Both the intake and exhaust ports received extensive CNC porting to improve the flow poten
While we had come up shy after combining the new CHP short-block with the FSP ported heads, we still had at least one ace up our sleeve in the form of more aggressive cam profiles. Until now, both the original 200,000-mile and new CHP/FPS combinations were run using the XE262H cams supplied by Comp Cams. As with all of the non-PI cams, the XE262H cams featured 0.500-inch lift. The smallest of the Xtreme Energy grinds for the early Two-Valve modular motors offered a 224/232 duration split (at 0.050) and a 114-degree lobe separation angle. While we liked the combination of power and driveability offered by the XE262H, we knew there was more power to be had with a larger cam profile.
To that end, we selected the largest of the XE series, the XE274H. These cams offered the same 0.500-inch lift, but increased the duration split from 224/232 to 236/240 degrees. Both cams featured the same 114-degree lobe separation angle. Installation of the larger XE274H cams took less than 1 hour (we've become pretty proficient at cam swaps on the Two-Valve motor), and in no time the mod motor was ready for tuning. Running the same air/fuel and timing (13.0:1 and 30 degrees total), the XE274H cam increased the peak power output to 317 hp and 349 lb-ft of torque.
The new cam profiles offered decent power gains, but we were actually expecting a bit more given the change in duration. At 6,000 rpm, the largest gain was 17 hp, but the all-important peak-to-peak gain was just 9 hp. That extra 9 hp brought us that much closer to achieving our 300hp goal, but it was not without cost-namely, some low-speed torque and, more importantly, driveability. Compared to the smaller XE262H cams, the larger X274H profiles lost power up to 4,100 rpm. Though the losses were never more than 9 lb-ft, the daily driver status of this project car means we will be running the motor where we experienced a power loss much more than where we experienced a power gain.
Before installing the 4.6 back in the awaiting '96 GT, we decided to try one final upgrade. With limited parts available for the early (non-PI) motors, I took it upon myself to design an intake manifold for the early Two-Valve motors. Remember that this intake design was tested in prototype form, and we (the magazine) will reserve judgment until a production version can be properly tested. But the results were pretty impressive-even more so considering the prototype intake was actually designed for the later PI head, thus resulting in a significant port mismatch between the PI and non PI components.
The chambers also received some polishing, not to mention a set of new SI stainless steel
The mismatch notwithstanding, the intake was secured to the non-PI heads and run in anger on the engine dyno. Equipped with the new intake design, the peak power jumped from 317 hp to a whopping 355 hp at 6,200 rpm. Even more impressive was that the intake design did not lose any power down low (as is often the case). The intake design improved the power output from 2,900 rpm (the lowest test point) through 6,500 rpm, registering gains as high as 50 hp over the stock non-PI intake.
Though the torque gains were most signifi-cant past 4,800 rpm, at 3,800 rpm the intake increased torque production by 24 lb-ft. Look for a production version to appear on the 4.6 for chassis dyno testing as we (hopefully) finalize the quest for 300 hp and can finally step up to forced induction.
We installed the engine back in the car for a shot at the chassis dyno. After installation and tuning, the fresh combo put down 276 hp and 315 lb-ft of torque. Finally, a significant step toward our goal of 300 hp.
Both Fel-Pro and ARP helped out by supplying new head gaskets and head studs to secure our
The original and new CHP/FPS motors were run with the XE262H cams, but we planned on upgra
Following a break-in period, the new 4.6 combina-tion produced 308 hp at 5,200 rpm and 347