The question on every enthusiast’s mind is a simple one: How do we make more power? In reality, the answer is quite simple, because there are many ways to improve the power output of any internal combustion engine, including the 4.6L modular Ford used for this dyno session. When you go looking to substantially improve power output, the first thing that comes to mind is forced induction. True enough, adding a turbo or supercharger to an otherwise stock motor will result in a significant power gain. The same can be said for a small dose of nitrous oxide. Adding a little juice to your motor can literally transform it from mundane to maniac, depending on the amount supplied. The final avenue is likely the most popular, often labeled the bolt-on or all-motor route. This involves replacing or otherwise improving the existing engine components to improve the breathing potential or efficiency of the engine. Things like ported heads, larger cams, and free-flowing exhaust systems fall into this category.
Naturally you can combine the all-motor improvements with forced induction and/or nitrous oxide for a more serious effort, but let’s take things one step at a time and add power by improving what we refer to as the “Big Three.” In terms of any performance engine, the “Big Three” refers to the top end of the motor, namely the heads, cam(s), and intake manifold. The reason for the “Big Three” label is that these major components all but dictate not only the power output of the motor, but the overall power curve. Of course, the short block must be up to snuff to accept the significant change in power, but the heads, cam, and intake will determine the efficiency of the motor. There are other components like the exhaust (specifically the header design) that can be employed to fine tune the power output, but the major players are still the heads, cam, and intake. Need proof of the power of the “Big Three?” Without changing any other components, we are able to increase the power output of a high-mileage 4.6L Ford by nearly 140 hp by replacing only the heads, cam(s), and intake manifold.
The test motor was a 4.6L two-valve Ford yanked from the engine bay of a ’97 Mustang. The modular motor was originally introduced back in 1991 in the Lincoln Town Car applications, though it wasn’t until 1996 that it replaced the venerable 5.0L (Windsor) in the Mustang, and in 1997 in the F-series trucks. The original 4.6L (and larger 5.4L) was hardly an immediate success, as the overhead cam design offered neither the high-rpm capability nor torque production to rival the original 5.0L. In 1991, the 4.6L was rated at just 190 hp, growing to 215 hp in the 1996 Mustang application, and 248 hp for the F-series in 1997. Things changed dramatically in 1999 when Ford introduced the so-called Power-Improved series of modular motors, which upped the ante to 260 hp in Mustang applications. Compared to the previous (Non-Power Improved) engines, the Power-Improved motors offered better-flowing heads, cam profiles, and a matching intake manifold. In essence, the Blue Oval boys improved the mod motor by changing the “Big Three.”
Ford’s mod motor has been further improved with the introduction of both three- and four-valve versions, but there are literally thousands of the original two-valve motors running around just begging for more power. To illustrate that it is possible to bring these early Non-PI motors up to (and beyond) PI output, and for that matter, both three and four-valve specs, we yanked a motor from the local wrecking yard and strapped it to the dyno. We then proceeded to replace the top-end components.
Don’t count out the 4.6L two-valve as a performance piece. Swapping the Big Three can add
The benefit of the introduction of the Power-Improved motors is that the early non-PI motors can be had for next to nothing. Choosing the Non-PI motor allowed us to demonstrate the power gains available to owners of both early and late two-valve F-series owners. In fact, the benefit of starting with the Non-PI motor is that adding a set of PI heads to a Non-PI short block will increase the static compression ratio over the factory Non-PI or even PI combinations. This increase comes from the fact that the later PI heads offer smaller combustion chambers (51 cc vs 42 ccc). Reducing the combustion chamber volume by 9 cc increased compression by nearly a full point.
All of our testing was run with the FAST management system. The FAST system allowed us to
The first order of business was to run the motor in stock configuration. The ’97 4.6L Ford was originally rated at 215 hp and 285 lb-ft of torque. Naturally this rating came with all accessories, full induction and exhaust systems, and running the factory timing and air/fuel curves. In essence, the power rating is the way the motor was run in the car. For our needs, the mod motor was equipped with no induction system other than the throttle body. No air filter, mass air meter, or associated induction plumbing was incorporated on the dyno. On the exhaust side, the single-cam motor was run with a set of 1-5/8-inch Hooker long-tube headers feeding 3-inch-diameter, 18-inch-long collector extensions without mufflers. The air/fuel and timing curves were optimized using a FAST XFI management system. This combination of the otherwise stock ’97 4.6L generated peak numbers of 268 hp at 5,100 rpm and 318 lb-ft of torque at 3,600 rpm. Despite the overhead cams, the Non-PI combination was not long on high-rpm power (peaking at just 5,100 rpm), but torque production from the 4.6L managed to exceed 300 lb-ft from 3,300 rpm to 4,600 rpm.