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Jaguar XKE Series 3 V-12

Jaguar XKE V-12 Horsepower

How much power did the Jaguar XKE Series 3 V-12 engine really make? A precise number is a little hard to pin down.

As finalized for the XKE Series 3, the power rating for European use was 272 horsepower on the DIN scale at 5,850 rpm. That would translate to 282 SAE. However, in U.S. marketing literature, the V-12 was said to deliver 314 horsepower at 6,200.

The signature hood buldge of the Jaguar XKE was retained in the new XKE Series 3.
The signature hood bulge of the Jaguar XKE was
retained, even though it wasn't needed to clear the
new XKE Series 3 V-12 engine.

The tachometer's redline was way up at 6,500, by the way, and the engine could actually turn to 7,840 before the valves started bouncing in their springs. Torque was listed in the same materials as 349 lbs/ft at 3,600, but the European DIN measurement was 304 at 3,800.

These differences can be explained by two factors. First, the American figures were idealized, being derived from dynamometer readings of a test engine unfettered by mufflers, air cleaner, fan, and other accessories.

Second, importers like Jaguar could easily waffle about the potency of their "American versions" because, in 1971, the switch was on from advertising the traditional, but misleading, SAE-gross measurements to more realistic net outputs, and there was some public confusion as to what the conversion factors should be.

There was also this: U.S. emissions standards were then tightening so rapidly, and even inconsistently, that stated outputs could vary a lot from one model year to the next and, sometimes, even within a model year.

This was particularly likely if a manufacturer needed to resort to different tuning to meet the stiffer emissions limits set by the smoggy state of California. We're inclined to believe 1,972 quotations in Road & Track as both plausible and definitive: 250 horsepower at 6,000 and 283 lbs/ft at 3,500, both SAE net and applicable to all 50 states.

But none of this really mattered in the end. Few Jaguar buyers have ever based their purchasing decisions on the precision of engine outputs. The important point was that the XKE Series 3 had more punch than the XKE Series 2, enough to just about bring this much-heavier, much-less-aerodynamic car back to the performance levels of the original XKE.

According to measurements made for this article of display engines at the Jaguar factory museum, the V-12 measured 2-7/8 inches longer than the old inline-six, or 35-7/8 inches from rear of flywheel to nose of crankshaft. Height was actually a quarter-inch less, 26-1/2 from sump to the tops of the induction system; the engine itself, to the tops of the cam covers, was only 22-1/4 inches high.

Of course, overall width was greater, especially when the V -12's sprawling induction system was considered. With this and all the other necessary ancillaries, the engine occupied a "box" measuring 44x39x27 inches.

So it was big -- but not especially heavy. A good deal of arrant nonsense has been perpetrated over the years about the weights of Jaguar engines. Well, they're not made of fluff and foam, but they're not boat-anchors, either.

In The Jaguar Scrapbook, marque historian Philip Porter published a list of weights of various Coventry powerplants "as installed on testbed." These were taken minus fan, air cleaner, clutch, and transmission, and without any fluids, but with flywheel, electrical equipment, and exhaust manifolds.

In this trim, a 3.4-liter XK (for the 340 sedan) weighed 567 pounds, according to Porter. The 3.8, with its added cylinder liners, came to 592, while the 4.2, which had the redesigned block with different bore spacings, scaled 605.

And the 5.3-liter V-12? A mere seven pounds heftier, at 612. With the engine dressed for installation, the factory said its total weight came to 680 pounds.

Granted, that was substantially heavier than a typical small-block Detroit V-8, but let's not forget that the Jaguar design was really a big-block enclosing a relatively small displacement -- and was an inherently much-more-complex, more highly refined design to boot.

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