11/1/2007 | 4 MINUTE READ

Risk and Reward

A performance sub-brand wasn’t part of the Lexus plan, but that was before one man convinced management to let him create the IS F.
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Yukihiko Yaguchi, the chief engineer for the IS F, followed an indirect path to creation of this car.


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Yukihiko Yaguchi, the chief engineer for the IS F, followed an indirect path to creation of this car. A 30-year Toyota veteran who joined the company straight out of school, his first assignment was noise, vibration, and harshness reduction on the domestic market Toyota Crown. From there he moved to the development teams for the first two generations of the Lexus LS, the Toyota Supra, and the Lexus GS. Throughout, he dreamed of building a car that was both fast and fun-to-drive. “That car didn’t have to be a Lexus, it could have been a Toyota,” he says, “but it had to be a rival for BMW’s M3.” It would take nearly four years for Yaguchi to get Lexus Product Planning’s approval to expand his engineering and development team and produce a proof-of-concept vehicle—a first generation Lexus IS fitted with a Toyota Racing Development 5.2-liter V8—his team built after normal working hours. Approval didn’t mean the floodgates were open, however. Rather than the typical engineering and development team of 1,000-1,500, Yaguchi had just 100-300 members at any one time—but they were hand-picked.

That number included the staffs from Toyota Technocraft and Yamaha that were assigned to the project. It was the first time in its 53-year history that Toyota Technocraft—better known for its work building police packages and aero kits for Toyota cars—worked on a production project. And Yamaha, known for its long history of engine development for Toyota, provided help through its aftermarket division, a group run by the former head of its Formula One engine program Yaguchi friend Takaaki Kimura. “I much prefer having a small, focused group,” Yaguchi says. “Not only is it more satisfying, decisions can be made and implemented quicker.”

That didn’t mean the car appeared overnight. Development spread over 4.5 years and ran slightly behind, but parallel to, the mainstream IS program. Unlike the first IS, the latest generation has an engine compartment sized to accept a V8, thanks to the platform it shares with the GS sedan. Developed from the UR engine family, the V8’s block has the same 94.0 mm x 89.5 mm bore and stroke, and is topped by Yamaha-designed and built aluminum cylinder heads with more vertical ports for better breathing. Both direct and port fuel injection are used to enhance efficiency and give a fatter torque curve. The titanium intake valves use rocker arm-activated solid lifters, and are fitted with electric motor-actuated variable valve timing. [Variable timing on the exhaust side is hydraulically controlled.] To make certain the heads are not starved of lubrication under high loads, a head scavenge oil pump is fitted. The throttle valve shaft is notched to increase airflow and reduce intake resistance. Primary and secondary inlets feed air to the engine, with the secondary port opening at 3,600 rpm. This changes the engine note significantly, and underscores the engine’s 416 hp @ 6,600 rpm, 371 lb-ft @ 5,200 rpm, and stout 11.8:1 compression ratio. The 4.0-liter V8 in BMW’s latest M3 sedan, by comparison, produces 414 hp @ 8,300 rpm, 295 lb-ft @ 3,900 rpm, and has an even higher 12.0:1 compression ratio.

Unlike M3, the IS F does not offer a manual transmission. However, the AA80E eight-speed gearbox is up to the task with its four clutches, twin disc brakes, a single one-way clutch, a lock-up torque converter that operates in all but first gear, low first and second gears, closely spaced third through eighth gears, and an electro-hydraulic control system. The latter can simultaneously engage and release clutches for more seamless upshifts through the use of high-pressure linear solenoids. Shift initiation takes 0.2-seconds, while gear changes are performed in half that time. The gearbox is controlled through the console-mounted shift lever or through steering wheel-mounted paddle shifters, and has a breather system that releases internal air pressure while preventing fluid loss.

The F’s suspension is similar to that of everyday IS sedans with a multi-link/dual A-arm setup in front, and a full multi-link independent rear. However, the upper and lower A-arms are made of high-strength sheet steel, forged aluminum steering knuckles reduce unsprung mass, spring rates are up 90%, and the hub bearing units are stronger. In back, optimized toe control links are fitted, the spring and damper rates are up 50%, and—like the front—anti-roll bar rates are increased. Forged 19-in. BBS wheels are employed front and rear, are 40% lighter than cast aluminum wheels of the same size, and cost about 3.5 times more. Brembo drilled rotors—14.2-in. x 1.2-in.—with pillar cooling fins and six-piston monobloc aluminum calipers sit up front, while a similar disc design [13.6-in. x 1.1-in.] with two-piston monobloc aluminum calipers provide retardation at the rear.

Yaguchi states his goal was to create a car that, “was fun to drive under all conditions and for all driver skill levels,” which meant altering the standard integrated vehicle dynamic control—throttle, power steering effort, shift points, ABS, brake assist, traction control, brake force distribution—to provide more than lowest common denominator intervention. Thus, the system extends the linear and lateral g limits, increases throttle response and shift points, and enhances steering weight in Sport mode. It cuts traction and vehicle stability control without affecting ABS or the electronically controlled brake limited slip system when switched off.

In creating a high-performance sedan for the normally staid Lexus line, the IS F chief engineer and his team also forced the creation of a sub-brand that was not part of the original planning. When asked about this Yaguchi says, “There were some who thought I was nuts, and—undoubtedly—some still do, but the bigger risk would have been in not building this car.”