In July Porsche and Cadillac undertook at Daytona the first multiple marque LMDh test. While Cadillac was tight lipped about its V8, Porsche confirmed that its 2023 Prototype, to be called the 963, will be powered by a development of the direct injected, naturally aspirated 4.6 litre V8 from the 918 Spyder plug-in hybrid of 2013-2015.
That V8 was in turn developed from the naturally aspirated 3.4 litre V8 that powered the RS Spyder LM P2 car of 2005-2010. The MR6 was designed specifically for LM P2. It was a conventional all-aluminium alloy production and its linerless block/ upper crankcase exploited nickel silicon carbide bore coatings. The bank angle was 90 degrees and a flat plane crankshaft was employed along with a front end gear timing drive.
Four valves per cylinder were arranged with an included valve angle closer to 20 than 25 degrees serving a conventional pent roof combustion chamber. Those valves were directly operated through inverted bucket tappets by double overhead camshafts.
In developing the V8 for the 918 Spyder the bore remained 95 mm with the stroke increased from 59.9 mm (for 3397 cc) to 81 mm (for 4593 cc). The engine ran to 9200 rpm. In 2011 an RSR version was introduced, which offered 563 bhp at 10,300 rpm.
In a break with the RS Spyder the 918 had its cylinder heads reversed such that the exhaust ports faced inwards. Of this solution Porsche said, “the greatest benefit are the extremely short distances, as the hot exhaust gases are evacuated by the shortest, direct route and the exhaust gas back pressure remains low.”
This ‘hot side inside’ approach also kept the engine compartment cooler. It has been carried forward to the 963, for which Porsche has introduced turbo-supercharging.