Muscle Mustangs & Fast Fords
1997 Ford 4.6L Two-Valve Engine Rebuild - Deuce On The Loose - Tech
Hopping Up A Two-Valve SOHC
With the recent introduction of the new 5.0L motor from Ford, it seems obvious that the Modular motor program is here to stay. Those diehard enthusiasts of the original 5.0L who are still waiting for Ford to come to its senses and bring back a modern version of the original pushrod motor need to come to grips with the reality that Elvis has indeed left the building. Though gone, the original 5.0L is not forgotten, and lives on in a great many buildups.
Another engine looking to follow in the footsteps is the original 4.6L Two-Valve motor. Not quite on par with the new or old 5.0L in terms of industry significance, there are (nonetheless) literally thousands of 4.6L Two-Valve motors around begging to be modified.
But do you stick with the all-motor, bolt-on route, step up to a stroker, or opt for forced induction? Heck, for that matter, why not combine a couple and toss in some nitrous for the ultimate in Two-Valve performance?
Fans of the all-motor route seek to optimize the flow, efficiency, and compatibility of their chosen components. Obviously, the forced-induction crowd relies on boost, while the nitrous contingent just adds a little squeeze. There are arguments for and against all three methods, as it takes one heck of an all-motor buildup to equal the power of a blower or turbo motor. That is where additional displacement via the stroker might come into play.
Since power output and cost are interrelated, building more NA power becomes quite expensive at some point given the output. Blowers and turbos offer impressive power potential, but problematic blower belts and turbo/intercooler fitment are issues that require attention. Plus, the well-designed turbo kits can drain your wallet. Of course, nitrous owners are labeled bottle-babies, but it's hard to argue wiht the power that is available at the push of a button. One thing for certain is that the debate will rage on as long as people have different opinions.
The reality is that there isn't one ideal avenue for performance. Even if we limit the desired power output to a nice round 400 hp, it doesn't take a genius to see that same 400 hp could be applied differently for different applications. Assuming the same peak power output, a heavy tow vehicle (especially a diesel) would require a decidedly different power curve than a hot street/strip Mustang. In addition to being application-specific, the power output can be component-specific as well, as there are many different combinations that can be assembled to reach the desired goal.
Plucked from a local wrecking yard, we began with a 197 Two-Valve, which means the early non-PI variety. Substantially weaker than the later 260hp PI version, the non-PI was the motor Ford offered to replace the original 5.0L. Unfortunately for Ford, the non-PI 4.6L lacked both torque and the high-rpm horsepower promised by the fancy overhead cam design.
Our test mule was a high-mileage unit, but a compression test revealed it still had plenty of performance left. After upgrading to Lucas synthetic oil, the motor was installed on the engine dyno and equipped with a Meziere electric water pump, Hooker long-tube headers, and a FAST engine management system. Using the FAST management system, the '97 GT motor was tuned to provide 266 hp at 5,000 rpm and 341 lb-ft of torque at 3,600 rpm. These non-Power Improved motors weren't rev happy, but they did manage to produce acceptable low-speed torque. Torque production from the 4.6L motor exceeded 300 lb-ft from 2,500 rpm to 4,600 rpm.
You may be wondering why an otherwise-stock '97 GT motor rated at just 215 hp produced over 260 hp on the engine dyno. The answer is quite easy, as the Ford rating of 215 hp came with a complete induction system; a full exhaust, including cats; and full accessories. The rating also includes running at operating temperature and using the factory tune (for air/fuel and timing).
For our "stock" test motor, we changed just about every parameter, including running a revised inlet system (open filter and section of 3-inch tube); a free-flowing exhaust, consisting of Hooker headers feeding 3-inch collector extensions; and absolutely no accessories (only an electric water pump). We also optimized the air/fuel and timing curves using the FAST management system (the factory tune was much more conservative) for performance, without concern for emissions.
Applying the basic bolt-on route, we replaced the factory power-producing components with more efficient aftermarket versions. Off came the stock '97 non-PI heads, cams, and intake manifold; on went CNC-ported heads from Total Engine Airflow (PN XE274H), Comp cams, and the late-model Power-Improved (PI) intake manifold. The late-model PI heads (ported by TEA) not only offer additional head flow (roughly 45 cfm per runner), they also increase the static compression thanks to smaller combustion chambers.
The combination of the additional compression, head (and intake) flow, and cam timing had a positive effect on the power output of our '97 GT test motor. Using the stock short-block with the TEA heads, Comp cams, and PI intake (and AccuFab TB and elbow), the 4.6L produced 390 hp at 5,900 rpm and 384 lb-ft of torque at 4,800 rpm.
Given the torquey nature of the stock non-PI motor, we expected the modified motor to sacrifice torque down low. After all, we did add much wilder cam timing. Lucky for us, the trade off in low-speed power was minimal. Credit the additional static compression for minimizing the low-speed losses. Torque production from the all-motor combination exceeded 350 lb-ft from 3,800 rpm to 5,800 rpm, making for one sweet powerband. In terms of idle quality, the XE274H cams were certainly lumpy, and if we had them available in time for testing, we'd opt for the (higher-lift) PI versions of the XE cams.
If you go looking to run this combination, the non-PI motor is actually a better starting point, as the PI short-block will offer lower compression when run with the PI heads. If you already own the PI motor and are changing the pistons or stepping up to a stroker, this is a moot point.