Check out the sidebars at the end of the article to get the details on each step of the bo
The new 4.6 two-valve Mustang makes 235 hp to the rear wheels. In this age of superchargers, nitrous oxide, and advanced cylinder head and camshaft development, 235 rear-wheel hp is nothing to get excited about. But considering that number is roughly 45 hp more than what the '98 4.6 made (about 190), you begin to appreciate how Ford is trying to help its 4.6 gain respectability in the performance market. What's even more impressive is how the much-maligned 4.6 stacks up against the traditional 5.0 pushrod engine. Stock (but freshly tuned) 5.0s typically spin the Dynojet rollers to the tune of 180-190 hp. That means the '99 4.6 is significantly stronger out of the box than our beloved 5.0.
But, of course, we all know the difference. The 5.0 responds incredibly well to even the simplest bolt-ons, and makes big power with only slightly more complicated parts, like cylinder heads and a hotter camshaft. Three hundred rear-wheel hp is not too difficult to achieve with the right combination of parts, all without ever having to pull the short-block off its mounts. When trying to hot rod the 4.6, however, we've often ended up beating our heads against the wall due to the lack of high-performance parts available, the expense involved with those parts that do exist, and the ominous OBD-II computer nightmare. Our '96 GT project car has so far received most of the parts we can throw at it, including SVO heads and intake, exhaust, 4.10 gears, and nitrous. Without the nitrous, it's making 240 horses at the wheels.
That's why we're enthusiastic about the newly revamped '99. The body style seems to be a love-it or hate-it deal, but the engine is another story. The heads on the '99 are vastly improved over the previous design. While they're not the exact same SVO heads we're now familiar with, they're very close, using essentially the same port and combustion chamber layouts. The other improvements involve a slight change in the intake manifold, a new fuel system, and some revised computer calibration. As soon as the new cars started hitting the streets, we began to hear from shop owners telling us how much power they were making, and nearly all were getting over 230 hp on a Dynojet.
Okay, fine, the '99 is greatly improved over the previous years. But will it respond to traditional bolt-ons? Aftermarket heads are out of the question (for now), since the SVO heads are basically already there, and nobody else makes 4.6 heads. But what about the easy stuff, like pulleys, a K&N, better exhaust, and a bigger mass air sensor? We wanted to find out, so we put in a call to Steeda, who just happened to have a few of them in the shop.
Our testing guinea pig was a white '99 GT five-speed provided by local dealer Sawgrass Ford. We dyno'd the car in stock, as-delivered trim, then started in with the bolt-ons. In order, they were a K&N air filter, Flowmaster three-chamber mufflers, underdrive pulleys, 77mm mass air meter, 70mm throttle body, and Steeda computer chip. When we were finished, the car responded with a gain of 23 hp and just under 19 lb-ft of torque.
When all was said and done, the white 'Stang was putting 253 hp and 293 lb-ft to the rear tires. That's impressive for roughly $1,000 worth of bolt-ons, but we haven't told you the best part. On the very same dyno, a stock '96-'98 DOHC Cobra-what most people consider the only real choice for late-model Mustang performance-makes 260 to 265 hp at the wheels. That's right-for just over a grand in bolt-ons and an afternoon's time, you can make a '99 GT run with a '98 Cobra. Kinda makes you look at the new Mustang in a different light, doesn't it?