July 1, 2008

Running a Meziere electric water pump allowed us to eliminate the usual array of accessories. Naturally, this had a positive effect on power production, but the engine enjoyed the benefits of running without accessories and factory induction in stock and modified trim. The final modification was to install a set of Hooker long-tube headers. Actually, the headers were used in stock trim as well, as this simplified exhaust routing on the dyno. All we had to do after installing the stock '97 motor on the dyno was establish a baseline, install the performance upgrades, and run it one final time.

After filling the crankcase with 5W-30 Lucas synthetic oil and careful tuning of the '97 Two-Valve motor, we were rewarded with baseline numbers of 258 hp at 4,800 rpm and 341 lb-ft of torque at 3,500 rpm. The combination of long intake runners, small head ports, and mild cam timing produced relatively impressive low-speed torque production, with the 281ci motor producing more than 300 lb-ft of torque from 2,500 rpm to 4,500 rpm. Unfortunately, this combination greatly limited power production at the top of the rev range. Once the power curve reached 4,000 rpm, it leveled off until 5,200 rpm. The result was a flat power curve for a solid 1,200-rpm spread. It should be noted that the difference between the rated power output of 215 hp and the numbers produced on the dyno can be attributed to the lack of accessories, a low-restriction induction, an open-exhaust system, and the maximized performance tune provided by the FAST system. We also ran this motor with long-tube headers at a water temperature of 150 degrees, where the rated power output comes at normal operating temperature. Regardless of the power numbers generated by the dyno, we were looking for a difference from our performance modifications.

After backup runs repeated the baseline power numbers, the stock heads, intake, and camshafts came off. They were replaced by the TEA-ported PI heads, a matching intake manifold, and Xtreme Energy cams. The Accufab 75mm throttle body, Hooker long-tube headers, and 19-pound injectors were retained from the previous test, though we increased the static fuel pressure by nearly 20 psi for this test. To properly secure the new TEA heads, we elected to replace the factory head gaskets with MLS gaskets from Fel-Pro. They were clamped in place using a set of ARP head studs. With a bit of overkill for this normally aspirated application, they would come in handy once we applied boost from our Vortech supercharger.

The PI components lived up to their names, as the ported heads, cams, and intake increased the power output of our '97 Two-Valve motor from 258 hp and 341 lb-ft of torque to 401 hp and 390 lb-ft of torque. The graph tells the whole story; instead of leveling off at 4,000 rpm, the new components allowed the motor to pull strongly to 6,000 rpm. Thanks primarily to the wilder cam timing, there was a slight drop in power below 3,500 rpm, but the gains from 3,500 rpm all the way to 6,000 rpm were tremendous. Imagine: the heads, cam, and intake improved the power output of this early Two-Valve motor by 143 hp. How full does that glass look now?

While the gains offered by the top-end package were impressive, there was more power to be had with the introduction of forced induction. Turning to Vortech, we opted to install one of the company's 4.6 GT kits that included an air-to-water intercooler system. Though we purposely limited the boost level with the stock short-block (cast pistons), we deemed the charge cooler necessary due to the elevated compression ratio of our hybrid PI motor. We also took the liberty of adding a can of Lucas Oil octane booster to the Rocket Brand premium unleaded pump gas.

We installed the Vortech supercharger on the awaiting motor using a combination of the factory crank and 3.33-inch blower pulley. The net result was a maximum boost level of 10.9 psi at 6,400 rpm. Running dyno water through the charge cooler, the supercharged combination produced 648 hp and 543 lb-ft of torque. From the looks of the power curve, had we not limited our high-mileage, stock short-block to 6,500 rpm, the power curve would still climb rapidly. With a more aggressive tune (more timing), a cooler charge from ice water, and elevated engine rpm, this could be one serious motor. We certainly recommend forged internals for such an exercise. As it is, any glass that contains an early Two-Valve 4.6 motor that pumps out nearly 650 hp is neither half empty nor half full-it's completely full.

On The Dyno
It should be obvious from the shape of the factory curves that torque production was foremost on the minds of the mod-motor engineers when they designed the original 4.6 Two-Valve motor. This high-mileage '97 motor produced only 258 hp at 4,800 rpm, although the power curve exceeded 250 hp from 4,000 rpm to 5,200 rpm. The torque peak of 341 lb-ft occurred at 3,500 rpm. From behind the wheel, these early Two-Valve motors feel fairly responsive, but the party dies quickly with additional engine speed. Replacing the stock intake, cams, and heads with the ported PI heads, Xtreme Energy cams, and PI intake resulted in serious power. The improvements in flow, compression, and cam timing increase the peak power numbers from 258 hp and 341 lb-ft of torque to 401 hp and 390 lb-ft of torque. Note that the wilder cam timing effectively shifted the torque curve to allow the peak power output to occur at 6,000 rpm rather than 4,800 rpm. The peak torque shifted likewise, from 3,500 rpm to 4,900 rpm.

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