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Ford Engine Performance - Crower Cams - Taking Center Stage
Upping the power curve of a 4.6-liter P.I. engine with Crower 2V cams
Factory Cam profiles leave much to be desired in terms of performance, and for good reason. The stock cam profiles were not designed and ground with maximum performance in mind, and in fact, power output was but one of many other (probably more important) design criteria. When the factory designs a cam, it looks at many things, including cost of production, ease of installation, longevity (and associated warranty issues), effect on valvetrain and associated longevity and warranty issues, and engine/valvetrain noise, along with the all-important emissions, driveability, and overall performance issues.
Obviously, the engineers at Ford have the ability to design cam profiles for the modular motors that offer significant power gains compared to the current stock profiles-they just never get that opportunity. Luckily for us, the aftermarket has come to the rescue to provide all manner of cam profiles for the Ford modular motor program that prioritize performance. As it did with the 5.0, the aftermarket has embraced the modular motors, and now cam profiles are available for the Two-Valve, Three-Valve, and Four-Valve engine configurations.
For our test, we focused on the 4.6L Two-Valve GT motor circa 1999. Ford took steps to improve upon the original modular motors by offering the Power-Improved (P.I.) versions starting in 1999. The new-for-1999 P.I. motor featured improved breathing courtesy of revised cylinder heads and intake manifold. The new heads also allowed the use of high-lift (0.550 versus 0.500 for early non-P.I. motors) cam profiles that further increased the power output. The jump from the 225hp rating of the final non-P.I. motor in 1998 to the 260hp rating in 1999 seemed more than the numbers would indicate. Though nowhere near as impressive as the 300-plus-horsepower Four-Valve Cobra motors, the 260hp P.I. Mustangs could dip into the 13s in stock trim. While the stock P.I. motor offered a significant step up in performance compared to the '98-and-earlier non-P.I. combination, 260 hp just wasn't going to get it done against the LT-1 and LS-1 F-bodies of the world. Heaven forbid you should run up against a 300hp turbocharged import. Of course, you have to run 'em, but your buddies would never let you hear the end of it if a four-cylinder showed you nothing but taillights.
The 4.6L Two-Valve modular motors might not have registered too high on the specific output scale (less than 1 hp per cubic inch), and that was actually a blessing in disguise for perform-ance enthusiasts. The lack of power in stock trim meant there was plenty of extra power just wait-ing to be unleashed. In the case of the Two-Valve motor, some of that available power can be had by swappIng out the mild factory cam profiles. As we all know, there is power to be had from ported heads and a revised intake manifold, but so too is there additional power just waiting to be unleashed with more aggressive cam timing. It should be obvious from the factory power curves that the mild cam timing and long-runner intake combined to produce the engine's power peak at a rather relaxed engine speed. On our stock P.I. test motor, the peak power occurred at just 4,900 rpm. As we all know, producing more horsepower means shifting the torque curve. This means we can make more horsepower by producing the same torque value at a higher engine speed. Perhaps a brief example is in order here before we get to the test.
The mathematical relationship between horsepower and torque can be summarized by the following formula: HP = TQ x RPM/5252. What is evident from the formula is that horsepower can be increased either by increasing the torque value or the engine speed. Suppose we have a motor that produces 350 lb-ft of torque. If that 350 lb-ft occurs at 4,000 rpm, we have a horsepower rating of 266. If we increase the engine speed where the same 350 lb-ft occurs to 5,000 rpm, the power output increases to 333 hp. Shifting the engine speed even further to 6,000 rpm unearths 400 hp-all without increasing the torque production. In essence, this is what happens when you install wilder cam timing.
It is possible to increase the torque production with the proper cam profiles, but even if you simply increase the engine speed where the motor makes peak torque, you will be rewarded with an increase in horsepower. Of course, the possible downside to this shift is a loss in low-speed power. Such is the trade-off almost always inherent in a cam swap. This scenario is exactly what transpired when we replaced the factory P.I. cams with the wilder Stage 2 cams from Crower.
To test the effectiveness of the Crower Stage 2 cams, we first ran a mildly modified 4.6L Two-Valve P.I. motor supplied by Sean Hyland. Internally, the motor featured aforged reciprocating assembly but with stock compression. The forged short-block was topped with a set of stock (unported) P.I. heads and stock P.I. cams. To this combination we added a P51 intake and 75mm throttle body, a set of Kooks 151/48-inch headers, and a FAST engine-management system. The FAST system was used to dial in the air/fuel and timing curves of our test motor using the factory 19-pound injectors. Before being subjected to the rigors of the dyno, we filled the oil pan with five quarts of 5W-30 Lucas synthetic oil. Equipped with the stock P.I. cams, the mildly modified P.I. motor produced 297 hp at 4,900 rpm and 344 lb-ft of torque at 4,100 rpm. Torque production from the 4.6L Two-Valve motor exceeded 325 lb-ft of torque from 3,200 rpm to 4,800 rpm. Even down at 2,500 rpm, the little 281-inch motor exceeded 315 lb-ft of torque. As expected of the stock cams, torque production was adequate in the lower rev ranges, but the power fell off rapidly after 5,000 rpm.
This motor needed some extra breathing. The Crower Stage 2 cams offered a 0.559/0.570-inch lift split and a 224/228 duration split (at 0.050). According to Crower, the Stage 2 cams were designed for an effective operating range of 1,250 rpm to 6,000 rpm with an emphasis on midrange torque. Given the duration specs, we suspected the majority of the gains would come after the torque peak.
Once everything was buttoned up, we were ready for action. Some quick tuning with the FAST system and we were immediately rewarded with significant power gains. Crower cams recommended a valvespring upgrade with these cams, but our stock P.I. heads were already equipped with aftermarket valvesprings. Equipped with the Crower cams, the P.I. motor produced 345 hp and 351 lb-ft of torque. This represented a gain of nearly 50 hp over the stock cams measured peak to peak. The gains were actually even greater higher in the rev range (where the stock cams fell off rapidly). Torque production with the Crower cams exceeded 325 lb-ft from 3,400 rpm to 5,500 rpm-effectively shifting the torque curve (without a major change in the peak number)