Technology that allows an engine to switch between Otto and Atkinson cycles is featured in the updated 467-horsepower 5.0-liter V8 that powers the 2015 Lexus RC F. The 2UR-GSE engine runs on the Atkinson cycle when operating at cruising speeds. That is, the intake valves are held open longer than normal, creating a reverse flow of air into the intake manifold. This action decreases the pumping loss, or reduces the effort the piston needs to cycle through the compression stroke, and also increases the thermal efficiency of the engine. When more power is required, the engine switches over to the Otto cycle. Compression ratio is 12.3:1.

EngineLabs went into more detail about this operation in a profile of the Lexus 2.0-liter turbo engine. Key to the cycle switches is a redesigned variable-valve-timing system that uses an electric motor to extend the range of operation for both performance and fuel economy.

The updated 5.0-liter is based on the engine found in the IS F but now has 51 more horsepower and the rev limit jumps to 7,100 rpm. Basically, the block carried over with just about all other internals specific to the RC F engine. For example, the crankshaft now has smaller counterweights and reduced bearing sizes. Also new are titanium intake and exhaust valves, forged connecting rods and dual-injection system with a 2,611-psi fuel-rail pressure. Other new features include 4-2-1 exhaust headers, 10-percent larger throttle body and revised camshaft profile. Breathing was improved with reshaped cylinder-head ports, and lubrication was upgraded with a modified oil-pan baffle and new air-to-oil cooler.

Backing up the 5.0-liter V8 is an 8-speed transmission with four different shift modes, and there’s an available electronically controlled torque-vectoring differential that can adjust the multi-plate clutches every one-thousandth of a second, regardless of engine torque.