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.
After running the stock Non-PI motor on the dyno, we pulled the heads, cams, and intake ma
Part One: More Flow, More Compression
1. Now it was time to swap the top, meaning replacing the heads, cams, and intake manifold. Starting with the cylinder heads, the Non-PI heads were replaced not just with a set of later-model PI heads, but PI heads that had been treated to the Stage 2 porting process by Total Engine Airflow. Until Trick Flow Specialties introduces the first aftermarket two-valve head, the only route to improving the factory heads is with porting. The guys at Total Engine Airflow improved the flow rate of the factory PI casting from 177 cfm to 226 cfm on the intake side and 126 cfm to 209 cfm on the exhaust side. This represented flow improvements of nearly 28% on the intake and a whopping 65% on the exhaust. These flow rates were combined with the jump in static compression from 9.3:1 to nearly 10.3:1. This increase in compression not only improves power, but also throttle response and fuel mileage. The compression hike is still well within the range of safe use on pump gas, especially when you combine it with the slightly wilder cam timing offered by the Xtreme energy series we installed.
This shot illustrates the difference between the PI and Non-PI heads. Both the ports and w
Not content to simply install stock PI heads, we sent ours off to Total Engine Airflow for
Another significant difference between the PI and Non-PI heads was the combustion chamber
Though not strictly a performance upgrade, we replaced the stock valve covers with these a
Part Two: Bigger Bumpsticks
2. Step two of our big three was to replace the factory Non-PI cams with performance grinds. The Non-PI cams differed from their later PI version by way of lift. Where the Non-PI cam offered less than .500 lift, the PI versions stepped up the lift to .535. The lift increase only makes the PI better than the Non-PI, but we were obviously looking for a great deal more power than the mild duration figures offered by either. Leafing through the Comp Cams catalog revealed a set of XE270AH cams that offered not only .550 lift (both intake and exhaust), but a 234/238 duration split. These represented a sizable jump over either of the factory cams profiles, especially considering that our newly ported heads flowed exceptionally well right up to .600 lift. The final performance mod was to replace the factory Non-PI intake with a PI version. Not only was this a performance upgrade, but it was a requirement as the Non-PI intake ports and water passages do not line up with those in the PI head. The PI intake was combined with an inlet elbow and 75mm throttle body from Accufab.
The Non-PI cams offered both low lift and mild duration figures. The later PI cams increas
In the end, we went with a set of performance cams from Comp Cams. The XE270AH cams offere
Part Three: Better Intake Manifolds
3. While you might expect the slightly wilder cam timing to trade low-speed power compared to the stock combination, our top-end mods improved power everywhere, from 3,000 rpm all the way through 6,200 rpm. Had we elected to tug the new combo down to 2,500 rpm during the test, it would have been better there as well. The peak numbers improved dramatically, from 268 hp and 318 lb-ft to 405 hp and 393 lb-ft. The engine speeds for these peak numbers rose as well. Where the previous combination produced peak power at just 5,100 rpm and peak torque at 3,600 rpm, the new combo produced peak power at 6,000 rpm and peak torque at 4,900 rpm. Measured peak to peak, the power improved by 137 hp and 75 lb-ft, but elsewhere along the curve the gains exceeded 150 hp and 130 lb-ft of torque.
Use of the PI heads required a matching PI intake manifold. The PI intake was topped with
Changing the big three resulted in significant power gains. The modifications increased th
Rather than running the PI intake from the Mustang, it is possible to top the 4.6L with th
It should be noted that it is possible to further enhance low-speed (below 4,000 rpm) torque by replacing the composite Mustang PI intake with the aluminum truck version. This will improve the torque production by 15-20 lb-ft below 4,000 rpm, but the tradeoff will be a loss in power from 4,000 rpm to 6,000 rpm (25-30 hp). If sub-4,000 rpm is most important for your application, you would be best served by dropping down in cam profile to the XE262AH profiles to better match the truck intake. The trick divided plenum in the truck intake greatly improves power between 2,500 rpm and 3,000 rpm using Helmholtz resonance tuning, something not available in the Mustang version. Of course you are now free to toss in a stroker short block under the combo or add nitrous or forced induction, but that is a test for another day.
2. The truck intake also features a unique divided plenum. The plenum volume has a definit
3. A servo-activated divider is used to separate or join the plenum volumes. This activati
1. The difference in height between the truck and PI intake is visible in this photo. The
4. Use of the truck intake will improve power production up to 4,000 rpm. Unfortunately, t
The Final Word
The dyno results reveal that there is plenty of power to be had even with nothing more exotic than a stock, high-mileage short block. Topping the stock non-PI short block with ported PI heads, a set of aggressive but streetable Comp Xtreme Energy cams, and a PI intake manifold, improved power production by as much as 140 hp. Obviously it would be better to start this buildup with a fresh short block, but if money is tight (isn’t it always?), then adding the right top-end package to your 4.6L or 5.4L mod motor can offer huge dividends.
Stock Vs Big Three ’98 4.6L 2V Ford
It is immediately obvious from the power curves offered by the stock ’98 4.6L two-valve motor that Ford was not concerned much about high-rpm power. Run with no accessories, long-tube headers and a FAST XFI management system, the wrecking yard wonder produced just 268 hp, though a fairly impressive 322 lb-ft of torque. Credit the long-runner intake, small intake ports and mild cam timing of the early non-PI motor for its torque nature. Replacing the big three performance components (heads, cams and intake) resulted in a sizable jump in power. Adding the ported PI heads (which also increased the static compression), the wilder (but still streetable) Xtreme Energy cams and matching PI intake manifold improved the peak power numbers to 405 hp and 393 lb-ft of torque. Despite the more aggressive cam timing, the top-end package improved the power output from as low as 3,000 rpm (even lower had we lugged the new combo down at 2,500 rpm) out past 6,000 rpm. This is a combination that will start by feeling pretty good when you put your foot down and then proceed to feel really good as the engine speed increases.