Tom Wilson
April 6, 2011

Horse Sense: In case you just tuned in and are wondering what all this animal talk is about, Ford often tags its in-development programs with a code name. You’d have to be living under a 4.6 block not to know the latest 5.0-liter was code-named Coyote. However, you might easily have forgotten that the GT500 program was code-named Condor, hence our little bit of canine-versus-bird alliteration.

We’re fond of saying there is no replacement for displacement, because, in the end, there isn’t. However, supercharging and refinement do much to overcome the advantage of large engine displacement, a fact brought to our attention by Jim Bell at Kenne Bell.

Clearly Jim is happy to tout the advantages of his popular twin-screw blowers, but we had to admit a comparison of his two most recent projects--adding a supercharger to the 5.0 Coyote engine in the Mustang GT and upgrading the Shelby GT500 to a Kenne Bell Twin Screw--illustrate how the smaller, lighter 5.0 ultimately makes more snort than the rip-roaring Shelby.

There is no new hardware involved in this story, as we recently introduced the 2.8 Kenne Bell Twin Screw blower on the new GT, and the 2.8 blower on the Shelby is well known at this point. What we haven’t mentioned, and why Kenne Bell just had an ’11 GT500 in its shop, is the current Shelby uses the same engine management system as the Coyote-powered GT. Thus, Kenne Bell was burning midnight oil getting its electronic tune on the ’11 Shelby, which is how the company got started comparing the Shelby and GT outputs.

With few hardware differences between the ’11 GT500 and earlier models, both the KB-tuned ’11 and earlier GT500s make the same power. On KB’s dyno, that means the ’11 GT500 measured 481 rwhp stone-stock, and ran up to 689 rwhp at 18 pounds of boost with the KB blower. For the Coyote-powered Mustang GT, Kenne Bell had a variety (hundreds) of dyno runs gathered by both manual- and automatic-transmission ’11 GTs. Picking through the data allowed some reasonable apples-to-apples comparisons with the GT500. We’ll admit this did require a sharp eye on things such as throttle body size and so on, but with so much data to work from, we’re comfortable making the comparisons.

To get right to the point, at just under the 9 pounds of boost, the stock GT500 was at 481 rwhp and the 5.0 Mustang GT with the KB blower hit 547 rwhp. This is an Eaton-to-Kenne Bell comparison, which accounts for some of the huge power differential, but it shows how eagerly the Coyote responds to boost. At 12 pounds of boost, the manual-transmission GT500 laid down 615 rwhp, while an automatic trans Mustang GT came in with 657 rwhp. At 15 pounds of boost, the same pair of cars were 654 rwhp for the Shelby and 720 rwhp for the GT. There was no higher GT boost pressure available at our deadline, but the Shelby was cranked up to 18 pounds of boost and 689 rwhp, where even with a manual transmission, 2 extra pounds of boost, and 400cc more displacement, it still came up about 30 rwhp shy of the GT. Hmmm...

Granted, the above summation is far over-simplified, if for no other reason because it compares just peak power figures, but the direction is clearthe smaller 5.0 makes more horsepower than a 5.4. Why is this? Shouldn’t Ford’s top-dog Mustang engine eclipse its smaller brother?

Well, at first glance, the two engines are quite similar. Each is an all-aluminum V-8 with four valves per cylinder, double overhead camshafts, and performance tuning from the factory. Their basic internal dimensions are also similar, but differ in at least one key standpointstroke. Where the 5.0 stroke is 3.563-inch, the 5.4 gains the majority of its displacement by swinging a longer 4.165-inch-stroke crankshaft. And that longer stroke means a faster piston speed, and consequently a lower redline.

Now, with enough expensive parts, it’s possible to rev a 5.4 with Formula 1-like piston speed--witness the ’00 Mustang Cobra R. It redlines at 6,500 rpm with a fuel shut-off at 6,800 rpm, and if that doesn’t do it, the ignition cuts off at 7,000 rpm. Of course, this most exciting of Mustang engines was expensive and rare--only 300 produced. The Shelby GT500 on the other hand, is less exotic and redlines at 6,250 rpm.