Stock PI vs. XE262AH Cams...
Stock PI vs. XE262AH Cams
The mild XE262AH cams not only offered significantly more peak power (386 hp vs. 346 hp), but also more power throughout the tested rev range. The XE262AH cams increased the peak numbers by 40 hp and 20 lb-ft of torque, but the gains were as high as 55 hp at 6,500 rpm. As indicated, the best thing about the significant post-4,500 rpm power gains was that they came with no penalty in low-speed torque. The mild XE262AH cams increased the power output everywhere. When your cams gain power throughout the rev range, you know you've made a wise cam choice.
It's important to point out that these exceptional peak power gains come with a trade-off in low-speed and midrange power as well as a drop in both driveability and fuel mileage.
To illustrate the difference in power offered by both mild and wild cam profiles, we took a modified 4.6 Two-Valve motor and ran three sets of cams. The first set was obviously the stock PI cams, which were run to establish a baseline. After running the stock sticks, we installed a set of mild cams, followed by a set of wild ones. We chose from Comp Cams Xtreme Energy line, though other cam companies also offer comparable mild and wild cam grinds. The idea behind the test was to illustrate the gains in power offered by the mild and wild profiles in comparison to the stock PI profiles. It's important to note that our test motor was set up to accept and benefit from these aggressive cams. The 4.6 Two-Valve combination featured a reciprocating assembly from Coast High Performance, including a Cobra steel crank, forged rods, and pistons. The forged pistons not only had valve reliefs to provide sufficient piston-to-valve clearance for our wild XE278AH cams, but also a static compression ratio of 10.3:1 when combined with the PI cylinder heads.
Since we wanted to properly demonstrate the potential of the cam profiles, we decided to use something other than the stock PI heads. The additional flow offered by porting would allow the 4.6 motor to take full advantage of the wilder duration specs, not to mention the 0.550 lift. The stock PI heads were treated to full porting from Total Engine Airflow (TEA). The TEA treatment improved the intake airflow numbers from 177 cfm to 225 cfm, while the exhaust flow numbers jumped from 126 cfm to 208 cfm. Certainly not huge flow numbers compared to the current crop of 5.0 heads, but the Two-Valves performed well, and TEA offers a Stage 3 program that can up the flow rate to over 240 cfm. Working in conjunction with the TEA heads was a set of ARP head studs and Fel-Pro head gaskets. Also used on this Two-Valve test was a set of Hooker long-tube headers, a stock PI intake, and an Accufab 75mm throttle body and inlet elbow. The combination (especially the intake choice) is important as this will affect the so-called ideal cam choice. Given the head flow limitations (even our excellently ported heads from TEA) of the Two-Valve configuration, high-rpm power was never in the cards for this combination, so the cam profiles should be chosen accordingly.
Using the FAST management system, a pan full of Lucas synthetic oil, and a set of Denso iridium spark plugs, we ran the Two-Valve first with the stock PI cams. So equipped, the modified 4.6 Two-Valve motor produced 346 hp at 5,800 rpm and 363 lb-ft at 4,700 rpm. As you will see, it isn't a surprise that the combination responded so well to the cam swap. After all, the stock cams were the only component holding back the power output, since everything else had already been upgraded.
The first set of Comp cams to be installed was the XE262AHs, which offered 0.550 lift on both the intake and exhaust, and a 226/230 duration split (measured at 0.050). The cams were ground with a 113-degree lobe-separation angle. Equipped with the XE262AH cams, the peak power numbers jumped to 386 hp at 5,800 rpm and 383 lb-ft at 4,800 rpm. Note that despite a sizable jump in duration, the power peak still occurred at 5,800 rpm, while the torque peak shifted by just 100 rpm (from 4,700 rpm with the stock cams to 4,800 rpm with the Comp cams). This is a clear indication that the intake manifold was controlling the effective operating range of this motor. These mild Comp cams never lost power compared to the stock cams, and they bettered or equaled the power output from 3,000 rpm all the way to 6,500 rpm.
 Before installing the new...  Before installing the new Comp cams, we compressed each of the lifters in a vise to eliminate the preload and facilitate installation of the rocker arms. |  Comp Cams recommended new...  Comp Cams recommended new valvesprings when installing its cams, but our TEA heads already featured the beehive spring upgrade. |  Each XE262AH cam was installed...  Each XE262AH cam was installed with a liberal dose of cam lube. The XE262AH cams increased the power output of the 4.6 GT motor by 40 hp and 20 lb-ft of torque. The largest gain of 55 hp came at 6,500 rpm, but these mild cams never lost out to the stock cams in terms of power. |