One of the things that made the new Hemi so successful was the impressive cylinder head flow. Even on the tuned-for-towing Ram applications, the 5.7L heads offered serious flow numbers. As-cast 5.7L heads flowed as much as 285 cfm, depending on the flow bench. To put these numbers into perspective, that is enough to support more than 570 hp on the right application. The flow numbers offered by the 6.1L SRT8 heads were even more impressive; the revised castings flowed 320 cfm, enough to support 640 hp on a serious buildup. These are flow numbers offered only by fully ported, aftermarket race versions of the LA or Magnum-style heads, and these came right from the factory. The most recent Eagle heads on the newer 5.7L Ram trucks flowed even more, with peak numbers eclipsing 330 cfm, good for an extra 20 hp (or more) more than the 6.1L heads. Of course, the Big-Kahuna Apache heads were offered on the latest 6.4L, and these flowed 340 cfm, enough to support almost 700 hp! Obviously, the Dodge engineers realized the importance of head flow when it comes to power production. They even left enough material on the as-cast heads to allow porting to further improve the flow.
The massive head flow offered by all of the stock Hemi heads is one of the major reasons why the Dodge engines respond so well to cam swaps. A performance cam is really the only thing missing in a performance Hemi combination, although it must be combined with the proper valve springs. If you check out chapter 2, you should realize that porting the stock heads is often of limited value. The reason is not the quality of the porting, but rather that the stock Hemi heads are already so good. The point here is that you shouldn’t expect huge power gains from a head swap, no matter what the flow bench says. If your modified 6.1L (or 6.4L) Hemi produces 580 hp with a set of (340 cfm) heads capable of supporting nearly 680 hp, don’t expect much of a change when you add heads with (380 cfm) flow numbers that support 760 hp. You don’t need better heads, you just need more engine!
In addition to camshafts and cylinder heads, this book contains separate chapters on nearly every aspect of Gen III Hemi performance, including intake manifolds, nitrous oxide, and even forced induction. With so much test data generated, I provided separate chapters on supercharging and turbocharging. Chapter 5 covers all of the various forms of supercharging, including Roots, twin-screw, and centrifugal superchargers. Chapter 6 covers both single and twin turbo testing. The different Hemi displacements all respond well to camshafts and they respond equally well to boost. Using boost from a super or turbocharger, it is possible to increase the power output of your Hemi by 50 to 100 percent or more. As illustrated by the test data in these two chapters, boost is simply a multiplier of the original output. Adding a turbo or supercharger to a stock engine will result in less of a power gain at any given boost level than adding the same boost to a modified engine. This book also covers the results of turbo and supercharged cam testing because the specs differ on cams designed specifically for forced induction.
One thing you will find out about the Gen III Hemis in this book is the relative lack of aftermarket support for things such as intake manifolds. Although the number of choices is limited compared to the offerings for the LS family, the stock Hemi intakes are already impressive performers. Testing has shown that it’s difficult to improve upon the factory Magnum and SRT8 intakes. It is often possible to increase power higher in the rev range (usually beyond 6,500 rpm) with a short-runner intake, but this usually comes with a trade-off in power lower in the rev range. The same can be said of producing power lower in the rev range, but this hurts power at high rpm. The tests on the adjustable intake manifolds (chapter 1) clearly illustrate this effect on the power curve. The comparison between the single-plane and long-runner electronic fuel injection (EFI) intakes show this as well; intake manifolds are designed to operate effectively at specific engine speeds. Short-runner (or single-plane carbureted) intakes should be combined with more aggressive cam timing designed to enhance power production higher in the rev range. Throttle bodies obviously work well with intake manifolds because they offer increased flow. The gains offered by throttle body upgrades increase with the power output of the engine. Tested on a stock engine, a throttle body upgrade might be worth nothing, but tested on an 800-hp supercharged combination, it can be worth as much as 50–60 hp (especially on a positive displacement supercharged application).
Chapters 7 and 8 include nitrous oxide, dedicated engine builds, and what I call overflow, meaning some of the tests that I ran out of room for. Nitrous oxide can be applied to any Hemi combination, ranging from a stock crate engine to a dedicated stroker (including turbo and supercharged combos). The amount of power supplied by nitrous oxide is a function of the jetting; larger jets allow more nitrous flow. Of course, this must be accompanied by the proper amount of fuel, but nitrous systems offer far and away the most bang for the buck. It is possible to add as much as 250 hp (or more) to your Hemi for about the cost of a cam swap. You will make more power with nitrous and a cam, but every Hemi owner should experience nitrous oxide once in his or her life.
I have broken down the chapters into individual components (for example, heads, cams, and intakes), but the reality is that the best way to produce optimum power from your Hemi combination is with the proper combination of components. The heads must work with the cam timing and intake design to optimize power production in the same RPM range. If you want to know how to make your Hemi more powerful with dyno-verified results, you’ll find it in these pages.
Whether you have a stock, street, or strip Hemi application, the intake manifold is one of the three major players in terms of power production. Unlike the LS, the aftermarket has not stepped up with an abundance of aftermarket Hemi intakes, although we did manage to test just about everything available. Contrary to popular belief, intake designs do more than just allow airflow into the ports, they actually provide a tuning effect that aides in power production over a given RPM range. Not surprisingly, factory Hemi intake manifolds for the truck, Magnum, and SRT versions were not designed with peak power production in mind, but rather a combination of peak and average power combined with ease of production and even fuel mileage. Just as a poorly designed manifold can (literally) ruin an otherwise good Hemi, the right intake can help you produce impressive power, especially when used in conjunction with the right cam and ported cylinder heads. More than any other single component, the intake manifold’s runner length will determine where the engine makes effective power. Match the runner length to produce power in the same operating range as the cam profile, and you are a long way toward making a powerful Hemi.
All of the factory Mopar intakes perform very well, including the aluminum SRT8 manifold.
For 5.7L, 6.1L, and 6.4L Hemis and any other engine, intake manifold design may be broken down into three major elements, runner length cross section as well as taper ratio and plenum volume. These elements are listed in order of importance or, more specifically, in the order they most affect the performance of a given manifold. By this we mean that changing the runner length has somewhat more of an effect than altering the cross section or plenum volume. This is not to say that all of the elements are not important, it is just that proper care should be given to the elements in accordance with their eventual effect on performance. Intake designers, take note of this perspective, because fabricators often spend countless hours altering the plenum volume in an attempt to change the effective operating range when they should have simply increased (or decreased) the runner length. It should be stated here that manifold design is sometimes limited by production capability or rather ease of construction. Building a set of runners with a dedicated taper ratio and a compound curve is difficult if not impossible for the average fabricator. Despite the fact that this design produces the best power, it simply