‘ The true nature of the XK is to be an object of desire, and to turn the cars it powered into ever more desirable machines’
‘ The true nature of the XK is to be an object of desire, and to turn the cars it powered into ever more desirable machines’
‘ On our 3.4 Goodwood-spec engine, we’ re running a very shallow piston and a much longer conrod to get the stroke longer. There are lots of things you can do internally to get better torque out of them. We have had a play at doing a 5-litre XK engine, which is just an absolute battle bus bruiser. But what we have found out is that a 4.7-litre is actually better. It’ s just a nicer engine. We’ ve hit all the limitations when it comes to big litre-age compared to revs, compared to vibration. We’ re building a 4.7 twin-spark XK engine going into a 1953 Mark VII, which should be about 340hp, which is just silly.’
If there’ s a sweet spot for race engines, what does William think is the best combination of XK capacities and carbs for the road?‘ Arguably the best engine out of all of them is a 1968 4.2, which is probably the most refined and the smoothest. It’ s the most GT specification engine. I think the best XK engine is probably the 3.4 that you got in the Mk I Jaguar. Everything from 3.4 onwards was chasing a financial number. The 3.4 was the first draft, the first attempt, probably with the best minds involved on it.
‘ On triple HG8 SUs, too. I’ m not actually a fan of Webbers for road cars. They’ re awesome for the pedal-to-the-metal flat-out grunt, but driving them, I just don’ t see the benefit from a power output. You can’ t idle, you can’ t blip very easily and you’ ve got a terrible tendency to bore wash them if you don’ t drive them properly. I think a 3.4 with all of the Haynes refinement on it, I think it’ s the one to go for.’
The truly difficult question now: how much does a rebuilt engine from William Heynes Ltd. cost?‘ If you get a completely standard engine, using completely standard conrods and a completely original crank, it comes in between £ 15,000 and £ 20,000. If we’ re into new cranks, new conrods, new cams, that’ s probably pushing £ 30,000. So I think an average engine from WH probably comes in at about £ 24,000.
‘ I really do think it’ s a bargain because people are charging double that for less work. But the machining cost has gone from £ 5000 when I first started up to £ 11,000 in less than five years. And that’ s the reason for the expense; it is down to the quality of the machining.’
The true nature of the XK, to be an object of desire, and to
turn the cars it powered into ever more desirable machines, is being kept alive by William. The spirit of using cutting-edge technology where appropriate and an exacting attention to detail is clearly a similar engineering approach taken by his grandfather. Understanding the XK’ s origins, its current reputation and its beauty have highlighted one egregious error, however, all of those picturesque stereotypically British watercolour birthday cards sporting Jaguars missed a major element. Yes, the bodies of the cars are pretty, but to really show the best of Britain, we should have been able to see the XK engine too.
From racing to crossing continents, the Jaguar XK straight-six is still ideal for many tasks
32 The Engine Rebuilder Issue 06