Other than a slight offset and some beefed areas, the '05's 8.8-inch rearend is identical to the 8.8 used in '86-'04 V-8 Mustangs, so gear swaps are simple. Speedometer calibration, however, must be done through the use of a flash tuner for the computer.
Drivetrain
Orlando says the '05 GT's Tremec 3650 five-speed manual transmission is a great transmission with stout gears. There have been no issues with the '05's two-piece rear axle, which is utilized mainly for NVH (noise, vibration, harshness).
Gear swaps are the same as with previous 8.8-inch rearends. Other than some minor updates, it's the same familiar 8.8 in V-8 Mustangs since 1986. Recalibrating the speedometer for a gear change is done by reprogramming the computer with a hand-held flash tuner.
Suspension, Chassis, and Handling
From the factory, the '05 GT is the best-handling Mustang ever, with a chassis that boasts a torsional rigidity of 7,500 lb-ft, some three times stiffer than the previous SN-95 Mustang. "A stock '05 convertible is stiffer than a Fox-body Mustang with a full roll cage," points out Orlando. That certainly gives it a great platform to start with, but what can you do to make it better?
Orlando surprised us with his first recommendation. "Good performance tires. The tires that come on these cars are very tall, 235/55. You want to lower your Mustang? Go to a standard performance tire. It'll lower it an inch all the way around. We recommend 275/40x18s. That's a good profile, and we've found that it has a great ride quality as well."
Steeda's Dario Orlando says performance tires are the best modification you can make to an '05 GT for handling. He recommends replacing the factory "tall" 235/55s with 275/40s, like these Nittos, as used on the '05 Steeda Mustangs.
Because the '05 has large wheelwells, low-profile performance tires don't fill out the fenders, so lowering is the next performance option for both handling and aesthetics. But not too low. "You lower the '05 more than about 3/4-inch and you get into suspension geometry changes that are not good," Orlando says. "At the rear, you have a hydro-bushing bumpstop. Lower the car too much and the car will sit right on the hydro-bushing. At the front, the control-arm angle changes dramatically, so the roll center will migrate tremendously."
Steeda's Sport springs drop the '05 by 3/4-inch and they're designed for good riding as well as improved handling. Even better, on the '05, you can install Steeda's Sport springs without having to switch to performance struts and shocks. "The stock dampers--struts and shocks--are pretty aggressive," Orlando told us. "They're light-years better than the stock dampers on the SN-95 Mustang. Now, for the guy who is going to do open-track events, he needs to go ahead and get D-spec Tokico struts and shocks."
"For the guy who lowers his car and wants to optimize it, we recommend a relocation kit for the front control arms," continues Orlando. "Anybody can install it; the hardest part is drilling the holes, but there's so much room in the front of the car that drilling the holes in the front crossmember just takes a few minutes. It moves the control arm up in the chassis so it essentially returns to parallel, which is optimum for a McPherson strut."
Steeda spent a lot of time coming up with sway bars to complement the springs. "There's always the argument about high-rate springs and low-rate sway bars, high-rate sway bars and low-rate springs. We're kind of mid-range on that. We have springs that provide drivability and don't beat you to death. But our sway bar rates are high enough for the guy who likes to dive around the corners and embarrass a Corvette or two."
Because the '05 GT's factory struts and shocks are more aggressive than on previous Mustangs, performance springs, like these Steeda Sport versions, are effective without performance struts and shocks... | 
...although aftermarket dampers, like those from Tokico, do offer additional improvement in handling, especially for open-track events. |
To replace the '05's front springs, the struts are removed and placed in a press so the factory spring can be compressed and removed. | 
Steeda's Sport spring slides over the strut and is secured with the factory bracket and nut. The rear springs install just like previous Mustangs. The Sport springs provide a 3/4-inch lower ride height and a stiffer rate for better handling. |
The '05 Mustang chassis is three times stiffer than the previous SN-95 Mustang, so it requires fewer chassis stiffening modifications for performance handling. | 
To reduce wheel-hop during heavy acceleration, the factory rear arms should be replaced with aftermarket trailing. |
Orlando says the '05 Mustang front suspension is outstanding, but at the rear, wheel-hop can be evident when you start drag racing because of the low durometer bushings. A partial cure is to replace the factory trailing arms with billet versions with either urethane bushings, recommended for the street, or rod ends. To totally eliminate the problem, an adjustable upper link can be added. "The bushing on the differential in stock form is extremely dense, so it's pretty good. But the front bushing is a hydro-bushing, which flexes and contributes to wheel-hop. And for performance purposes, there's not enough pinion angle, especially when you lower the car. You want an adjustable link so you can change the pinion angle."
As mentioned previously, the '05 Mustang's chassis is extremely stiff, so for the street, it doesn't need the chassis-stiffening components that were almost required on Fox and SN-95 Mustangs. "It doesn't need subframe connectors," Orlando says. "The only thing we are going to offer is for guys who are putting giant slicks on the back. We will offer a triangular brace for the front mount on the lower trailing arms because there is a lot of stress there."
In this comparison of an '05 three-valve piston (left) and the previous two-valve piston, you can see the top ring land has moved up, which makes it more prone to breakage under detonation.
Weak Won't Survive
Anyone modifying an '05 GT for more performance should be aware of the engine's limits. After all, it's not Ford's responsibility to provide an engine for racing, so consequently, the three-valve 4.6 was designed for 300 hp, plus a stress safety margin. Steeda says the engine will live with 425 hp as long as timing and fuel is managed to prevent detonation. Anything more than 425 hp and "You're just waiting to buy a new engine," says Dario Orlando.
The weak links are the piston ring lands and powdered rods. For emissions, the '05 has new pistons with ring lands very close to the top of the piston. "One of the ways to control emissions is to reduce the unscavenged area around the piston," Orlando explains. "If you move the ring land up as high as possible, you have less unburnt fuel. So Ford moved the ring land up as high as they could while maintaining minimum strength. But the whole purpose of it is alien to performance because they break easily."
The powdered rods--which have been used in all modular engines except the supercharged four-valve 4.6 in '03-'04 Cobras--also have their limit. "A powdered rod is simply powdered metal compressed at extremely high pressures where it literally bonds together to make a rod," Orlando says. "And on top of that, the rod cap itself is broken off. So you take off one of the caps and it's literally jagged-edged. It's inexpensive to produce, yet it provides more than adequate strength for a stock engine. But under a performance scenario, you're really stress limited."
Through the Ford/SEMA Technology Transfer Program, Steeda has access to Ford drawings, dimensions, schematics, and more for the '05 Mustang.
SEMA/Ford Technology
Steeda's task of creating new performance parts for the '05 Mustang was made infinitely easier and more precise due to the company's participation in the Ford/SEMA Technology Transfer Program. "As part of the program," Orlando says, "we get drawings and specifications directly from Ford. Our parts are engineered to Ford specifications and guaranteed to fit the '05. Steeda already has a strong reputation for performance and quality. It's our goal to enhance that reputation."
Steeda Mustang
If you'd like to skip all the parts purchases and installations and go straight to a full-on performance Mustang, you can have Steeda build you a turn-key Steeda Q Mustang at their facility in Pompano Beach, Florida, or their satellite builder, JBA Racing in San Diego. Choosing from Steeda's extensive list, you can custom-build a Steeda Mustang from mild to wild. You can even order your '05 Mustang GT from an authorized Ford dealer and have it drop-shipped to Steeda for the conversion. Best of all, the car retains its full factory warranty. For a list of available components and authorized Ford dealers, visit www.steeda.com.