I have recently read a book i received for a birthday present: TWR and Jaguar's V12 prototype Sports Cars, written by Allan Scott, a New Zealander who was responsible for all engine design, development and production for the entire TWR racing effort from about 1980 to 1993. This included the XJS ETCC championship winning cars and the V12 Le Mans and Daytona winning Sports Prototype cars.
Right at the end of this period, Allan Scott designed, drew up and had manufactured a four valve per cylinder prototype V12 engine, a road -going tuned version of which was tested in a road going XJR-S. This car used a standard V12 block.
While the racing tuned version made over 590 BHP, the road tuned version made 490 BHP and loads of torque, as set out, with a photo of the engine, in the attached pdf from a page in the book. This engine was able to fit in the XJS with no modifications to the car's bonnet. Somewhere it must exist, and when Grant and I win the lottery, we will contract Allan to make us each one!
Now the interesting facts about this engine are that the four valves per cylinder layout was required for racing (had TWR continued with Jaguar Le Mans sports prototype cars - Ford by this time owned Jaguar and were not interested in pursuing that path) NOT because the 2 valve flat head was unable to produce the power. Rather, it was that for racing purposes, valve springs could not be made sufficiently robust to handle the reciprocating mass of the very large two valves over a 24 hour race. So it was valve spring breakages, rather than combustion efficiency, that required a 4 valve approach.
In fact, as Allan Scott demonstrates in this book, the V12 engined Le Mans cars were the most fuel/kilometer/average racing speed-efficient engines in any Sports Prototype racing car of the period. Le Mans and Daytona and the series they were part of were and are a fuel-limited formula for these prototype cars, and astonishingly, Allan Scott made the 2 valve V12 engine the most efficient of the lot, including their Porsche and Mercedes competitors.
Perhaps somewhat perversely, Ford, having bought Jaguar, had no interest in marketing V12 engined Jaguars as the marque's "point of difference" (i.e. its USP), and insisted upon V8 engined cars; despite having a superb TWR-Allan Scott developed 4 valve V12 engine ready to be manufactured. The photo of the engine, the eagle-eyed will notice, shows that it has the standard full flow oil cooling pipes fitted. It is also astonishingly compact. I think it was a mistake not to use it; though as much as anything, the large volume of coolant in the V12, implying long warm-up times and thus poor cold-start emissions, was the engine's real killer. But what might have been!
Incidentally, the engine in the background of the photo is a Cosworth HB Formula 1 engine, badged as a Jaguar.

 

Is there any mention of the cams? Is it still SOHC just with four valves or did they add in two more cams?

 

Tks Greg!

And it nearly made its way into a production car, namely the XJ200! In fact one XJ220 - Nigel Webb's - has had an extensive conversion by Don Law to have one of these 4-valve V12s fitted.

Paul

 

Interesting information! I love the TWR XJS's, I come back to the video of Tom Walkinshaw's Bathurst qualifying lap from '85 at least once a week. Just a few days ago I was watching it again and I was wondering what kind of heads the racing V12s used. I assume they probably weren't utilizing the 'fireball' combustion chamber of the HE's right? Interesting to hear about the efficiency of the 2-valve design despite using the flat head, then again the high efficiency was probably achieved mostly in the higher rev ranges and not so much in regular cruising speeds. Either way it's a shame the 4-valve V12 never found its way into a production car, to think what could've been..

 

The ETCC XJSs had flat heads, even though they carried the HE emblem on the boot! The two valve heads (in racing terms) had very flat torque curves and this helped fuel efficiency as well as lap times by reducing the need for gear changes. The racing rev ranges were 6,200 to 7,300 rpm or thereabouts. In the road car engines, Walter Hassan's team (developing the engine in the 1960s) found no advantage to the four cam engine compared with the two valve under 5,000 rpm.

 

It think that must have been twin cam per bank, as it was developed with Le Mans in mind, and I cannot see how a 4 valve pent-roofed combustion chamber could be driven from a single cam without so many linkages it would never stand up to the revs. I'll try to find a definite reference though.
Interestingly, it was Allan Scott's foresight that enabled the Le Mans cars to compete. As early as the ETCC XJSs, he realised that digital control of injection and timing was crucial for efficient combustion and controlling fuel usage. He backed two break-away guys originally from Lucas, and they built the electronics for the cars, right through and including the Le Mans winning Sports Prototype cars. These two eventually became Zytec, which was the Formula 1 main supplier of this era.
Allan Scott designed driver-adjustable fuelling and timing controls, and the drivers were able to (eg) select richer mixture down the flat-out Mulsanne straight at Le Mans, while dialling it back on less demanding parts of the circuit. This, together with required fuel useage/actual fuel usage readouts meant the drivers knew exactly when they could use more power and when they had to conserve fuel, etc etc.
Extensive dyno testing found all sorts of efficiencies; for example, they found that by making certain mixture and timing adjustments a 1% reduction in BHP gave an 8% reduction in fuel consumption. This sort of fine tuning was not possible in competitors' engines as they did not have the required digital control to achieve it.
This was way ahead of Porsche and Mercedes at the time, who eventually (having got the idea from a disgruntled sacked TWR driver) caught up by about 1992/3.

 

BRILLIANT Greg.

You say "compact", and since I dont have the XJS anymore, will it fit the X Type????

JUST KIDDING, what more can I want at my age than a 2.1 V6 BIG BLOCK, HAHA, I need a drink.

 

It can be made to fit. Just how much X-Type will be left at the end of the conversion is an entirely different matter...

 

The laws of physics dictate that a 60 degree V12 with much of it weight up high and in the heads would never be successful in prototype racing as it had developed. Porsche and Ferrari with their flat V12's and Cosworth and others with their short stroke compact and small turbo and simple 90 degree V8's would always have a major advantage in physics. Horse Power, more valves and romance can never overcome physics in the long run.

 

I'm gonna need some clarity on this. It had to be something else. Ford seemed to know how to do this in the 60's... their 2 valve pushrod V8 won a 24 hours race Le Mons back then with a skilled drive names Ken Miles. There was a movie about it recently and it was not a fluke, they dominated for 4 years in a row. Cadillac was soldiering on with 2 valves as recently as 2017 and was very competitive with a 6.2L V8.

 

You have to read this in the context of the times. Between 1988 and 1993 Le Mans was a fuel quantity and fuel quality (essentially pump fuel of 98 octane RON) restricted race with minimum weight limits. Thus lap-to-fuel consumption was key to winning in the Sports prototype class. Chassis technology was changing, and the TWR cars were the first sports prototype cars to use an entirely carbon fibre chassis. The combination of all this and the other points I have already quoted from Allan Scott enabled the TWR cars to beat the hitherto dominant Porsche cars over the length of the races at Le Mans and Daytona, for example, as well as many shorter (6 hours or less) events.
The wonderful cars of the Ford GT40 1960s Le Mans era cannot be compared with the formula that the Le Mans cars had to adhere to in the late 1980s/early 1990s. The point that Allan Scott makes about the 2 valve setup was that the valve springs could not take the 24 hour punishment at the revs concerned, which is why he wanted to use a 4 valve setup. The two valve setup was fine from the power point of view. Very late in the day, it was discovered that the valve springs were also being affected by a cam harmonic which was unidentified, and had this been found earlier, the springs would probably have been able to last.
The fact remains, of course, that the mass being driven by a four valve drive train, on a per valve basis for an equivalent valve area to a two valve, is far lower and thus inherently less stressful on the valve springs. The Le Mans-winning GT40 was limited to 6,200 rpm for durability and developed about 485 BHP at 69 BH/litre, a far lessed stressed engine, which was possible because fuel usage was not limited. The Jaguar car in era Allan Scott is discussing revved routinely 1000 rpm higher and produced greater power (about 700 BHP) in a far lighter chassis, and used far less fuel to produce far faster lap times.
To be able to develop the required power at the weight limit, within the fuel volume allowed, meant that an iron pushrod V8 would not be able to last 24 hours on the fuel allowance or at the speeds required to win. The GT 40 weighed 1217 kilos, the XJR-8 le Mans car about 940.
I strongly recommend the book, it is quite fascinating, and will both impress you and address your points more fully than I can do here.

 

In fact, the Porsche cars of the era concerned (1988 to 1993, Ferrari were not competing at this level) with their smaller capacity turbo charged engines were beaten by the TWR cars in both USA and European Sports Prototype series as well as at Daytona and Le Mans 24 hour races. The TWR cars won the manufacturers' championship more than once in these years. The key was the lap-to-fuel performance of the cars, given the restricted fuel quantity permitted. Allan Scott's expertise enabled the V12 engined cars to produce superior performance, though obviously as part of a package that also included a greatly superior chassis, made of carbon fibre, compared with the aluminium tubs of the Porsche cars.
Your point about CoG is well made and interestingly as explained in the book, one of the regrets that Allan Scott mentions is the refusal of Tom Walkinshaw to finance (and it was not a huge sum either) Scott's design for a new sump incorporating the main bearing caps, which mated to a new gearbox to go with it, would have substantially reduced the CoG of the package, and made the car even more competitive than it was.
The problem that the Porsche turbo-engined cars had was that fuel consumption required to produce competitive lap times over 24 hours, or even 6 hours, was too high, and leaning off the mixture grenaded the turbo engines over the course of these long races. The requirement for the use of standard 98 RON fuel further affected their long-race reliability.
The book is a fascinating insight into the design, construction and race-preparation of cars involved in top-echelon motor sport, and your questions as well as many others are very clearly dealt with.

 

i already bought the book back around 2009/2010 signed by Allen Scott himself, one thing he mentioned was keeping oil temperatures down , in long durance races!
i think i printed this a couple yrs ago !

oil cooling for V12 Jag!
also BOB TULLIUS , in America wanted 4 valve heads, but Jaguar had shut off the money , and Tom Whalkingshaw didnt want any USA help!
excerpt, from an interview, around 2012, from TUllius!

interview Tullius in America!

 

Ron
The book I am posting about is another volume by Allan Scott dealing with the later Le Mans Sports Prototype cars. I also do have the XJS book your extract is from, and as you say, what they had to do to keep oil temps down in the XJS racers was an astonishing feat of engineering. The dedicated chassis of the Le Mans cars were able to cool the oil more effectively than could be done under the ETCC restrictions that ruled the XJSs. Both books are a really interesting read, I agree.

 

You have to be very careful when you read about things when written 35 - 40 years later. The Group 44 cars at Le Mans produced about the 600 BHP mark from their 6L engines, and then had the ignition retarded at the track because of the poor fuel, so maybe 560 BHP with poorer fuel economy because they were not running in their designed window. The 725 BHP came later when Group 44 went up from 6L to 6.5L and finally 7L. And they did have the CA (California) heads by then. I have the engine log books and it shows it. The engine failures head gasket failures were of Group 44's own making, or rather their engine departments. They opened out the bores to such an extend that the coopers rings were bared to the flame front. If the flame got into the corner and burned the ring then head gasket failure / engine failure would occur. TWR did not get this problem as they left the bore slightly smaller and with that the grove in the liner had metal on the inside to protect the sealing ring, they got to 7L by a 4mm longer stroke.
Likewise with Alan Scott's book, brilliant and enlightening as it is; many of the things in there give clues as to the real truth of the situation, but please don't assume. The twin cam heads were simply designed around the most successful engine of all time the Cosworth DFV, so the tin cam heads are a DFV and a half. Even the valve train was the same, indeed the valves were DFV valves.
I could say much much more but I think Group 44 did most of the development and achieved some good results whereas
TWR did some refining before picking up the Big rewards.

 

xjr5006 you are correct , but Jaguar took the money away ,and Tullius closed shop(cant develop with out money)!!
lets face reality here , ALL competitive racing wins with Money! F1, Nascar, Lemans,etc!
ron

 

Greg true TWR did an amazing engineering for Jaguar race engines , but it never would have happened if they didnt have the money!
and a home grown modification/would never spend what they did , it would have cost more than the whole car!
OIL cooling !
ron

 

Quite so, but when I win the lottery/Grant wins it, we are dragging Allan Scott out of the weeds and getting him to build us one each and two spares! The engine fitted into an XJS with no body mods - at least as far as I am aware - so that is the real plus for me.

And go on, Tell us much more!