Increased compression was the first step toward improving the power output of the normally aspirated combination. Improving the NA power would actually reduce the boost pressure supplied to the engine (at any given drive ratio). The elevated compression ratio was combined with slightly wilder cam timing in the form of a set of Comp XE262AH cams. The Comp cams offered 0.425 lift and a 226/22 duration split that favored the intake side. Having tested these cams before in our "Mods for Four-Valve Mods" series (and this author's new book on modular performance), they work well on the Terminator engines despite not having more exhaust duration as is typical of blower cams. To make the most effective use of the newfound lift and duration, Mihovetz worked some of his magic on the Four-Valve cylinder heads as well.
Naturally, there was some minor porting involved, but according to Mihovetz, the real key is to have the valve guides properly sized, the valve job spot on, and the all-important valve height/lash adjuster relationship optimized. These lessons (along with a few we were sworn to secrecy over) were learned over a decade of campaigning modular motors. Even without the porting, the tricks performed to the Four-Valve heads can yield 30-50 hp on his wild turbo combination. Though the gains may be less on this somewhat milder supercharged motor, every bit helps when you are looking to maximize the power output of any given combination.
While testing for our "Mods for Four-Valve Mods series," we ran the 2.2L blower from Kenne Bell. With the larger 2.4L blower available, we naturally stepped up to this configuration to maximize the airflow potential of the blower. The 2.4L twin-screw supercharger offered a 9-percent increase in displacement, and therefore increased the flow potential over the smaller 2.2L blower. It was fed by an Accufab oval throttle body and the Kenne Bell blower inlet.
This last bit of info is important as we tested a modified version of the blower inlet with excellent results. In the car, the engine was equipped with a set of Kooks 151/48-inch long-tube headers featuring 2.5-inch collectors. Mihovetz suspected these might be a tad on the small side for this application, so we had a set of Hooker headers (same 151/48-inch primaries but with 3-inch collectors) and a set of (171/48- to 2-inch) race headers from his early supercharged race motor ready to go.
The supercharged 4.6 was also equipped with a Dial-Ur-Boost (DUB) crank pulley assembly from South Florida Pulley Headquarters. Naturally, the Kenne Bell blower pulleys were also inter-changeable, allowing us to dial in the blower speed and attending boost pressure at will. The blower assembly also included the factory '03 Cobra air-to-water intercooler assembly. For dyno testing, we relied on the dyno water for the intercooler, but stepped up to ice water for the last runs on this combination.
The Four-Valve 4.6 was installed on the dyno in normally aspirated trim to allow for proper break-in. The motor was filled with Lucas conventional (non-synthetic) 5W-30 oil and equipped with 36-pound injectors. The FAST engine management system was used to dial in the air/fuel mixture, and we were eventually rewarded with over 400 hp and nearly as much torque.
These power numbers were actually down quite a bit from what was expected and there was evidence of blow-by. It should be noted that the engine was subjected to a minor mishap during the initial break-in procedure. An air pocket kept water from circulating in the block, allowing the Four-Valve motor to get hot enough to boil the water in the block. All the tempo gauges (both on the dyno and in the FAST management system) showed the water temp to be, if anything, on the low side. The problem was that they were reading air and not water. Did the overheating torch the rings, or were the stainless rings simply reluctant to break in? Concerned about the condition of the freshly built motor, we pressed on with our testing after a compression test revealed that all eight holes were still present and accounted for.
Na vs. Kenne Bell Supercharged...
Na vs. Kenne Bell Supercharged 4.6L four-valve Motor (9.2 psi and 19.9 psi) - We began this adventure by running the modified '03 Cobra 4.6 in normally aspirated trim. This was done both to establish a baseline and allow some break-in time for the rings and bearings. The NA version produced 416 hp and 393 lb-ft of torque. While this was less than expected, we installed the Kenne Bell blower and ran it at 9.2 psi where the engine produced 570 hp and 488 lb-ft of torque. Stepping things up to 19.9 psi with a 3.75-inch blower pulley brought the peak power to 767 hp and 698 lb-ft of torque.
Stock (KB) vs. Modified Blower...
Stock (KB) vs. Modified Blower Inlet - Suspecting that the inlet supplied with the Kenne Bell supercharger kit may become a flow restriction at these elevated power levels, Mihovetz modified one of the aluminum intakes to increase the flow rate. After porting and welding, the revised intake (from the throttle body to the inlet of the blower) improved the power significantly, upping the peak numbers to 800 hp and 704 lb-ft of torque. Note that most of the power gains offered by the revised inlet occurred at the top of the rev range.
The '03 Cobra heads received...
The '03 Cobra heads received minor porting to improve the flow potential.
A SerDI machine was used to...
A SerDI machine was used to produce a concentric valve job (critical for proper valve sealing). The heads also received new guides to eliminate run-out that will also hurt valve seal.