Richard Holdener
March 11, 2015

The Ford mod motor evolved from humble beginnings into the amazing Coyote and 5.8L GT500 motors we have today. With the normally aspirated, 5.0L Coyote up at 420 hp and the 5.8L GT500 mil pumping out 662 hp, mod motors have reached serious power levels. Today’s mod motors have come a long way since the introduction of the OHC 4.6L in 1996 (in the Mustang). Midway between the original non-PI 4.6L and today’s modern muscle was the 4.6L Three-Valve. When introduced, the Three-Valve brought on variable cam timing to the mod motor family, possibly to make up for the lack of the extra exhaust valve (compared to the Cobra motor). The variable cam timing allowed the Three-Valve to combine four-valve peak performance with superior average torque production. Unfortunately for owners of 2005-2010 models, when Ford reintroduced the famous 5.0L (Coyote), the Three-Valve was set on the past performance shelf next to the PI Two-Valve and B-headed four-valve.

Fear not, Three-Valve fans. We have one simple addition that can significantly increase the output of your 4.6L. We all know that mod motors respond well to boost, and the Three-Valve is no exception. We all recognize that in the mod-motor hierarchy, the Three-Valve was already significantly better than either of the Two-Valve motors. An argument might even be made that the variable cam timing offset the missing valve offered by a four-valve Cobra motor. The upshot of this discussion is that the Three-Valve can make serious power with nothing more than a blower upgrade. Big deal, you say? Everyone knows a blower will add a ton of power, you say? While it is not surprising that a supercharger will significantly increase the power output, what is surprising here is the definition of significantly. How much power does it take to impress Three-Valve owners? 100 hp, 200 hp, or how about 300 hp? What if we told you the blower upgrade was worth over 500 hp (a gain of nearly 200 percent), all with stock heads, cams and compression?

By now, all the Three-Valve owners should be salivating, and if not, we can direct you to a couple of nice feature articles in the latest issue of Cat Fancy. Think about it. This Kenne Bell twin-screw blower upgrade improved the power output of the 4.6L Three-Valve from 285 wheel horsepower (whp) to over 805, but, as always, that was only part of the story. Through extensive testing, Kenne Bell has managed to come up with different stages and upgrades catering to anything from a stone-stock motor to a fully built race machine. Naturally all of these upgrades were dyno verified, starting with the Stage 1 Kenne Bell kit that featured the 2.6L twin-screw supercharger. This kit included KB’s patented Boost-A-Pump (BAP), 42-pound injectors, and precision calibration to allow 8.5 psi of boost that increased the power output of the Three-Valve from 285 to 509 hp (using 91-octane fuel). Stage 2 added a high-flow, 130mm throttle-body that upped the boost pressure to just over 9 psi, where the combination pumped out 526 whp.

The Stage 2 system was capable of much more power, but things get serious when you step up to the larger 2.8L blower and Mammoth intake. With no change in the 2.6/6.5-inch pulley combination, this pushed peak pressure to 10 psi and power to 566 whp (on 93-octane). Given that the 2.8L will support over 1,000 hp, it is possible to up the power output with nothing more than a pulley swap.

The highlight of the blower upgrade was the efficient Kenne Bell twin-screw supercharger.

Since we went looking for big-time power out of this Three-Valve motor, internal changes were made to facilitate the new power level. The stock test motor was turned over to Sean Hyland Motorsports (SHM) for fortification. The order from Kenne Bell was to keep every parameter stock, just upgrade the internals to withstand the elevated boost and power levels. SHM obliged with a Teksid block stuffed with a Cobra crank, forged rods, and pistons. The rotating assembly retained the stock displacement and compression, and to this SHM installed a set of as-cast (stock) Three-Valve heads, cams, and intake manifold. Basically the motor was a forged stocker, capable of withstanding the 25-plus psi of boost required to reach the 800hp goal. However, it should be noted that the SHM forged test motor produced within 2 hp of the factory Ford motor in normally aspirated trim.

The internally fortified SHM motor received a few additional modifications before the boost was cranked up. First on the list was a Centerforce clutch, as the stock one was not happy with big boost. Next came a Meziere electric water pump (good for as much as 25 hp during testing), which eliminated pump cavitation caused by the oversized crank pulley from ATI required for the elevated boost levels. The blower/crank pulley combination was altered to increase the peak boost pressure to 20 psi, and the tank was filled with C16 race fuel. The stock fuel pump/BAP and 42-pound injectors were ditched in favor of a dual-pump system from the Shelby GT500 and a set of 1,000cc squirters from Injector Dynamics. As with the stock pump, the Shelby system was augmented with a 17V Kenne Bell BAP. Even with the stock fuel lines and rails, the new fuel system was capable of supporting over 800 whp and can be upgraded to 1,000 hp with the addition of a 20V BAP. Equipped with a 6.5-inch crank pulley and 3.0-inch blower pulley, the supercharged Three-Valve produced 716 hp and 614 lb-ft of torque.

The next test involved replacing the C16 race fuel with E85. Pumped right from the local station, the E85 offered an increase in power (with no change in pulley ratio or boost) to 743 hp. This came with the same Lambda mixture and timing, meaning additional power was available with a slightly leaner mixture. Compared to a safe tune (timing and fuel) and boost level on pump gas, the E85 upgrade was worth an extra 11 psi and nearly 200 hp. Think about that for a minute. The E85 offered a reduced caloric content, meaning it took more fuel to make the power, but the big benefit was the effective octane rating that allowed us to safely and dramatically increase the boost pressure. The fuel system was up to the task of supplying the additional E85 fuel at this power level, and tune was easily altered to accommodate the E85. This particular Mustang was driven daily (for the last two years) on E85 with excellent results, and woe to any Camaro or Corvette who tries to best this little Three-Valve GT!

The final test involved a switch back to C16 (though the power is possible on E85). The pulley ratio was once again altered to increase boost with the installation of a 2.75-inch blower and 7.5-inch crank pulley (drive ratio of 2.73:1). This blower speed resulted in a peak boost pressure of 26 psi where the supercharged Three-Valve produced 805 hp and 746 lb-ft of torque. There was a touch of clutch slippage on this run, which may require even more clamping force to continue testing at elevated power and boost levels.

What did we learn from this test besides some new mod-motor math that shows that three V (valve) plus B (boost) equals serious HP? We learned the flow potential of the stock fuel lines and rails, the amazing ability of a BAP, and the importance of minimizing intake restrictions. Even more amazing was the fact that all of this power was channeled through the stock exhaust manifolds and cats.

1. The standard (Stage 1) kit included a 2.6L blower and was good for 509 whp (up from 285) at 8.5 psi (using 91-octane, more with 93-octane).

2. The Stage 1 kit featured a fuel system upgraded that included a (boost-activated) Kenne Bell Boost-A-Pump feeding a set of 42-pound injectors. This simple but effective fuel system upgrade was capable of supporting over 650 whp.

3. The inlet on the Stage 2 kit accepted a larger throttle-body that increased boost by roughly 0.5 psi. The result was a jump in power to 526 whp (still on 91-octane). The 2.6L will support nearly 1,000 hp, but for serious power the larger 2.8L Mammoth kit is the way to go. Note the difference in the inlet on the larger (polished) supercharger.

4. Regardless of the displacement of the supercharger, each featured a dedicated air-to-water intercooler. Cooler charge temps reduce the chance of detonation and allow increased boost levels for any given octane rating.w

5. Positive displacement superchargers are very sensitive to inlet restrictions. The best supercharger in the world won’t produce boost if you can’t feed it the necessary airflow. Kenne Bell offered a wide range of throttle body upgrades, including the massive 168mm oval blade that flowed 2,150 cfm, which is enough to support 1,500 hp.

6. It is hard to believe that all of the supercharged power was sent through these stock exhaust manifolds.

7. Testing with the cats revealed that they were worth as much as 20 hp at the 750hp level.

8. To increase power and cooling and eliminate the cavitation of the stock water pump, Kenne Bell added this Meziere electric water pump.

9. In addition to the air-to-water intercooler, the Kenne Bell supercharger featured liquid cooling technology to reduce the temperature differential between the (cool) inlet and (heated) discharge sides of the rotor pack.

10. To maximize power, the SHM 4.6L, Three-Valve test motor was equipped with a 2.8L Mammoth supercharger kit and 168mm throttle body.

11. Increasing the boost was a simple matter of changing the blower and/or crank pulley to speed up the supercharger. The boost was cranked up as high as 20 psi on E85 and 26 psi race gas.

12. Kenne Bell’s own Ken Christley was on hand to ensure that not only did the Three-Valve make the necessary power, but it did so with acceptable street manners. No easy task on a daily driven GT using E85, 1000cc injectors, and 20 psi of boost.

13. With the Centerforce clutch holding on for dear life, the supercharged GT pumps out an amazing 805 whp and 746 lb-ft of torque. After we saw these numbers generated with the stock heads, cam, and intake and the 2.8L supercharger, talk immediately turned to stepping up the program with ported heads, Comp cams, and the larger 3.6L.

Kenne Bell Supercharged Three-Valve Test Results
Blower Size KB Kit Octane Peak Boost WHP Pulley Sizes Notes
n/a (stock) n/a 91 0 285 n/a
2.6L Stage 1 91 8.5 509 3.6/6.5
2.6L Stage 2 91 9 526 3.6/6.5 Larger TB
2.8L Mammoth 93 10 566 3.6/6.5 Larger SC & inlet
2.8L Mammoth C16 20 716 2.75/6.5 Blower pulley
2.8L Mammoth E85 20 743 2.75/6.5 E85
2.8L Mammoth C16 26 805 2.75/7.5 Crank pulley