You can make your GT run like...
You can make your GT run like Bob Cosby's Cobra by swapping in a Four-Valve engine from Mustang Parts Specialties. Tim Matherly and the crew from MV Performance made the swap look as easy as taking candy from a baby. Of course, the only ones crying will be the drivers in the other lane once their doors have been blown off with your newfound power.
The secondary throttle plates (Intake Manifold Runner Controls) found on '96-'98 Four-Valve engines were designed to give the Cobra the best of both worlds-excellent low-end torque and top-end horsepower. The rectangular port was responsible for the low end, but at 3,200 rpm the throttle plate would open, allowing the round ports to take over and provide the top-end kick for which Four-Valve engines are known.
Of the swaps we feature in this issue, a Two-Valve to Four-Valve may just be the easiest to pull off. During the swap process, we repeatedly asked MV Performance's Tim Matherly, "Well, do you have to change this?" His answers kept coming back, "Nope!" However, even though it may be the easiest swap to do, it's far from the least expensive, with the initial engine investment the most difficult to swallow.
The first order of business...
The first order of business will be to evict the Two-Valve from its living quarters. There are a couple different ways to make this happen. The engine and transmission can be removed as a single unit, or to make it a littler easier, you can disconnect the two. You'll also need to disconnect the wiring harness and fuel lines before the engine can be removed.
We chose Mustang Parts Specialties as the engine supplier since it's only a stone's throw from MV Performance's Statham, Georgia, headquarters. The company has Four-Valve engines from $2,900 that have been removed from '96-up Cobras. Obviously, the newer the engine, the more expensive it will be. A '99 Four-Valve will set you back roughly $4,750. These engines don't have the front accessories on them, but except for the alternator, the Two-Valve and Four-Valve share the same accessory design and components. For this swap, a corresponding computer and wiring harness will be necessary. Thankfully, MPS has these items on the shelf as well.
Before you go into shock from realizing how much this swap will cost, check out the prices for built Four-Valve engines from various Mustang shops. It can get expensive, but if ultimate modular horsepower is your goal, a Four-Valve Cobra engine is the best way to begin.
As there are few parts needed to complete this swap, we will give an overview covering the ones you don't need to change. Follow along as we show you how to inject your GT with Cobra venom.
With the two engines side...
With the two engines side by side, you can tell right away the Four-Valve is wider than the Two-Valve. But since the GT and the Cobra share the same engine compartment, the Four-Valve will have no problems fitting like a glove. You have to admit the Cobra engine looks much more menacing than the GT's Two-Valve, at least without a Bullitt intake on it.
Since the two engines share...
Since the two engines share the same mounts and K-member, the Four-Valve Cobra engine can be installed in place of the Two-Valve with relative ease. Swap out the computers and engine wiring harnesses and you're well on your way to enjoying the benefits of Cobra power.
Since each 4.6 engine differs...
Since each 4.6 engine differs little from any other 4.6 modular (except for the Cobra having a steel crank), the Four-Valve Cobra's power advantage obviously comes from the improved breathing capabilities of the Four-Valve head design. The '99-up Cobra's tumble-port heads flow less than the '96-'98 twin-port design, but they have shown to be more than up to the task of making awesome power. Notice how the earlier heads have different-sized intake passages, while the '99-up has a single oval-port configuration. The earlier heads use the rectangular port up to around 3,200 rpm, then the Intake Manifold Runner Controls open to allow the round port to do the work. The '99-up heads do not have this feature, but there are likely few '96-'98 Cobras still using the IMRCs.
You won't have to swap to...
You won't have to swap to a different clutch. The only change you need to make here is the flywheel. The Four-Valve Cobra engine uses an eight-bolt flywheel as opposed to the Two-Valve's six-bolt flywheel. You can either get a flywheel with the engine and have it resurfaced or get a trick, lightweight unit such as this McLeod flywheel we featured in the Jan. '02 issue ("Drivetrain Diet," p. 61).
In case you were wondering...
In case you were wondering why swapping in a Four-Valve Cobra engine is beneficial, take a look at the "DaSilva Edition" 2000 GT featured in the Feb. '02 issue ("Street at Joe's," p. 58). Joe DaSilva's 2000 GT features a nonintercooled Vortech SQ V-2 supercharger, a full MAC exhaust including long-tube headers, MAC underdrive pulleys, a 70mm throttle body, 30-lb/hr injectors, and a Pro-M 83mm mass air meter. The GT pounds out 356 hp and 342 lb-ft of torque.
Since many shops have gotten...
Since many shops have gotten into modifying the '96-'98 Four-Valve intakes by deburring, porting, and polishing, the same can be said of the '99-ups Four-Valve intake. These improvements have shown great horsepower potential, especially in blown applications.
Even though the '99-up Cobra...
Even though the '99-up Cobra and GT T45 transmissions are different, if your GT already has a T45 in it, you don't need to swap anything. The difference between the two is the tailshaft. The mounting spot for the Cobra is farther back on the Cobra's tailshaft when compared to the GT's. The Cobra's transmission mount is somewhat adjustable, whereas the GT's mount is fixed. Since we were using a '99-up GT for this swap, we didn't have to worry about any speedometer issues as the '96-up Mustangs all use an electronic speedometer.
In contrast, take a look at...
In contrast, take a look at the dyno numbers of Dianna Sullivan's '98 Cobra, which was featured in the Apr. '02 issue ("Beauty and the Beast," p. 82). Remember that Joe's is a 2000 GT rated at 260 hp at the flywheel from Ford, while Dianna's is a '98 Cobra, which was rated at 305 hp from the factory. Dianna's Cobra boasts just a Vortech S-Trim, a Pro-M 77mm mass air meter, a Bassani X-pipe, and a Vortech T-Rex fuel pump. With just these additions, Dianna's Cobra spanks the rollers to the tune of 426 hp and 360 lb-ft of torque. That's a 70hp difference between the two. There's so much horsepower potential available with a Four-Valve, it's not even funny.
This looks fun, doesn't it?...
This looks fun, doesn't it? Would you really want to go through this swap and not add a blower? We didn't think so. If this picture doesn't get your blood going, put down the magazine and check to see if you have a pulse.