Tom Wilson
December 20, 2006

While Jim Bell's Kenne Bell started the whole twin-screw blower scene in the United States back in the Buick Grand National and 5.0 H.O. days, the pivotal event in his modern era was the five-day '03 Mustang Cobra test we reported on a couple of years ago. By swapping the Cobra's old-tech Roots supercharger for a far more efficient twin-screw, Jim treated us all to 617 rwhp in an otherwise frighteningly stock Terminator.

It was crazy stuff. With just an open air inlet, open exhaust, electronic tuning, 20 pounds of boost, and a splash of race gas, the Cobra was making race power with a totally internally stock engine, stock exhaust manifolds, and stock cats. At the time, it was unnervingly easy to make such power, and even after these antics have become almost commonplace it's still a wonder how the modern engines make such big power. We chalked it up to the fancy Four-Valve cylinder heads, good manifolding, and all the rest that comes with a top-dog Cobra.

Kenne Bell's Two-Valve project is sano, with a minimum of extraneous flash for the confidently powerful look. The polished canister next to the alternator is the water-to-air charge-cooler reservoir. It fills through the small plug in its top, so there is no icing it down. The reversed alternator shows how the supercharger and other accessories share the same serpentine belt.

Perhaps even more amazing is Kenne Bell has repeated, actually surpassed, the performance with the yellow Two-Valve smoking its way across these pages. Granted, it took a prepped short-block and ported cylinder heads to reach the power stratosphere set by the Cobra, but still it's an amazing thing to see what the popular '99-'04 GTs can do with a bit o' boost.

About 642 rear-wheel horsepower is what it can do, but what it takes to get there is a slightly longer story. To make three times stock power in a Two-Valve GT engine, Jim Bell began with a '99 Mustang GT, a "program" car from Ford that Bell used for development of his Two-Valve supercharger and even glamour duty at the SEMA show. Once the basic Two-Valve kit was developed, Jim, electronics expert Ken Christley, and dyno technician, track driver, and all-around wrench Brent Morris kept right on going building power.

Getting enough fuel to the engine is often trouble with the newer Mustangs when reaching the mid-500-rwhp mark. Then it's easiest to exchange the stock GT fuel tank, pumps, and controllers for the Cobra version. Electronic control issues will also arise, although the '99-'04 Mustangs were still given cable-activated throttles, so the electronic throttle plague is not a factor here.

There are real physical limitations of the Two-Valve engine. The good news is these engines boast strong blocks, crankshafts, heads, sport a good oiling system, and generally are surprisingly durable. The bad news is the stock pistons and powdered-metal connecting rods are good for 450 rear-wheel horsepower, according to Jim. After that, you need an all-forged aftermarket short-block.

Only a few pressures and temperatures are needed to monitor the underhood goings-on. Of these, boost literally gets top billing.

Kenne Bell's Two-Valve goal was to reach the mid-600-rwhp level, enough to match the Mustang Cobra. If the sun and moon aligned, they also wanted a 9-second timeslip. Furthermore, we haven't mentioned that the big power was being mated to an automatic transmission, making the performance goals more difficult due to the reduced efficiency of the automatic transmission.

For performance and longevity, KB had the 4R70W automatic authoritatively prepped by Jerry Wroblewski and Precision Industries of Oakland, Tennessee. Besides the usual high-strength internal modifications, this transmission was wearing an approximately 2,400- stall torque converter and was rigged to manually lock the torque converter. This was done for performance reasons-it posted 6.5 percent more power when locked up-and to provide repeatability on the dyno.

As we've previously detailed Kenne Bell's standard Two-Valve supercharger kits, we'll only review them here as stepping stones to the big power. The first step is KB's 1.7-liter supercharger kit at low boost and no charge cooling, followed by the same kit with charge cooling and 9 pounds of boost. Supporting pieces at the 9 pounds of boost level are a 90mm mass air meter, a 75mm throttle body, and a 75mm cold-air inlet. Power is 431 rear-wheel horsepower on the stock short-block and using a manual transmission.

A drag slick is always a good idea, and absolutely the only way to deal with more than 600 hp at the tires. Even so, the best short time to date is a 1.54-second squirt, which could be improved with more chassis work given this much power. The wheel is a 15x10-inch Colorado Custom Yuma.

While well past the 1.7-liter blower's best efficiency, stepping this kit all the way up to 15 pounds of boost with a simple pulley change gives 507 rwhp with the manual transmission or 476 rwhp with the automatic. It also triggers the need for a prepped short-block-meaning KB's stocker went bang on the dyno-and Kenne Bell therefore repaired its yellow tester with a Sean Hyland unit featuring 8.1:1 forged pistons.

In fact, the engine and chassis were prepped at this time to support the expected 650-plus rear-wheel horsepower. Renegade Racing ported the Performance Improved cylinder heads rather extensively, and Comp Cams XE274HR cams and matching springs were fitted. The fuel system was upgraded to '03 Cobra returnless specs. That would be the internally baffled Cobra fuel tank and its dual fuel pumps, plus an extra 1?4-inch fuel line and filter plumbed into the stock fuel rails, making both rails plumbed directly to a fuel pump. The injectors are 60-lb/hr units, and the stock rails are large enough and are thus retained. Initially the ignition was stock, but at high power one of KB's Boost-A-Sparks is necessary. Both Denso and narrowly gapped NGK spark plugs were used, and the exhaust benefited from long-tube Hooker headers, a Bassani non-cat X-shape exhaust crossover, and an after-cat system.

Naturally, the induction centered around a Kenne Bell supercharger, which was moved up to a 2.2-liter Blowzilla to regain the necessary blower efficiency. Kenne Bell's 5-inch Cool Air kit and a Kenne Bell Big Oval throttle body-a Cobra throttle body with the twin-bores machined out and a single, large oval throttle plate fitted-assured no induction loss on the naturally aspirated side of the blower. The 90mm mass air meter remained.