The letter F is an auspicious one in Lexus lore. Back in the mid-'80s, when the Lexus brand was still in the planning stages, Toyota insiders referred to the prospective luxury division as "Circle F." And the car that put Lexus on the map, the LS 400, was known internally as Flagship One, or F1. For 2008, the letter F is back: The company has decided to crash the über-sport sedan party with the 2008 Lexus IS-F, a hard-edged performance car based on the IS-series sedan and aimed squarely at perennial magazine-cover fodder like the Audi RS4, BMW M3 and Mercedes-Benz C63 AMG.

The IS-F marks the official launch of Lexus' F line, and it's akin to the aforementioned competitors' in-house performance divisions. As such, Lexus has gone to great lengths to differentiate the IS-F from its more sedate IS-series brethren. Take the IS-F's exclusive power plant, for example, which begins life as the gas-swilling half of the LS 600h L's hybrid engine and then gets a thorough makeover from Toyota's longtime performance partner, Yamaha. The end result is a 5.0-liter V8 that churns out 416 horsepower and 371 pound-feet of torque, compared with 306 and 277, respectively, from the IS 350's already potent 3.5-liter V6. Likewise, the IS-F eschews the IS 350's six-speed automatic transmission for a heavily modified version of the LS 460's eight-speed unit that boasts Ferrari-quick upshifts and automatic throttle blips on downshifts. The singularity and complexity of this powertrain serve notice to the old guard that this Lexus means business. Like its F1-cum-LS 400 forebear, the 2008 Lexus IS-F is designed to go toe to toe with the best.

Outside the engine room, however, the IS-F has a few kinks to work out. For one thing, while its extensively revised suspension is dynamite on the track, the IS-F falls well short of the ride-handling balance for which certain rivals are justly famous. For another, its exterior styling cues range from the controversial (e.g., the reshaped hood and snout required to accommodate the 5.0-liter mill) to the downright tacky (e.g., the quad-stacked tailpipes that aren't actually connected to the exhaust system). Its German competition, on the other hand -- as well as the upcoming Cadillac CTS-V -- feature relatively compliant rides and subtle aesthetics.

There's no doubt that the IS-F is a serious driver's car, but we can't help but wonder whether its hardcore personality is a little over the top for this segment, notwithstanding its commendably hushed interior and rather incongruous lack of a manual transmission option. Enthusiasts with 60 large to plunk down on a sport sedan may find the IS-F a smidge too fast and furious for their tastes.

Nonetheless, the 2008 Lexus IS-F is a thrilling car on its own merits, and its uncompromising nature indicates that Lexus is willing to do what it takes to ensure that its sporting F models will be competitive with class leaders. The company has already hit two home runs with the letter F, and while it hasn't quite knocked the IS-F out of the park, it's still a promising first step toward challenging the established heavyweights for the factory performance crown.

The 2008 Lexus IS-F is a high-performance version of the Lexus IS-series sport sedan. Only one trim level is available. Standard features include 19-inch alloy wheels with high-performance tires, Brembo brakes, xenon headlights, heated and leather-trimmed 10-way power-adjustable front sport seats, driver and front passenger memory settings, dual-zone automatic climate control, a 13-speaker audio system with six-CD changer and auxiliary audio jack, keyless ignition/entry and a moonroof.

Among the available options are adaptive cruise control, a 14-speaker Mark Levinson CD/DVD surround-sound audio system, satellite radio, iPod integration, park assist and a DVD navigation system with back-up camera and Bluetooth capability.

The 2008 Lexus IS-F is powered by a 5.0-liter V8 engine that generates 416 hp and 371 lb-ft of torque. An eight-speed automatic transmission routes the V8's prodigious thrust to the rear wheels. Although the automatic is the only available transmission, Lexus says it rivals the performance of the best automated-clutch manuals, with 100-millisecond upshifts and automatic rev-matching on downshifts.

In our instrumented testing, the 3,780-pound IS-F sprinted to 60 in 4.8 seconds en route to a 13.2-second quarter-mile at 109 mph -- impressive numbers, no doubt, but a tad underwhelming given that we've clocked an IS 350 at 5.2 seconds to 60 and 13.8 seconds at 101.2 mph in the quarter-mile. Don't get us wrong -- the IS-F flat-out hauls. The Germans, however, remain a few ticks faster on the stopwatch.

Stability control, traction control, antilock brakes with brake assist, front-seat knee and side airbags and full-length head curtain airbags all come standard on the 2008 Lexus IS-F. An optional pre-collision system employs radar to monitor the likelihood of a frontal collision and adjusts seatbelt tension and braking force accordingly.

The IS-F has not been officially crash tested, nor is it likely to be. However, in government crash tests, its IS 350 sibling earned four stars (out of a possible five) for driver and front-passenger frontal impact protection. It also earned five stars for front side impacts and four stars for rear side impacts. The Insurance Institute for Highway Safety gave the IS 350 its top rating of "Good" after administering frontal-offset and side-impact crash tests.

Cars in this class are all about the experience behind the wheel, and the 2008 Lexus IS-F mostly impresses. The new V8 emits a spine-tingling roar at full throttle once you've cleared 3,600 rpm, and the engine proves eminently tractable throughout its linear power band. While the IS-F's electric steering rack is somewhat short on feel, it holds a line tenaciously in hard cornering, and grip from the substantial rubber is first-rate. Stopping distances are similarly impressive thanks to the car's massive Brembo brakes.

Turn off the stability control system and the IS-F will do powerslides all day if you've got tires to spare. What's more, the eight-speed automatic actually performs as advertised: We can't believe how well it emulates the behavior of a genuine automated-clutch manual transmission. We would still prefer having the option of a proper manual shifter, but the IS-F is blessed with one seriously sporting automatic.

Around town, however, eight speeds seem like two or three too many, as the IS-F is constantly hunting for the optimal gear ratio. Errand-running also reveals the secret of the IS-F's race-worthy handling: an unyielding suspension, even by the rarefied standards of this class. In other words, the IS-F feels a bit out of its element as a daily driver -- something to consider if all-out performance isn't your only priority.

Apart from some aluminum trim pieces, blue ambient lighting, the aforementioned sport seats and a two-passenger backseat as opposed to the regular IS's three-across seat (the rear seatbacks don't fold down, but there is a ski pass-through), the IS-F's interior is more or less identical to the IS 350's. That's not necessarily a bad thing, as the IS 350 features high-quality materials, excellent sound insulation and an attractive and user-friendly control layout. Unfortunately, the IS-F also inherits the cramped rear-seat legroom that's endemic to the IS-series. Prospective buyers will want to keep this in mind if they plan to ferry multiple adult-sized people around on a regular basis.