We don't care what Ford rates it at. Bottom line is this sumbitch is one strong workhorse, obviously the most powerful mill Ford's ever seen fit to stuff into a Mustang. We can only imagine what it'll do with a pulley swap, air intake upgrade, and computer tune. We're guessing 600 rwhp is not out of the realm of possibility with these tweaks.
As it did with the legendary Terminator engines, the Special Vehicle Team stuffed the 5.4 block with all the necessary hardware to keep it alive under the most rigorous duty--a forged steel crank, forged aluminum pistons, and cracked forged steel I-beam connecting rods. Compression checks in at a blower-friendly 8.4:1, and the redline is set at 6,250.
Like the GT, it's got 2.5-inch exhaust from the cast-iron manifolds to the tailpipes. Unlike said Mustang, however, it is not equipped with an H-pipe. For the first time in a Ford vehicle, the Shelby employs an X-shaped crossover. This smoothes out the sound quite a bit. From the inside, it is quieter than a stock 4.6 Three-Valve, but we're told it is pretty much as loud as legally possible under full throttle. The X also added 10 hp to the mix. Thankfully, the air hiss that was present under full throttle in '03-'04 Cobras (which one engineer said "sounded like a '78 LTD") is gone.
For a gearbox, SVT chose the latest, smoothest version of Tremec's six-speed, now dubbed the TR6060. The ratios are similar to the earlier version, but first is a lower 2.97:1 (versus 2.66). There's a usable 0.80 Fifth, and a 0.63 Sixth for fuel economy. With the mountains of torque available, Ford elected to use a highway-friendly 3.31:1 final drive (with an upgraded diff). This helped keep the GT500 from being slapped with a gas-guzzler tax; hot rodders will immediately want to switch to 4.10s or 4.30s.
No more IRS, Ford tested this...
No more IRS, Ford tested this solid rearend to 500 high rpm launches with no failure.
Fans of automatic transmissions are out of luck since Ford doesn't make one that can cope with this car's power.
Obviously, we've made no mention of an independent rear suspension since, well, there isn't one. While this will send some lapsing into spasms, we've seen enough grenaded IRS units from previous SVT Mustangs (not to mention new Pontiac GTOs) that we are grateful for the omission, if you can call it that. So there's a tradeoff--a little more brake dive and a little movement in back if you hit a bump or two in a corner versus a more efficient driveline that puts more power to the ground, is lighter, and is virtually indestructible (not to mention cheaper to produce). Not only has the new three-link proven itself on the track in Grand Am cup, where it has kicked Porsche and BMW ass, but in Ford's testing it withstood 500 high-rpm drag launches without failure.