Richard Holdener
August 1, 2005
It was great to get the '05 Three-Valve GT on the chassis dyno, especially since we knew we were going to get to test the new Kenne Bell supercharger kit.

For me, the glass is almost always half full. Here it is 2005, and I have a great job where I get to build all manner of high-performance machines, a wonderful wife who supports my chosen profession, and even a new baby on the way. To top things off, Ford went and introduced what is one of the best-looking Mustangs to ever roll off the assembly line.

In addition to the drop-dead good looks, the '05 was blessed with what is arguably the most powerful motor ever to grace the simple GT. Despite the differences in the gross-versus-net power ratings, it would take a good-running 428 Cobra Jet to keep up with a new 281-inch Three-Valve GT.

As impressive as the new 4.6 Three-Valve GT motors are, the glass-is-half-empty side of me can't resist pointing out the fact that noticeably absent in '05 Mustang offerings is a Cobra, or, more specifically, a supercharged Cobra. A case can certainly be made that the Three-Valve can all but replace the normally aspirated Four-Valve powerplant, but all the extra valves and variable cam timing in the world won't make up for the missing supercharger available on the '03-'04 Four-Valve Cobra 4.6s. Luckily for us, the gang at Kenne Bell specializes in filling that half-empty modular performance glass. Enter the Three-Valve supercharger kit.

The most important part of the new Kenne Bell blower kit for the '05 Three-Valve GT was the Autorotor twin-screw supercharger. Offering immediate boost response and improved efficiency compared to a typical Roots-style blower, the twin-screw was capable of supporting over 500 hp.

Naturally, we all welcomed the power increase from 260 hp to 300 hp offered by the new Three-Valve configuration of the familiar 4.6. The extra 40 hp has been a long time coming, but can the normally aspirated Three-Valve really be expected to take the fight to the 5.7-liter LS1s of the world? Despite the new 300hp rating, the larger 5.7 LS1--to say nothing of the new 400hp 6.0 LS2--will easily dispatch the Three-Valve GT.

With the introduction of the supercharged 5.4 Cobra a year or so away, Mustang enthusiasts are temporarily sans factory supercharging, but the aftermarket is always willing and able. Kenne Bell has long been associated with supercharging Mustangs, way back to the 5.0 days. Its offerings for the 4.6 include the early and late Two-Valve and most models of the Four-Valve Cobra (including Mach 1).

Kenne Bell really came into its own when Ford introduced the supercharged Lightning and then the supercharged Four-Valve Cobra. Factory equipped with positive-displacement Eaton superchargers, enthusiasts soon found that the route to huge power from their Lightning or Cobra motor was with a Kenne Bell blower upgrade. Simply replacing the factory Eaton M112 supercharger with a more efficient and powerful Autorotor twin-screw blower resulted in big-time power gains. Where the supercharged Cobra guys struggled to eclipse 500 wheel horsepower, some '03-'04s equipped with the twin-screw blower were soon besting 700 wheel horsepower and dipping into the nines, all without resorting to nitrous.

The new Kenne Bell kit came equipped with a 2.75-inch (six-rib) blower pulley to work with the stock 6.5-inch crank pulley. The pulley combination provided 9 psi of boost to the 4.6 mod motor.

All that supercharged experience with the previous mod motors has paid off in the form of a new kit for the Three-Valve 4.6 used in the '05 GT. Given the near (normally aspirated) Four-Valve Cobra performance from the Three-Valve 4.6, it's not sur-prising that Kenne Bell was able to not only reach the power output of the '03-'04 super-charged Four-Valve engine, but surpass it.

Installation of the Kenne Bell blower kit on the Three-Valve Ford pushed up the rear-wheel power output from 268 hp to 459 hp. Think about it--a gain of 191 hp with just 9 psi of boost. As we have come to expect, the Three-Valve super-charger kit from Kenne Bell is somewhat more involved than just plopping a blower in place of the factory intake. The days of building a suitable blower mount (for a centrifugal) or an adapter plate (for a Roots-style or twin screw) and combining it with an FMU are long gone. Blower kits (at least complete ones) have become a serious undertaking.

In the case of the new Kenne Bell Three-Valve kit, the serious undertaking included not only the required ECU recalibration (no easy task given the combination of drive-by-wire throttle and variable cam timing), but also a dedicated air-to-water intercooler. Included in the Kenne Bell Three-Valve kit is an air-to-water intercooler located in the lower intake manifold. The pressurized air is fed by the (already efficient) twin-screw blower though the intercooler, the lower intake, and finally to the cylinder head ports. Like the system used on the factory supercharged Four-Valve Cobra, the Kenne Bell air-to-water intercooler system employed a front-mounted heat exchanger to dissipate the unwanted heat to the atmosphere.