As combustion engines downsize and alternative powertrains gain market share, opportunities to work on V8s will come up less often. That’s no bad thing – it’s a measure of the progress industry is making on carbon emissions reduction.
But V8s are still cool and most engineers would love to have one on their CV. Around 400 staff at Ricardo have now, including the 80-strong core team who designed and developed the engine for McLaren Automotive’sMP4-12C carbon-fibre supercar.
The result, a dry-sump, flat plane crank unit which revs to 8,500rpm, is a clean-sheet design. Ricardo’s work began with a high-level specification, which was quickly translated into the basic engine concept.
“They knew what power and torque they wanted and from that it’s easy to get down to some metrics,” says Ricardo’s project director, Tim Yates.
“The engine has to be a certain size to produce that rating and turbocharged to be consistent with the future. Against that displacement you determine what configuration suits the product.”
A V8 is almost the default choice for applications such as this – and Ferrari’s was one of the main benchmarks – but the competition includes everything from twin-turbo flat sixes to naturally aspirated V12s.
Together with tight packaging constraints, the targets McLaren set – 600Nm/600PS, sub-200kg weight and vehicle fuel consumption resulting in emissions below 300g/km CO2 – more or less dictated the use of a V8 turbo.
A V6 turbo was considered – it would certainly have been smaller and lighter – but was ruled out, Yates says, because it would’ve meant using even higher boost pressures; those for the V8 were thought pretty high already: “Going even further would’ve meant a longer programme, or would’ve introduced more risk,” he says.
A naturally aspirated V8 was an option too, but a small displacement was not realistic. A unit of around 5 litres would’ve been too bulky: “Getting to 200kg would have been a stiffer target – that’s guaranteed,” says Yates. “And the future fuel consumption targets would’ve been very much more difficult.”
Given the weight target, all-aluminium construction was inevitable. Wet cylinder liners were chosen for durability but cast iron was too heavy. They were designed in aluminium instead, with a low-friction coating, saving 4kg.
The block itself, sand-cast by Grainger & Worrall, weighs 36kg. It’s very compact – only 201mm high – with the crankshaft centreline only 121mm from the base. These dimensions, plus the dry-sump lubrication system, keep the mass centre as low as possible, improving vehicle dynamics.
|tags:||Ricardo Oct 2011 High Performance Powertrain|