Our test motor was a modified...
Our test motor was a modified 4.6L Two-Valve combination that represented what might be found under the hood of a mildly modified (normally aspirated) '96-'04 Mustang GT. Forged internals courtesy of Coast High Performance gave us a sound foundation.
Because of the dynamic nature of the equation, camshafts are one of the most misunderstood performance components on any motor. This is especially the case on the overhead-cam modular 4.6L Ford motor. The difficulty is only compounded when you add things like forced induction or nitrous oxide to the mix. From an anatomical standpoint, the camshaft can be likened to the brain, as the profile determines how effectively (when and where) breathing takes place.
Camshafts are one of the major determining components of the effective operating range of the motor, too. Of course, the cam timing must be combined with the proper intake manifold, head flow, and primary length on the exhaust for optimum operation over a given rpm range, but the right cam can almost determine the character or personality of the motor. Stock or ultra-mild aftermarket cams will provide a dead-smooth idle, while more radical grinds can transform that mild-mannered motor into one incredible ride. The radical-ride route usually includes ill-tempered, cantankerous behavior until the motor comes on the cam(s), but such is the price for all that high-rpm heaven.
The chore of improving the...
The chore of improving the head flow of the stock PI heads was given to the flow experts at Total Engine Airflow. They increased the flow rate of the PI heads significantly, allowing us to take full advantage of the larger cam profiles.
Many mod-motor enthusiasts at least understand the basics of cam timing. They realize that cam profiles come in a variety of different sizes. The high-lift and long-duration cams are much wilder and potentially more powerful than the wimpy production profiles. The problem arises when deciding to choose between these two extremes, especially for a daily driver.
The temptation is certainly there to go "big" on the cam profile. However, the cam profile must be selected not just for bragging rights on the Internet, but rather to work with your existing components. To be sure, adding the right cams to your otherwise stock motor can result in impressive power gains. Adding wild cams to your otherwise-stock motor may even result in a drop in power throughout most of the rev range, since the cams were designed to run effectively at 8,000 rpm and the rest of your stock components-intake runner length, head, and exhaust flow-sign off at just 6,500 rpm or less. This is especially true for Two-Valve modular motors. As a general rule, the closer to stock the remainder of the components, the milder the cam profiles that should be chosen. This means leave those weekend-warrior cams to the drag racers with lots of gear, aftermarket heads, and free-flowing exhaust. Instead, stick with mild, but effective, profiles that will offer power gains not just at high rpm, but throughout the desired rev range.
Topping off the modified GT...
Topping off the modified GT motor was a rather stock PI intake manifold. Though many aftermarket intakes are now available for the Two-Valve motor, we chose the PI intake. Look for a Two-Valve intake shootout in the near future.
While normally aspirated cam choices are difficult enough, pick up just about any book on the subject of forced induction and skip to the chapter on camshafts. Likely as not, the recommendation will be to run stock cams or at least to stay away from the dreaded duration or overlap that can cause precious boost to escape past the exhaust valves. While blowers (and turbos) work fine on stock motors equipped with stock cam profiles, they (just like their normally aspirated counterparts) respond well to more aggressive cam timing. In fact, for most street applications, the camshaft chosen for a mild, normally aspirated motor will work equally well with a supercharger. Sure, you can tailor the specific cam timing for supercharged use, but the gains will be minimal at most mild boost and power levels run on the street (compared to a normally aspirated performance cam).
This is good news for enthusiasts, as choosing the right cams for a blower motor is as easy as selecting them for a normally aspirated motor, and, in many cases, are actually the very same cams. In most cases, the cam manufacturers list their applications and many have included profiles for forced-induction motors. But the N/A cams work well, too. This means you can install performance cams in your normally aspirated Two-Valve combination and then save up for that supercharger without fear of having to swap the cams again.
 The PI intake was topped by...  The PI intake was topped by a 75mm throttle body and matching inlet elbow from Accufab. |  The exhaust system consisted...  The exhaust system consisted of a set of Hooker long-tube headers feeding 3-inch collector extensions. |  Tuning was provided by the...  Tuning was provided by the FAST XFI management system. All three combinations were run with the same ignition timing and air/fuel ratios to ensure accurate results. |