Muscle Mustangs & Fast Fords
Comp Cams Install - Project Redheaded Step Child Part 4
PI Power At Last
Things were about to get serious, as our '96 Mustang GT (a.k.a. Project Redheaded Step Child) was about to be treated to not only a set of performance cams, but also a set of long-tube headers and a cat-less X-pipe. You will remember that we subjected the 200,000-mile, non-PI motor to some minor mods in Part 1, then followed that up with some well-deserved maintenance items. After fresh oil, plugs, and wires, we were off to MagnaFlow to find some hidden horsepower (see "Project Redheaded Step Child, Part 3" in this issue).
The MagnaFlow exhaust mods included a new Tru-X pipe (which removed no fewer than four of the catalytic converters present on the factory cat pipe) and a new after-cat exhaust system. As expected, replacing the factory cat-pipe with the MagnaFlow Tru-X system significantly improved the exhaust flow. Though the after-cat exhaust offered less power gain than the X-pipe (as expected), the combination was worth as much as 15 hp.
When combined with the power gains offered by the minor mods in Part 1 (air intake, throttle body and plenum, custom chip, and underdrive pulleys), our lowly non-PI GT was finally starting to put down respectable power numbers. Unfortunately, and despite our best efforts, we still had not eclipsed the power output of a stock late-model PI 4.6. With '99-'04 GT power squarely in our sights, we decided to step up to not only a new set of cams, but also a set of long-tube headers.
We made our choices because it was high time we started seeing some serious power gains. Unfortunately, minor mods are not terribly beneficial on an otherwise stock 4.6, especially on this early non-PI version. The throttle body is a perfect example. While the larger 75mm Accufab throttle body we installed in Part 1 (with the C&L plenum) certainly outflowed the stock counterparts, the reality is that the stock components were not restricting airflow through the engine, at least not by much. Were we to test the larger throttle body and plenum on a wilder (higher horsepower) combination, the additional airflow supplied by the aftermarket components would certainly show larger power gains.
The components work well, but the stock (or even mildly modified) motor is not in a position (power-wise) to take advantage of the additional airflow. Knowing the minor mods offered commensurate power gains, we decided it was time to bring in the big guns-well, at least the medium-range guns, as the big guns will come once we install the ported heads (and larger cams) and a new intake manifold. Short of forced induction, we expect the ported heads and intake to offer the largest normally aspirated power gains. With the heads and intake yet to come, we proceeded with a new set of cams and a set of long-tube headers. First up were the new cams. Since the 4.6 was to see service as a daily driver, our cams were chosen accordingly. With driveability high on the list, we opted for the smallest Comp cams in the Xtreme Energy lineup. As with all the non-PI cams available from Comp Cams, the XE262H profiles offered 0.500 lift on both the intake and exhaust. The duration, however, was skewed in favor of the exhaust, with 224 degrees of intake duration to the 232 degrees of exhaust duration. The 114-degree lobe separation angle improved idle quality and helped produce a broad torque curve. We have employed the XE262H cams on both PI and non-PI motors in the past, with excellent results.
The cam profiles generally offer impressive power gains past 3,500 rpm with only minimal (if any) trade-off in low-speed power. True to form, the XE262H cams offered as much as 26 hp and 25 lb-ft of torque, with the peak-to-peak gains of 20 hp and 10 lb-ft of torque. Measured on the Super Flow chassis dyno, the XE262H cams upped the peak power from 210 hp at 4,400 rpm and 282 lb-ft of torque at 3,500 rpm to 230 hp at 4,700 rpm and 292 lb-ft at 3,500 rpm. The Comp Xtreme Energy cams improved the power output from 3,300 rpm to 5,700 rpm (and beyond, had we elected to run the motor any higher). Best of all, the additional midrange and top-end power came with no penalty in low-speed torque, as the 4.6 produced the same power from 1,500 rpm to 3,300 rpm with both cams.
Next up was the set of Hooker long-tube headers. The Hooker Super Comp headers featured 151/48-inch primary tubes and 3-inch collectors designed to maximize power from the 4.6-liter Two-Valve motor. Contrary to popular opinion, headers do not so much flow better than the stock exhaust manifolds as they do help improve the airflow through the motor by employing scavenging. This takes place by utilizing the kinetic energy of the outgoing gases to first produce a compression wave. True to the laws of physics, the trailing side of this compression wave features an expansion wave.
It is the expansion wave that reduces the pressure in the pipe (and exhaust port). This reduction in pressure helps draw air out of the cylinder and into the exhaust port. During overlap, this negative pressure also helps draw air into the cylinder through the recently opened intake valve. This scavenging effect is determined (for the most part) by the length of the primary tubes.
Excessively short tubes (such as those used on most stock exhaust manifolds) do not provide sufficient time for the compression wave to leave behind a depression capable of improving both the exhaust and intake flow (during overlap). The reduction in exhaust scavenging leaves behind stagnant gases that prevent the fresh intake charge from entering the combustion chamber.
From a labor standpoint, the long-tube headers required even more time to install than the cams. The headers themselves were quite easy to work with, but the 4.6 offered limited working space in the engine compartment. Unlike the conventional 302 pushrod engine, the 4.6 Two-Valve heads featured an overhang that limited both visibility and access to the mounting flange and retaining bolts.
While the instructions for the Two-Valve engine insisted it was possible to install headers with nothing more than unbolting the motor mounts and lifting the engine, the hot setup seems to be dropping the entire K-member. The success of sealing the header flanges depends on bolt access, which is almost nonexistent with the factory K-member in place. (Unfortunately, the author followed the instructions and left the K-member in place. Though none surfaced during the initial dyno testing, I expect leaks in the near future due to my inability to properly torque all the header flange bolts. Oh, how I miss performing header installations on the engine dyno. Thanks goes out to Steve from Powertrain Dynamics for use of the lift and tools, as I can't imagine performing the task in my driveway on my back.
While the install took every bit of a full day to perform the task (experienced Mustang mechanics can probably reduce the install time somewhat), the effort was rewarded with extra power. The Hooker long-tube headers and off-road X-pipe increased the power output of the 4.6-liter motor from 227 to 241 hp. You may notice the baseline number was down slightly from the runs made during the cam test. This was once again a difference between dynos as we performed the cam test on the Westech Super Flow chassis dyno and the header test on the Powertrain Dynamics Dynojet. This is why we make sure to reestablish a baseline before performing the component swap. The difference between the dynos was only a couple of horsepower (227.4 hp versus 229.8 hp), so we will credit the difference to dynos and/or test days.
Thanks to the improved scavenging, the headers improved the power output across the board, from 2,000 rpm all the way to 5,700 rpm. This non-PI motor did manage to cross an important milestone by eclipsing the 300 lb-ft mark with a new peak reading of 305 lb-ft at 3,500 rpm. I had hoped to reach the 250hp mark with the cams and headers, but the motor seemed to fall a little short. Fear not, as we will be back with ported non-PI heads and even larger cam profiles in the next issue.
Stock Non-PI cams vs. Comp XE262H
These are the kinds of power gains we like to see when we start swapping parts. Sure, the install took the better part of the afternoon, but the power offered by the Comp Xtreme Energy Cams was in line with the effort. So far, the cams added more power than any of the previous modifications to our redheaded step child. Tested on the Super Flow chassis dyno, the 4.6-liter put down 210 hp and 282 lb-ft of torque. After the installation of the Comp cams, the peak power jumped to 230 hp, while the torque peak inched closer to the magical 300 lb-ft number with a reading of 292 lb-ft.
Stock Exhaust Manifolds vs. Hooker Super Comp Headers
Actually, the test involved swapping out the stock exhaust manifolds and previously installed MagnaFlow X-pipe (with cats) in favor of the Hooker 151/48-inch Super Comp (long-tube) headers and new X-pipe (without cats). The new Hooker X-pipe was necessary to join the long-tube headers to the MagnaFlow after-cat exhaust. We also tested the Hooker after-cat exhaust, but the power difference between the two systems was minimal. Replacing the restrictive factory exhaust manifolds with the Hooker long-tube headers was worth as much as 15 hp and 18 lb-ft of torque. Note that the scavenging effect of the long-tube headers made itself known as low as 2,000 rpm while improving the power output from 2,000 rpm to 5,700 rpm.