The most obvious external difference in the car since we last featured it is the slicks an
The SVO intake and Vortech S-Trim are obvious additions. Not so clear is what has been don
Steedas potent powerplant retains the block and remains at 4.6L of displacement, but
To handle the rpm levels and blower boost, a forged Cobra crank (right) was used in place
A quick wheel/tire change and the car regains its road race appearance. These Nitto drag r
Wiseco whittled out the dished blower pistons (left, compared to stock pistons, right). Th
Manley steel rods (left) are considerably stronger than the stock rods.
Unless you're new to the 5.0 world, this car is a familiar sight. Steeda let us wring the wee out of this '97 GT back in the Oct. '97 issue, in which it graced the centerspread and cover. Though it looks like the same car, since our first experience with it, the GT has undergone a complete transformation under the skin. Back then, it ran 13.60s with a Vortech-supercharged 4.6. It's much faster now.
Nearly all of the aftermarket mod-motor development work has centered around the DOHC 4.6 Cobra motor. With the exception of Ford SVO, nobody's paying any real attention to the two-valver in the way of speed parts. There are actually more parts available for the two-valve engine (thanks to SVO), but the aftermarket hasn't capitalized on them, instead attempting to sap as much power from "the real motor," the Cobra. Steeda's Dario Orlando realized that there are many more two-valve Mustangs running around than Cobras, and that the market has to be there for hot two-valve cars. So he decided to push the envelope in an attempt to create a brutally fast, marketable GT. And the red car was a natural.
When we last tested this car, it had a stock 4.6 long-block with a free-flowing exhaust, and a Vortech blower providing lots of boost. The car was relatively quick, especially considering it wasn't a Cobra, but Steeda wanted it to be quicker. And, Steeda's in the business of selling parts as well as turn-key cars, so it was only natural to turn up the wick a little and see what would happen. That involves using everything Ford SVO has available for the 4.6--in addition to some good old hot rodding techniques inside the engine.
The key components to power are the SVO cylinder heads, intake manifold, headers, and throttle body, which are topped by a Vortech blower. Initially, the blower would be set at a streetable 8 to 10 pounds, but Steeda wanted to eventually get nutty with the boost and make some real power, so the bottom-end of the engine got plenty of attention. The weak link in the SOHC 4.6 bottom-end was... well... pretty much everything except the block. The stock cast crank was replaced with a beefier Cobra forged crank; the rods gave way to Manley steel rods; Wiseco pistons (with stock-type offset pins) replaced the stock hypereutectic slugs.
Steeda stayed with the GT's iron block, as opposed to using an aluminum Cobra block, for two basic reasons. For one, an iron block is stronger. An aluminum block is great for weight savings and the romance factor, but under extreme cylinder pressures (as with lots of boost or nitrous) the aluminum block can walk around--meaning the cylinder bores and main bearing journals can move.
That's not good for power or durability. The second reason is price. An aluminum block is mucho-expensive. You may be wondering why cost is such a concern if they're willing to use all the other trick parts. The answer is that these parts aren't that trick--they're all off-the-shelf parts. Custom stuff is what's expensive, and the Cobra crank only costs around $550 from Ford. Since the eventual intent was to crank the boost up to 18 pounds or more, the compression ratio was kept to a conservative 9:1. The SVO cylinder heads and intake were installed as-delivered, with no additional porting.
If you're not familiar with these heads, they have higher-flowing ports, bigger valves, and unshrouded intake valves. SVO claims the intake ports flow 27 percent more than stock heads, and the exhausts are a respectable 44 percent better than stock. The intake also was completely redesigned to increase top-end power without taking it away down low. A Cobra twin-bore (57mm each) throttle body and Pro-M 77mm mass air meter mate to the intake, and 30-lb/hr injectors do the squirtin'. The other engine changes included a Motorsport vibration damper, a Cobra flywheel (the flywheel flange bolt pattern is different between the SOHC and DOHC cranks), an SVO windage tray, and an SVO high-volume oil pump kit. The camshafts are stock, and Steeda feels they work well with the combination.
With just over 10 pounds of boost from an S-Trim Vortech, the combination was good for an astounding 460 hp at 6,000 rpm and 418 lb-ft of torque at 4,600 rpm, at the rear wheels, on Steeda's Dynojet. Running at the Spring Break Shootout in Bradenton early in 1998, this combination was good for 11.89 at 115 on slicks, and 12.30 at 113 on Nitto drag radials. A gutted race car this ain't. With the driver, you're looking at a 3,700-pound, off-the-showroom-floor, loaded GT.
Like we said, the reason for building a bulletproof bottom-end was to enable cranking up the boost, but the dyno and drag testing has uncovered the first weak link in the combination you see here--fuel delivery. The stock fuel system is only good for about 450 rear-wheel horsepower. After that, the fuel rails and pump are overtaxed, especially with 30-pound injectors. More boost would create a lean condition and start burning up stuff. Steeda is developing a complete fuel system, including new fuel rails, to allow 500 hp and beyond.
Naturally, development of this package is a continuous affair. In addition to the new fuel system, the engine will get a new pair of Crane cams, and Steeda's working on a new aluminum discharge tube for the blower, to prevent the nagging problem of it blowing off at high speed. For now, the heads and intake won't be ported because Steeda wants to see how much power can be made with true bolt-on parts. Steeda's goals with this car are as much for its own education as they are to offer complete packages. When a customer calls and asks how to make 400 hp with a 4.6 GT (or 450, 500, or more), Steeda can tell 'em exactly how to do it and sell 'em the parts to make it a reality.
And to think, people still think the SOHC mod-motor is a pig. Don't tell Dario Orlando that, or he'll blow your Cobra's doors clean off.