New Hemi Engines 2003-Present. Larry Shepard

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 same reprogramming service. Today, the aftermarket offers handheld units that work with the production ECM and can control almost every engine function for all applications.

       All Gen III Hemi production engines use multi-point injection (MPI). The MPI system uses one injection in the intake manifold port runner at the manifold face (just above the valve cover). The injectors are fed fuel from the fuel rail, which is the long tube parallel to the cam centerline that sits above the four injectors. The throttle body mounts on top of the manifold or at the front, depending upon application.

       All Gen III Hemi production engines come with MPI. However, a carburetor and distributor are desired for some applications, such as hot rods, street machines, and custom builds. Prefix makes a new front cover kit for these engines that allows the use of a distributor (blue cap in upper left) and a mechanical fuel pump (used with a carburetor) mounted at the lower middle.

       Horsepower Production

      In the mid-1950s, the Gen I Hemi engine made almost 1 horsepower per cubic inch (hp/ci), and in 1958 its big brother the 392 was only a few horsepower short of the magic 1 hp/ci goal. The Gen II 426 Hemi was only 1 hp short of that 1 hp/ci goal in its production period through 1971. For comparison, the original Gen III 5.7L Hemi has 345 ci and was rated at 345 hp in 2003. While this isn’t a fair comparison, it illustrates that the new Gen III Hemi fits in well with the family tradition.

      In the 1960s, there were only three companies that rated engines: General Motors, Ford, and Chrysler. Production engines were rated on a cold bare gross system (basically open exhaust and no accessories) and a net system, and the advertised ratings were somewhere in between. Before 1972, guidelines were just that, so any rating came with many unknowns. In an effort to improve this situation for consumers, the federal government asked the Society of Automobile Engineers (SAE) to define this engine rating system based on the new emissions regulations in 1972. The advertised rating moved closer to the net rating and the gross or cold bare gross rating went away. The switch in systems caused a big drop in the horsepower ratings for almost all engines. However, the compression ratio drop hurt the high-performance engines more because they dropped from 10.5 to 8.5 while other regular-performance engines went from 8.5 to 8.0.

      Since then, government regulations have adjusted the ratings definition to more closely match the vehicle. With the new system, there is no flexibility. Government officials have been trying to get to an as-installed number, as most agree that using net ratings is misleading. Today, the system is still watched closely. There haven’t been any major revisions during the 14 years of Gen III Hemi production. This means that the rating given for your engine will be close to what you will get from the assembly when you rebuild it.

       Production engines are rated in the 345-hp to 485/490-hp range with the supercharged 707-hp and 840-hp versions covering the big end. Each engine has a cover that spells out the engine or identifies it as supercharged. The covers sit on two round plugs on top of the valve covers. There are large single covers,