Editing Jaguar V12 engine (section)

==Development==
Initial designs for a V12 engine were produced by engineer Claude Bailey as early as 1951, with a view to using it in a [[24 hours of Le Mans|Le{{nbsp}}Mans]] race-car.<ref>Daniels, Jeff. ''Jaguar — The Engineering Story'', Haynes, 2004. {{ISBN|1-84425-030-X}}</ref><ref>{{cite web |url-status=live |url=https://buildingthelegend.co.uk/the-jaguar-v12-part-one-origins |archive-url=https://web.archive.org/web/20240202075624/https://buildingthelegend.co.uk/the-jaguar-v12-part-one-origins |archive-date=2024-02-02 |title=Jaguar XJ13 - Building the Legend |access-date=2024-02-02 |df=dmy-all }}</ref> Bailey's original 8.0 L design used [[double overhead camshaft]]s heads sharing the same basic layout as the [[inline 6|inline 6-cylinder]] [[Jaguar XK engine|XK engine]], in order to allow for a relatively high [[redline]].<ref name=jagweb1>{{cite web|url=http://www.jagweb.com/aj6eng/v12-engine/page1.php |title=The technical history of the Jaguar V12 engine|publisher=AJ6 Engineering |access-date=2013-06-20}}</ref> Even after Jaguar withdrew from racing in 1957, the V12 design continued to be refined, and Bailey proposed a range of displacements from 7.6 L (sharing 87 mm bore and 106 mm stroke measurements with the 3.8 L XK) down to 5.0 L (sharing the 2.4 L XK's 83 mm bore and 76.5 mm stroke). In 1962 Bailey was instructed to begin prototype tooling and bench testing of a 5.0 L design, having settled on an 87 mm bore and 70 mm stroke.

By 1964 several incarnations of the V12 engine were being tested, including versions meant for racing and others for installation into production cars. An all-aluminium quad-cam design with fuel injection was created for the XJ13, while cast iron blocks and heads, and other double and single overhead cam head designs were created for use in a production road car version. These production versions of the engine were tested in [[Jaguar Mark X|Mark X]] saloons.

After the XJ13 project was cancelled the team of Hassan and Mundy designed a new single overhead cam head, with the camshaft lobes acting directly on vertically-inclined valves through bucket tappets. This was similar to the cylinder head design of the contemporary [[Rover P6|Rover 2000]], with which the Jaguar V12 also shared the use of dished [[Heron cylinder head|'Heron']] pistons. These changes reduced complexity, weight, size and noise, and were anticipated to help the engine meet future emissions standards.<ref>{{cite web|url=https://www.youtube.com/watch?v=pPxpPYLW4kw |title=Jaguar V12 explained by Walter Hassan and Harry Mundy|website=[[YouTube]] |access-date=2013-06-20}}{{cbignore}}{{Dead Youtube links|date=February 2022}}</ref>

The revised head design by Hassan and Mundy also had longer, more restrictive inlet ports sacrificing top-end power but which—along with an increase in displacement to {{convert|5344|cc|L|1|order=flip}} (90 mm bore x 70 mm stroke)—greatly improved performance at lower and mid-range engine speeds, which was more desirable in heavier luxury cars. The chain-driven SOHC heads and the softer valve springs fitted to reduce valve train noise resulted in the red line being lowered to 6,500&nbsp;rpm from the 8,000&nbsp;rpm of the original DOHC design. The engine was continuously refined with various carburettor and fuel injection arrangements before finally seeing production in the Series III E-Type in 1971.