V12 related projects



Curious to know whether more information is available on the experimental 60-degree V6 and Slant-6 engine projects apart from the former being underpowered and the latter apparently inspiring Jaguar to later develop the AJ6? At least as far as specifications and performance figures are concerned?

As for the V12 itself in retrospect how could Jaguar have improved on the engine during both development and its production run? Could the drawbacks of the proposed Quad-Cam configuration have been remedied or were there other little-known developments that could have benefited the V12 in better circumstances?

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #2

You’ll get a lot of opinions. IMHO, the V12 would have been greatly improved had Jaguar opted to go with a SOHC with rockers, the way many Honda car engines work. Utilizing rockers would have eliminated the heavy tappets and shims and would have made it far simpler to adjust the valve lash. It also would have enabled greater valve lift by utilizing rockers with a greater than 1:1 lift ratio without making the camshaft itself huge. Finally, rockers would have made it a simple matter to go with 3 or 4 valves per cylinder.

I also believe the Jaguar V12 should have grown to about 8 liter displacement as soon as the manufacturing processes permitted. It’s an atrociously heavy 5.3 and an overweight 6.0, but as an 8-liter engine it would have been reasonably fit & trim. Yeah, there was an energy crisis going on, but really displacement impacts fuel economy far less than engine mass does – and the mass was over 700 pounds anyway, might as well reap the torque benefits of larger displacement and put them to use having a big tall final drive ratio for fuel economy.

Also, obviously, I’d have recommended doing away with the 1-1/2 pass radiator scheme.


Have heard the V12 had scope for a displacement of 8-litres. Would a V12 featuring SOHC with rockers and 36-48-valves have put out more power compared to the existing V12 as well as benefited any related 60-degree V6 project?

Also wonder whether Jaguar would have been willing to opt for a SOHC V12 for what they considered a flagship engine if they were not too tied with DOHC / Quad-Cams. Know Jaguar were open to using SOHC via the Coventry Climax CFF/CFA V8 for their Baby XJ project that also featured SOHC and allegedly was capable of more then 200+ hp (assuming the 200+ hp was for the 2.5-litre CFA version though curious to know the capability of the 1.8-litre CFF version as well as whether there was scope for further enlargement),

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #4

SOHC with rockers would definitely have resulted in more power resulting from increased lift and perhaps more optimal valve location, as the valves would no longer have to line up under the cam. 36-48 valves would have apparently resulted in more power, judging from the experience of other manufacturers, even though one big hole generally flows better than two little holes. One need only observe the experience of Ford with their Modular engine as it has evolved into today’s Coyote, now producing 460 HP from 5.0 liters.

But perhaps that isn’t the correct question. These developments add power, but they typically also add weight, complexity, and even physical size to the powerplant. Jaguar opted not to move forward with a DOHC layout because the weight and size of the heads were prohibitive. Again, to point to experience with other manufacturers, Chevy has opted to compete with Ford’s Coyote engine without going to overhead cams or more than two valves per cylinder. Their LT1 engine likewise produces 460 HP; it’s no accident it’s exactly the same number. Instead of going with the fancy valvetrain, Chevy simply goes with more displacement: 6.2 liters. And despite the engine being “larger”, car guys report that the LT1 will fit in any hole the Coyote will fit, it weighs less, and it costs less. A simple visual comparison shows that the Coyote has great big, massive heads on it compared to the LT1’s simple rocker covers.

Thing is, though, that Jaguar had limited resources for development in those days. They basically had to choose a layout based on their best guess and run with it. They didn’t have the option of building multiple prototypes and seeing which ones worked best.

(ronbros) #5

Kirby is correct, Jaguar should have used a good old American V8, after all they used GM transmissions, and Dana USA differetintals, P/S pumps,ETC. GM has produced an LS V12 all aluminum engine!

and saved a ton of money, on development costs(as always its all about the money).

today its easy to look back and see the short comings, but complicated engine designs take years to get reliable!



My bad. Was thinking of terms of Jaguar possibly perceiving SOHC on the V12 as a step backwards as a result of the XK6 engine being a Twin-Cam design.

What would have been the best approach to take in developing a V8 that would related to some degree with the V12 instead features a 90-degree layout in place of the 60-degree layout originally investigated? That is apart from Henry Spurrier living long enough to give William Lyon’s favorable terms to join Leyland Motors.

Would SOHC with rockers have benefited any related 60-degree V6 or Slant-6 projects and prevented them from being dismissed as underpowered?

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #7

Well, to be fair, the good old American V8’s of the day sucked. This was the era when a Corvette had 135 hp or something like that. There are aftermarket products to greatly improve those old cast iron lumps, most notably heads with serious flow potential, but the stock Ford or Chevy products left much to be desired.

Since the introduction of the LS and the Modular engines, things have gotten much better, and Ford and Chevy seem to be continually pushing each other to make them better and better. Still, a Jaguar is supposed to be about grace, and there’s nothing graceful about an American V8; it’s all ground-pounding thunder.

I dunno how many of you watch Engine Power, but watching those guys dyno engines is fun! They’ll often pull some dead-stock V8 out of an American car and put it on the dyno as-is while taking bets on how much power it generates – and their bets are often in the 140 hp range. And you can tell by the sound that the engine is weak. Then they yank the heads, install some aftermarket aluminum heads with roller cam followers and rockers, then put the engine back on the dyno and get 350+ hp out of it. The difference in sound is remarkable; you can tell by the sound that the engine is now workin’ hard.

And, oddly enough, they don’t seem to care whether it’s EFI or carb. They’ll get big power numbers either way.

(ronbros) #8

well 1957, bought new a Corvette, 283 cu.in. Fuel Injection, it was optmisticly rated 283HP.

and i street raced anything with wheels, and NEVER got beat by anything from GB/UK or Europe, Jag 120/140 were a joke on acceleration and top speed, one day word was around some rich guy student from MIT university
shows up at local burger shop parking lot with a 1955 Mercedes coupe, we all went out to the 3mile divided hiway called Highland ave!

i was worried because all the reading magazines were saying unbeatable.

standing start till we run outta road,3miles, that car never had a chance , on acceleration i was gone, shiftin FULL throttle,4 speed , at over 7000revs, past torque peak was easy shiftin!

some say he was closing toward the end, my speedo read 145(optimistic), but he never got close!
so much for foreign iron, in the 1950/1960s.

and that clank box trans. he had took 1/2 hour to shift (it seemed to me).


(ronbros) #9

Kirby ,you must mean the SMOG ERA engines 135hp corvettes? dont we just love EPA, and CARB is the worst thing EVER!

these LS engines are incredable , on the utube, some have bought junkyard pickup truck LS with over 200K mies on them, put a set of turbos on them, and made out over 700HP, with out any problems!!

stock junkyard engines.

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #10

It gets better, though. Both the Chevy LS and the Ford Coyote are available as crate engines from the factory intended for supercharging or turbocharging! Lower compression ratio (around 9.5:1, I think), heavy-duty everything in the bottom end. There’s a fairly standard scheme for taking the LS and bolting on a pair of turbochargers and developing a reliable 1300 hp! That’s some serious go-fast for rational quantities of cash.

Unless you have good will power, do NOT click on the following link:


Basically, with perhaps $60K and 300 hours work, you can put a serious hurt on your neighborhood Ferrari owner.

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #11

Here’s another link:



While the initial Jaguar V12 in the XJ13 prototype displaced around 5-litres, is it known how much further the displacement was capable of being reduced to at least as far as potential V12-based variants such as the 2.5-2.65-litre V6 / Slant-6 and the 3.3-3.56-litre V8 are concerned?

(ronbros) #13

Jag had way back ,already produced a twin cam V12 4.9L, made 500HP at only 8000rpm !

torque less below 5000, ques. who drives around at 5000 & up rpm??DSCN8847

(ronbros) #14

this is my LS2 in a Buick GN, 6.0L alumninum heads stock #317. 4L80E trans, 3.73 gears !buick%20%26cute%20dogs%20017buick%20%26cute%20dogs%20012buick%20%26cute%20dogs%20003

(ronbros) #15

speaking about small V12s ,Honda produced some V12s, with the massive 1.5L for F1 GP racing.

made an unusual sound , like a whistle, scream!

i all about torque and street driving , and these DARN electric cars are breaking records any where they run!

i had a ride in an all electric Ford Mustang, 0-60 recorded 1.9 seconds, WHEW>.electric%20mustang%20001electric%20mustang%20007electric%20mustang%20005

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #16

I take it they put motors in all four wheels? Because you can’t get to 1.9 seconds driving the rear wheels only – unless we’re talking a rail in which 100% of the weight shifts to the rear under acceleration.

(ronbros) #17

NOPE , the battery packs are in the trunk behind the wheels, they weigh 300lbs alone!!

gotcha , slicks of course!


(David Jauch) #18

If I see it correctly the motor is where the engine used to be and theoretically they could even use the stock drivetrain. Transmission or not (there are two speed electrics that I know) and a very short rear end, why not, this must be very quick!
Huge tires. Weren’t the guys on Jay Leno or something? I remember the o shit lever.
Electrics somehow negate the luxury aspect of V12s.
The cooler looks too small. Where do they get their cooling? None, or air through the batteries?
Racing success or not, I think IC is more romantic, and way cooler still.

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #19

A friend of mine is on his second Tesla. The car is screaming fast but seriously heavy. As a result, it’s really hard on tires. With all that weight, it’s probably not a lot of fun to drive around a corner.

(David Jauch) #20

Not having driven one so far, centre of gravity is very low because the battery pack is below the floor. They say it handles great. But sure is hard on tires, I can imagine that… but at least in Europe you save enough gas money to afford more rubber. Definitely.
Besides, the XJ is quite heavy and has slimmer tires, so shouldn’t they be about equal? I don’t know the exact physics involved, but…