Revolutionary development
High-revving naturally aspirated engines are falling from favour in mainstream applications but Toyota’s engineers wanted nothing else for the Lexus LFA supercar
- Published in Features.
A light, high-revving naturally aspirated engine was a must
Highly-efficient gasoline hybrid powertrains define Toyota’s image now. Its Prius model, which has sold in the millions, has almost become a brand in itself. Hybrids also keep the fleet-average CO2 emissions of Toyota’s Lexus luxury models surprisingly low, despite the V6 and V8s that do the work when the electric motors cannot.
But when Toyota’s engineers were developing the LFA supercar they didn’t go for a hybrid, or a downsized turbocharged engine either. What they came up with was a 4.8-litre V10 which develops its peak power of 412kW at 8,700rpm and takes the vehicle to a top speed of 325km/h.
When you want to compete with Ferrari and Lamborghini at the first attempt, you need to rely on your team’s experience of high-performance engineering. Toyota chose Takamitsu Okamoto to head the planning, design and development of the LFA’s powerplant because of his background of working on Formula One, Indy car and Group C race engines.
The result is a bespoke engine that revs to more than 9,000rpm but which is also smooth and tractable in everyday use – a prerequisite in any Lexus. The development team is pretty pleased with the results. “This is one of the most race-like production engines,” said Okamoto. “To achieve the feeling of infinite acceleration we implemented instant response, high engine revolutions and a wide torque band.
“The shut-off speed is 9,500rpm but 90% of maximum torque is achieved between 3,800 and 9,000rpm, providing driver satisfaction, and contributing to comfortable daily driving.”
Packaging was one of the main constraints, especially since the LFA has a front mid-engine layout. One of the most important measures was to minimise the cylinder bore spacing.
The crankcase is low-pressure chill-cast aluminium alloy; instead of using bulky steel liners, Toyota adopted arc spray coating. This enabled the engineers to reduce the bore pitch, so the V10 is around the same length as the V8. The coating also saved 2kg and reduced friction.
The V10 is also lower than the V8, which was essential not only for fitting it under the hood but also to improve the LFA’s ride and handling. “In pursuit of vehicle dynamic performance a low centre of gravity is essential,” said Okamoto. “The next step is to reduce the car’s moment of inertia, so we reduced the crankshaft’s centre height as much as possible by adopting a dry sump lubrication system.”
