and ECM refresh) for maintaining and expanding the key performance parts for the Gen III Hemi. Many thanks to all the parts suppliers of cranks, rods, pistons, cams, valvetrains, oil pans, headers/exhausts, and gaskets that have supplied the upgrades to work with the various block and head combinations. Additionally, I must not forget all the turners, reprogrammers, and computer companies that worked with the new parts to make them compatible with the computers along with stand-alone hardware, turning great performance potential into higher and higher horsepower outputs. I want to thank the many manufacturers that display their new Gen III hardware at events and shows such as the Mopar Nats, Chryslers at Carlisle, PRI, and SEMA, as well as their representatives, who are always willing to answer questions and discuss the latest hardware.
The writing and photography required for an engine book is a lot of work but not anywhere near the amount of work that went into the design and development of the parts originally. Many thanks to Bob Lee and the Chrysler designers for a job well done, plus extra thanks for the early work by Tom Hoover and John Wehrly. Engine programs have many steps, phases, and milestones, and I would like to thank several behind-the-scenes Hemi heroes including Pat Baer, Bill Hancock, Tim Zuehlke, Jim Szilagyi, Al Nichols, Dale Aldo (Drag Pak vehicles), and Gary Stanton (Stanton Racing Engines). There are too many racers who have helped and are helping with the engine development efforts to name individually, but thanks to all!
Many extra thanks to Joe Kummer, Chrysler engineer, for his behind-the-scenes help and his research with service manuals and specifications. I would like to thank Bob McSwain (Godfather Racing), for his very valuable help and assistance. Additionally, I would like to thank Bob Kobylski (Modern Cylinder Head), for his patience and helpful assistance. Many, many thanks to Dale Matthews (Prefix) and his team of engine builders—I couldn’t have done it without them! They all put in lots of time to help me put photos and words to my books.
I owe the most thanks of all to Dave Weber (Modern Muscle) and his team at Modern Muscle Xtreme, especially Rob Busey, Byron Walker, and Christian Evens, for not only helping me with this book but for showing the way with a new engine program, parts, and development and having a willingness to share this information with us all.
Perhaps most of all, I must thank my editors Paul Johnson and Bob Wilson at CarTech for their patience, foresight, and guidance as we took my manuscript and photos and created a readable book.
I would like to give extra special thanks to my wife, Linda, for her patience and assistance during this project.
DEDICATION
I would like to dedicate this book to all of the Chrysler engineers, designers, and mechanics who designed, developed, and tested this engine, and to all of the UAW assembly line workers who put them together and installed them into cars, trucks, and SUVs on a regular basis and have been doing so for more than 14 years and more than 3.5 million units. I also dedicate this book to all of the mechanics who have maintained these engines at dealerships and shops across the country, as well as the engine builders, chassis builders, and racers who took a chance on a brand-new engine design and followed up by supporting the Drag Pak program, which uses this Gen III Hemi engine in many variations. Thanks to all!
INTRODUCTION
What is a Hemi? The short answer is that Hemi is short for hemispherical, which relates to the engine’s combustion chamber shape. There are several ways to group engines: size (cubic inches or liters), number of cylinders and alignment (inline-6 or V-8), and valve arrangement (flathead, wedge, or opposed).
When looking at valve arrangement, flatheads have the valves in the block. With a wedge, the valves are overhead and sit next to each other along the cam centerline. For the opposed valves arrangement, the two valves (intake and exhaust) are on opposite sides of the chamber, resulting in a chamber that looks like a hemisphere. This opposed valve layout and the typical valve angles it used became known as the Hemi.
Engine Development
In the early and mid-1950s, the Gen I engines produced the 331, 354, and 392. From 1964 to 1971, the well-known Gen II engines produced the 426. While the Gen III Hemi was an all-new engine design introduced in 2003, it takes features from both of its ancestors and adds many unique features.
The Gen III Hemi engines in production today have evolved from a long line of performance/race Hemi engines that also did double duty as production engines. These new Hemi engines shared many features with the Chrysler/Mopar small-block engines.
During the past 14 years, Chrysler engineers and mechanics have done a tremendous amount of engine development. There’s been so much testing that Chrysler has had anywhere from 10 to 100 engines running on dynos and in cars for 8 to 16 hours per day, 7 days a week, for 14 years! One of the results of this testing and development was the 2009 Eagle 5.7L engine, which increased from 345 hp to about 390 hp. Another result introduced in 2011 was the 392-ci Apache engine, which produces 485 hp in full emissions and warranty trim.
From all of their testing data and technical information, Chrysler engineers and designers took what they felt would make the best production engine for the new millennium and added special high-tech hardware, such as the multi-displacement system (MDS), variable valve timing (VVT), and the active intake manifold. These unique features and the advanced technology that go with them are just beginning to be explored by engine builders and manufacturers looking to make race cars and special performance vehicles be more competitive.
The Gen II Hemi engines use a wide, deep, or thick valve cover with one single plug in the center of the cover for each cylinder. The plug wire uses a large round seal on top of the cover, which highlights the plug location. There was a twin-plug version of the Gen II, but they are very rare. (Photo courtesy Bob Wilson)
The easiest way to identify a Hemi engine is to look at the valve cover. The Gen III Hemi engines use a fairly shallow plastic valve cover with two holes for each cylinder because all Gen III Hemi engines use dual plugs.
Engine tuning used to be set the distributor (ignition timing) and adjust or jet the carburetor. This basic approach all changed with the introduction of multi-point injection (MPI) and the engine computer. The MPI computer controls everything, including fuel and ignition, so every application and modification requires that the computer be reprogrammed or reflashed. In the mid to late 1990s and early 2000s, Chrysler developed the engine control module (ECM) for reprogramming. The carmaker sold ECMs directly to customers. This led to aftermarket performance code breakers offering the
