 Early 4.6 four-valve N/A vs....  Early 4.6 four-valve N/A vs. Kenne Bell (9 psi)
Our early 4.6 Four-Valve test motor was nothing special, just a high-mileage '96 motor equipped with Hooker headers, a Meziere electric water pump, and recently installed Comp XE262AH cams. Run on the FAST management system, the early Four-Valve motor produced 375 hp and 342 lb-ft of torque in normally aspirated trim. Installation of the Kenne Bell twin-screw supercharger kit was easy on the engine dyno, and managed to provide just over 9 psi to the hungry Four-Valve motor. Though lacking the intercooler available on the later Cobras (thanks to the factory '03-'04 setup), the nonintercooled Kenne Bell kit upped the peak power numbers to 486 hp and 433 lb-ft of torque. As expected, the torque gains offered by the positive displacement kit were immediate and impressive, with well over 100 extra lb-ft of torque at 3,500 rpm. |
 The normally aspirated motor...  The normally aspirated motor was run with 36-pound injectors, while we stepped up to 65 pounders after installing the supercharger. |
 Meziere shipped us a new electric...  Meziere shipped us a new electric water pump complete with idler pulley that allowed us to run the water pump with a serpentine belt. |
 Hooker long-tube headers feeding...  Hooker long-tube headers feeding an 18-inch collector extension were used on both the N/A and blown motor. |
One of the reasons we decided to include a separate "Mods for Early Four-Valve Mods" was because the early motors differed from their late-model counterparts. Though they share similar short-blocks, which displace 4.6 liters, the heads and intake manifolds are substantially different. This difference was one of the reasons why the early Four-Valve motors required a different kit from Kenne Bell. Where the late-model Cobras can enjoy an intercooled kit similar to the one used on the '03-'04 Cobras (but with the more efficient twin-screw blower), the kit for the early Cobras comes sans air-to-water intercooler. What this means is that an early Cobra will not likely produce as much power as a late-model one equipped with an inter-cooled kit, but an early Cobra owner should be able to equal or surpass the power offered by a stock '03-'04.
After all, the difference in the rated power output between the early Cobra and the '03-'04 was only 90 hp. Despite the lack of the inter-cooler, we had high hopes for the blower kit on the '96 Cobra motor. With the exception of the nitrous, none of the normally aspirated mods made much of a power difference, at least not compared to a blower.
The Kenne Bell twin-screw blower kit for the '96-'98 Cobras featured a 1.7L super-charger. While Kenne Bell also offers larger blowers for more serious power gains, we have exceeded 600 rwhp with the 1.7L unit, so we have no fear about the power potential. Since the supercharger was driven off the six-rib serpentine belt shared by the rest of the engine accessories, we had to rig up a drive system using a borrowed A/C compressor, the Meziere idler water pump assembly, and the factory belt tensioner.
After measuring the proper belt length, it took only four trips to the local auto parts store to finally arrive at a suitable belt length. Having the belt extra tight provided us the room to drop down in pulley size for even more boost pressure. Driving the blower was the factory crank/damper, but Kenne Bell also offers larger crank pulleys as well. The larger crank pulley will allow you to increase the blower pulley size (while retaining the same drive ratio), which helps eliminate belt slippage. Increasing the crank pulley also increases the speed of the engine accessories, which will reduce power slightly (though not nearly as much as the extra power provided by the increase in boost). For our runs, we equipped the blower with a 3-inch blower pulley, which produced just over 9 psi of boost.
To ensure adequate fuel delivery, the 36-pound injectors run on the normally aspirated motor were replaced with a set that flowed 65 lb/hr. A Kenne Bell Boost-a-Pump and Boost-a-Spark were employed on the engine dyno to ensure adequate voltage supply to the fuel pump and ignition system. Denso IQ16 Irridium spark plugs were replaced by a set of colder IQ24s. Colder plugs are necessary when running boost, especially on a blower kit not equipped with an intercooler.
After some tuning on the FAST manage-ment system (by Westech's Tom Habryzk), the supercharged combination produced 486 hp and 433 lb-ft of torque. As we have come to expect of a positive displacement supercharger, the Kenne Bell kit offered immediate boost response and a ton of torque right along with it. Down at 3,500 rpm, the blower improved the torque production by over 120 lb-ft. While the extra 110 hp is what everyone talks about, it is this extra torque that is most often enjoyed from behind the wheel.
You know how we roll at MM&FF, so you don't think we could just stick the Four-Valve motor on the dyno and run it at just one boost level, right? Pulley swaps on the Kenne Bell are so easy, we decided to replace the 3-inch pulley with a smaller 2.75-inch version. Of course, the extra boost (a tad over 12 psi total) required some minor tuning (thanks for staying late, Tom). We were rewarded with peak power numbers of 506 hp and 463 lb-ft of torque. It should be noted that we hedged our bets with the stock cast pistons by topping off the fuel tank with 100-octane race fuel.