Original XJ13 - Would it have been competitive?

[XJ13]

Would Jaguar's XJ13 have seen off the Mk IV GT40 at Le Mans in 1967 if the commitment had been there from Jaguar?

In my opinion?

Yes.

Let me explain ...

Original XJ13 - Would it have been competitive?

What do you reckon?

[John Turner]

This is a question debated ever since the project was shelved, so a 40+ year discussion! The car is indeed beautiful but would almost certainly have lost some of this purity of line once contemporary aero/downforce 'enhancements' had been applied. Too heavy and probably underpowered had it been taken to the tracks without substantial development, it is unlikely to have been competitive in this form, which is stating the obvious I guess because cars were rarely competitive out of the box. So at best it has to be 'maybe'. It's another what might have been.

There are a number of replicas around and being built.

[D-Type]

I think it would have been on a par with the Ferrari and the GT40 Mk 1 (4.7) but would have been eclipsed by the 7-litre Mk 4.
Now, had it been produced in 1963 and had the benefit of 4 years' development ...

[FastDB2s]

Possibly it may have seen off the GT40 with its original 4 cam engine in 1967, definitely in 1965 but in the end the 2 valve engine gave much more power albeit 17 / 20 years later, the 4 cam engine suffering from chronic mixture burn speed problems requiring large amounts of advance.
But things were on the move so fast in that period that just 1 year or so later in 1968 a stunned world was introduced to the Porsche 917, all lined up in 2 rows, with white bodies, when they raced in 1969 every other car was obsolete, just relying on titbits when the 917s failed.

[XJ13]

Originally Posted by FastDB2s

Possibly it may have seen off the GT40 with its original 4 cam engine in 1967, definitely in 1965 but in the end the 2 valve engine gave much more power albeit 17 / 20 years later, the 4 cam engine suffering from chronic mixture burn speed problems requiring large amounts of advance.

Hi - may I ask for your source for the above claim about mixture burn? I am in possession of not only the build logs for these quad-cam prototype engines but also the results of every test conducted on the test-bed and in the three cars they were installed in (XJ13 and two MK10s). There is absolutely no evidence to suggest they suffered as you suggest.

Incidentally, Jim Eastick (who has long since retired) ran the XJ13 engine on the test-bed in 1965/66/67. He tells me they experienced no such problems.

Claude Baily himself (the engine's designer) is on record as having said as much as 800 bhp could be squeezed out of the quad-cam with further development. I can't locate his statement for now in the documents I have but there are references in Peter Wilson's definitive "XJ13" book to the engine's power potential. Pretty much on a par with the later SOHC (an entirely different engine designed primarily by Walter Hassan wheras the DOHC was mostly designed by Claude Baily).

Originally Posted by FastDB2s

But things were on the move so fast in that period

Definitely! The days of privateers and a more relaxed approach to racing at the time of Jaguar's 1950s Le Mans successes had certainly gone. It is fascinating (welll - I find it fascinating but I am sad like that) to read about the almost daily developments going on in tyre technology by the mid 1960s for example. Not just tyre widths but compounds and build as well. No doubt, these rapid changes gave chassis/suspension designers such as Derrick White of Jaguar enormous headaches as their designs needed to quickly evolve to accommodate the changes. If you look at pictures of the XJ13 in late 1967 you will see dimples/buckes in the front and rear wheelarches where they had to take a hammer to the body to accommodate the increasing tyre widths they were then fitting.

One thing that might have moved things on even faster at Le Mans may have been when the competition saw Jaguars use of the engine as a fully-stressed member (which would have beaten Colin Chapman by a few years).

[FastDB2s]

Without rereading every single book on engine development that I have - would take a couple of years or more - I cant remember, but I have read it.
Without going into chapter & verse here are some basics.
What was the max advance, if its over 27° or 28° or at worse 30° max advance at about 4000 or 5000 it has mixture burn problems, most 2 valve Hemi heads do, the problem is that its difficult to get the chamber fairly small whilst using a fairly flat top piston, one answer is to get squish to speed up the burn speed, limited in a 2 valve hemi.
Lotus twin cams run almost flat top pistons, some squish & don't have lots of advance, at least in racing form.
This is one reason why 4 valve per cylinder is so popular on road cars, shallow chambers, lots of squish, high compression, central plug & flat top pistons - all designed to reduce emissions by reducing amount of un-burnt fuel coming out of the exhaust & increasing specific power output per gram of fuel used.

Most if not all Jag sixes have burn speed problems as do Astons.
Rule is - The bigger the chamber the bigger the dome on the piston to fill it, leads to more surface area over the piston, piston shapes & angles make it worse.
Obviously there is more to it than that but that's the basic bits.

Nice looking website, nice looking book, I cant wait to read it.

[FastDB2s]

Originally Posted by XJ13

One thing that might have moved things on even faster at Le Mans may have been when the competition saw Jaguars use of the engine as a fully-stressed member (which would have beaten Colin Chapman by a few years).

I need to look at the books on the Cosworth DFV as fitted to the Lotus 49 but it was always designed as a fully stressed member that bolted to the tub & , as installed in the Lotus 49, had its (at least some) suspension mounted on the gearbox, this was designed at a similar time, 1966.
The DFV made other engines obsolete at the drop of a hat.
Heaven forbid, Jaguar may have had to consult Duckworth & Chapman to get the car to beat the Ford's with their unrivalled knowledge of engines & suspension systems respectively.

[FastDB2s]

BTW Astons had 4 valve per cylinder heads for the V8 designed fairly early on in its life albeit unofficially, long before Calloway designed their 4 valve heads in the mid eighties that AML adopted.

[XJ13]

Originally Posted by FastDB2s

the problem is that its difficult to get the chamber fairly small whilst using a fairly flat top piston

It is of course true that later improvements in engine design came with a greater understanding of combustion processes! This continues into the 21st Century.

Jaguar's engines may have had their roots in late 1940's design but still produced some very long-lived, durable and successful engines for the time. Certainly up to the rigours of endurance racing. Harry Mundy, designer of Chapman's twin-cam, worked very closely with Heynes, Hassan and Baily in the design of Jaguar's twin-cams from the outset and, for their period, were bordering on "cutting-edge". Don't forget that Hassan (ex Coventry Climax and a man who knew a thing or two about engines) joined Jaguar in 1965.

Originally Posted by FastDB2s

I need to look at the books on the Cosworth DFV as fitted to the Lotus 49 but it was always designed as a fully stressed member that bolted to the tub & , as installed in the Lotus 49, had its (at least some) suspension mounted on the gearbox, this was designed at a similar time, 1966.

Derrick White (ex Connaught F1) had designed the XJ13's rear suspension layout back in (at least) 1965. The entire rear suspension hangs off the transaxle (albeit with a pair of trailing arms each side attached to the engine/chassis mount). The ZF output shafts formed upper links. The engine was solidly bolted directly to the monocoque close to the front of the engine. The rear was supported by the bellhousing/transaxle which, in turn, were attached to the rear of the monocoque. The car was completed in 1966.

Originally Posted by FastDB2s

Heaven forbid, Jaguar may have had to consult Duckworth & Chapman to get the car to beat the Ford's

As you will know, William Lyons was talking to Colin Chapman about Jaguar acquiring Lotus in 1963 . It was the prospect of being able to run at Indianapolis in 1965 with the (still on the drawing-board) Jaguar quad-cam V12 that finally hooked Chapman. Little did he know that the engine would probably have dwarfed his car! The deal wasn't finally consummated because Lyons eventually became tired of Chapman's manoeuvrings and false claims of Lotus' level of profitability. After this experience, I doubt Lyons would have been inclined to talk again with Chapman!

[XJ13]

Originally Posted by XJ13

Derrick White (ex Connaught F1) had designed the XJ13's rear suspension layout back in (at least) 1965. The entire rear suspension hangs off the transaxle (albeit with a pair of trailing arms each side attached to the engine/chassis mount). The ZF output shafts formed upper links. The engine was solidly bolted directly to the monocoque close to the front of the engine. The rear was supported by the bellhousing/transaxle which, in turn, were attached to the rear of the monocoque. The car was completed in 1966.

A picture is probably best:

The original in 1967:


My engine at present:

[FastDB2s]

It would have needed Chapman's help with that disastrous upper link / driveshaft idea. Wonderfully cheap way of doing things.

[XJ13]

Originally Posted by FastDB2s

It would have needed Chapman's help with that disastrous upper link / driveshaft idea. Wonderfully cheap way of doing things.

Disastrous? Or elegant?

I imagine it would have had Chapman's approval because it not only did the job (and continued to do so in E-Types and various saloons) but was also lighter than the equivalents by the likes of Ford (GT40) which had an upper link as well as a driveshaft.

In fact, Chapman seems to have been pretty impressed by what Jaguar had achieved with the XJ13 as he employed the XJ13 Project Manager at the end of the project (who later became Lotus' CEO).

[FastDB2s]

By 1966 Chapman had realized the proper way to make a rear suspension geometry work & be reliable was to have an upper & lower link, plunging driveshafts which only accepted accelerating & decelerating loads not loads from the suspension being fed into the gearbox output / diff support bearings.
Although he didn't get the front suspension / brakes right until after the 72 which had inboard front brakes & a driveshaft.
Mike Kimberley is the man you are talking about, who became Lotus CEO in 2006, stepped down in 2009 because of heath issues.

[PeterMorley]

Originally Posted by XJ13

Disastrous? Or elegant?

I imagine it would have had Chapman's approval because it not only did the job (and continued to do so in E-Types and various saloons) but was also lighter than the equivalents by the likes of Ford (GT40) which had an upper link as well as a driveshaft.

In fact, Chapman seems to have been pretty impressed by what Jaguar had achieved with the XJ13 as he employed the XJ13 Project Manager at the end of the project (who later became Lotus' CEO).

Chapman used the same system in the first rear engined Lotuses e.g. 18, 19 & 20.
But they were rather lighter and less powerful cars and the next generation featured a top link some 5 years before the XJ13.

Some later Lotuses with ZF gearboxes had fixed length driveshafts but the gearbox outputs slid to accommodate driveshaft plunge.

[FastDB2s]

Chapman did use the driveshaft as the upper link on his road cars, the Europa has it, it took me forever to get it to work well enough when I turned my Europa into a hillclimb & sprint car, I constantly had to monitor the diff bearing movement / wear, the rubber bushes at the front got slung & fitted with spherical bearings & the lower arm made adjustable with rod ends to get the geometry right, should I phrase that 'as best as possible'