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Venom and the Ace 3.6?

Ace 2.6 production had hardly got under way when discussion began for the next model. American former racing driver Caroll Shelby proposed a joint venture between himself and AC for a version of the Ace with an American V8 power-plant. This was a classic story of something special being created in a joint venture largely because the timing was just right for all parties concerned. Shelby had been forced into retirement from racing due to health issues, and this gave him the chance to try something he had long hoped to do, and produce his own sports car which could be raced. The timing was even better because this was the tail end of a period when engine designs changed to much shorter strokes. As well as more power (from higher revs) this also meant engines that were physically smaller and far lighter than before. Therefore, Shelby had a chance to create something that was superior to most other Anglo-American hybrids, since it could now be done without ruining the light-weight and the weight distribution of the original car. This latter point is overlooked by those (mostly here in the UK) who deride the concept of big engines in small sports cars. The AC was different.

The timing was right for AC since this was during their engine crisis. When the Ford V8 was agreed upon, this was also very low in cost, helped by its thin-wall cast iron block, rather than using light alloys. The timing was right for Ford who were seeking to build up a much better sporting image. As it turned out, the Ford V8 engines were very competently designed and had huge potential for extracting more power while remaining durable. Initially the Ford 221ci (3.6 litres) unit was proposed, and I believe AC may have planned to call the updated car the Ace 3.6? Anyway, a 260ci became available at this time (late 1961) and this was substituted. Shelby came up with the model name "Cobra" and had a Cobra badge designed. Obtaining the supply of Ford engines was no small feat, thanks to Shelby's salesmanship and enthusiasm for the project.

The prototype Cobra was completed by early 1962. Needless to say, much initial work by AC was needed to the chassis to cope with a large increase in torque and power. The chassis gained additional tubular cross-members, heavier gauge steel, uprated suspension components, and a Salisbury differential. Total weight of the AC went up to around 18cwt (around 915kg). The first chassis was numbered CSX2000 - as usual for ACs, an "X" denoted left-hand drive - although alternative numbers are quoted in some articles. After initial testing in England, this car plus CSX2001 were shipped to the USA for further testing and development. Shelby built up an excellent team of engineers, mechanics and drivers. Their testing showed up the cars' weaknesses on the track, and AC implemented the necessary improvements. With the backing of Ford pushing for race success, this was an intensive period of design and construction work for AC.

The initial hope for the Cobra was to compete in the USA against the might of the Corvettes, and in fact the Cobra dominated this series of races with great ease, more than achieving its design objective. So good in fact, that hopes turned towards greater things: The World GT Championship. That would mean taking on Ferrari, Jaguar, Porsche, etc. and coping with the high speed European circuits. But first of all, 100 Cobras needed to be built by a deadline in early 1963 to qualify to compete in that year. AC had to suspend production of the Greyhound, Ace, Aceca and Ace 2.6 (i.e. all other models) to cope with the demand. New Cobras were built minus engine and gearbox and were shipped to Shelby in California to be completed and sold on the American market. British AC enthusiasts were getting a bit peeved about this. Only one model of AC produced and it was not available to them, and also some concern that the Cobra was marketed as a Ford, with the AC name not always mentioned. I believe this was part of the agreement with AC. The cars did at least carry AC badges on the boot lid and the steering wheel.

The Cobra's shattering performance caused plenty of excitement within the motoring press. "Road & Track" road tested one of these early Cobra 260 cars and achieved 153mph, standing quarter mile in 13.8 seconds and 0-60mph in just 4.2 seconds!

Cobra Mk. II

After just the first 75 Cobras, a mark 2 version appeared late in '62. This had a larger 289ci engine plus detail improvements to the car resulting from customer feedback. Shortly into mark 2 production, rack-and-pinion steering was introduced. The competition career of the AC Cobras has been widely published and documented, although often glossing over the input that AC made. Since this is an article about AC, I'll concentrate mostly on the British contribution.

Le Mans 1963

It was the idea of AC Owners' Club journal editor Tony Martin, to have the Sunday Times newspaper sponsor a works entered Cobra at Le Mans in '63. In fact, Sunday Times staff helped out at the race as did ACOC members, along with people from AC. Stirling Moss was team manager. A Ford-backed Shelby entry had been hoped for, but did not happen, but there was a privately entered American Cobra. A third Cobra was used for development for the Le Mans entry. All 3 cars were prepared for the race at the AC factory, with Shelby and a Ford representative (Ray Geddes) in attendance. Two of the Cobras were right-hand drive examples: Chassis no. CS2131 (not to be confused with CSX2131 although both cars were later raced by the same Willment team, and much confusion later arose over the CS2131 chassis number) for the works entry, and the other was CS2130 which ultimately did not take part. An American private entry (Ed Hugus) was chassis CSX2142. To improve aero-dynamics a little, fastback roofs were made for these cars and the windscreens were raked back to a less steep angle. This allowed a top speed of around 160mph. Both cars were effectively run as one team by Derek Hurlock and his mechanics.

There may have been scepticism about how competitive these ACs could be, but the American entry got as high as 4th overall before its engine failed during the night. Following that, the works entry backed off a little, completed the race, coming in 7th overall, 1st in the class for larger engines, and took the trophy for the first British car. Drivers Sanderson and Bolton had coped with very difficult weather conditions and avoiding a few crashes that befell others. Out of the field of 49 cars, only 12 finished the race. Ferrari, the dominant force in those days, took the first 6 places. All 3 Cobras prepared for Le Mans transferred to the Willment team.

Cobras for Europe... at last!

Frustration in the UK for a lack of Cobra availability was finally addressed when they went on sale in Europe late in 1963. These Cobras were given a different chassis numbering series starting from COX6001 (left-hand drive), and a COB prefix for right-hand drive chassis. Cobras never sold all that well in the UK. Insurance problems, high fuel costs and the Cobra's all-weather-equipment (subtle joke :) and the British weather, conspired to cause this state of affairs. Meanwhile, in the USA, Shelby's Cobras were blowing off all-comers with great ease. In all the excitement of getting into top level international racing at Le Mans, there was some criticism voiced at the lack of aero-dynamics to give the Cobra the top speed it needed to be competitive against Ferrari. Both Shelby and AC were all too aware of this need and were about to do something about it!

Brock and Turner - the Coupés

Recent changes to regulations provided scope for designing a completely new body for the Cobra chassis, while still qualifying as a production GT car. Just as long as the required 100 production cars were sold, and that the special bodies had enough room for a suitcase in the luggage compartment! Shelby gave his talented employee Pete Brock the task of creating a new body. Sports-racing bodies of this period were implementing ideas that had been around since the 1930s. Some of the best attempts at streamlining, prewar, were highly competent, but many lesser designs that appeared gave the whole topic a bad name. The basic tear-drop shape established in fluid-dynamics for low drag, has very poor directional stability when applied to a car. So, the shape needs to be changed to concentrate the bodyside area towards the rear behind the centre of gravity - much like adding a tail fin. The tear-drop style tapered tail could be truncated without adding much to the level of air resistance. Also, ducting of engine cooling air up over the windscreen could benefit flow over the screen and roof, as well reducing lift at the front.

Brock was evidently aware of all this, and how it was being put into practice by some other designers. The resulting Cobra Coupé body was a very sound design from the outset. Unfortunately, Shelby had it analysed by someone from the aero industry who was highly critical, but then, aircraft design had limited relevance here. Thankfully, the project went ahead and the Coupé proved itself capable of over 180mph. Modifications were needed to reduce aero-dynamic lift that the shape generated, including a sharpening of the nose profile and the addition of a rear spoiler. The chassis was improved for greater stiffness too. This Cobra, chassis CSX2287, handled much better at speed according to those racing drivers who knew what they were talking about.

Back in England, AC were also working on a Coupé. Contrary to some suggestions, this was not a copy of the Shelby/Brock Coupé (is there anyone AC have not been accused of copying?!) nor were the coupés joint projects. Evidently both sides wanted to see what they could do with their own talents, and both proved to be very competent. The AC Coupé project got started in the autumn of 1963 and was designed by Alan Turner. It had the special chassis number of A-98 - the chassis itself being stiffened. This Coupé was longer and lower than the American Coupé, with a nose that was very low and sharp (a bit like Turner's Greyhound) for as much front down force as possible. Ducting cooling air upwards over the screen came as a later modification, as did a large rear spoiler. As it was to turn out, the performance of the rival Coupés was almost identical and great credits to both designers.

Brock's design got its first race outing in February 1964 at Daytona. It led the fastest Ferrari by several laps before being halted by a pit-stop fire. From then on it was known as the Daytona Coupé (or "coup"!). At Sebring, it won the GT class, and the stage was set for a real onslaught on the world GT championship.

With the joys of the British winter (!), it wasn't until April '64 that the AC Le Mans Coupé was driven in anger, at the Le Mans practise sessions and even then its build was not quite complete. This was brought to an early end by a problem leading to a damaged piston. Subsequent trials on a test track could not include high enough speeds to analyse the aero-dynamics, so a test on the M1 motorway was arranged. This was also to compare the Dunlop tyres that AC had been using, with the Goodyears that were favoured by Shelby's team. It was not uncommon for this road to be used for high speed tests, when there was no legal speed limit. In AC's case, they did this as responsibly as was possible. The tests were run at dawn, between 4am and 5am, and on a deserted stretch of the M1 and suitable exhaust systems were installed to provide silencing. Both of the drivers taking part at Le Mans for this entry were involved: Jack Sears and Peter Bolton. High speeds were not maintained. Rather, a quick acceleration and then back down again. The maximum speeds reached were around 185mph. I know that both lower and higher exact speeds are often quoted, but those directly involved (including Sears) state 185mph approximately. I doubt if there was any desire to establish exact speeds (difficult anyway if speeds weren't held), or, for that matter, calibrate the speedo! The police were, in fact, in attendance, and most interested in the AC. The ACOC editor took some photos and sent them to some newspapers and this is when the storm started!

The great British press rounded the speed up to 190mph... then 200mph. One journalist tried to estimate the stopping distance from such speeds, apparently based upon braking performance of feeble saloon car drum brakes! Various journalists and motoring organisation spokes-people expressed their horror, evidently without being aware of the trouble AC had gone to in conducting the tests. Politicians got involved (oh no!) and there was talk of speed limits. After a few years, this did happen (70mph) and some still blame AC, although the mid '60s peak in road deaths probably played a greater part in this, and many other safety laws brought in. Incidentally, there was also one other Cobra given a special chassis number by AC, and this was HEM 6, a competition roadster, often since seen in historic racing in its red/gold livery. A few later examples of the CSX2000 series cars were also built specifically for competition use, recognisable by the altered bodywork to accommodate wider tyres, and peg-drive alloy wheels fitted, roll-over hoop, etc. and known as FIA Cobras. More Cobras have since been rebuilt to resemble the FIA version.

Le Mans 1964

While all that fuss was blowing up in the British press, AC and the "M1 Cobra" were busy trying to win a race. The AC Coupé had 2 Shelby Daytonas for company and these three cars were mixing with the prototypes near the front of the field, well ahead of the GT competition. AC's Coupé had lower power and higher gearing than the Daytona's - perhaps a case of AC being conservative for such a long race. Trouble for the AC entry started when it got repeated fuel blockages. Some other adjacent teams suffered this trouble and so the supply of fuel at the pits was suspected at first. Subsequently, a large amount of paper was found to have been shoved into the fuel tank!

Then, disaster struck late in the evening when the Coupé crashed. Tony Martin of the ACOC, involved with the team again that year, went with some mechanics to find the car. Track officials explained that the AC had hit several trees and rolled over 3 times. Thankfully, Peter Bolton walked away from the crash. Martin reported that the crash was caused by a tyre bursting and not through any mechanical failure. The French authorities suspected at first that the differential was the cause of the crash and the AC's diff was taken away by them. But it seems that the rear tyres were wearing through on this and other Cobras. One of the Daytonas suffered electrical troubles, but the other Daytona (CSX2299) achieved the all-important GT class victory coming in 4th overall. For AC, it was a sad end to their own project, and killed off plans to build several more Le Mans Coupés.

Cobra Coupés versus Ferrari - 1964

That second Daytona had its bodywork constructed in Italy, and this was also the case with the remaining Daytonas built - a total production run of 6. The John Willment team, already experienced with Cobra racing, wanted their own Daytona. Shelby supplied drawings and Willment got the body built on their spare chassis which was numbered CSX2131 (confusing number since the '63 Le Mans Cobra that they owned was CS2131, while CSX2131 was right-hand drive). The Willment Coupé's chassis was somewhat modified. This new Coupé made its debut fairly late in 1964 at Snetterton, UK, and achieved a GT class win. Despite these high-profile successes, the Cobras were struggling in some of the other events. It was, however, looking as though the Cobras could still win the championship, as they were catching up with Ferrari on points, but that year's final race at Monza was cancelled, denying them that crucial chance. Worse still, it looked as though Ferrari just might get their mid-engined 250LM homologated for the 1965 GT championship, plus other marques were moving forward in design, and so Shelby and AC needed to come up with something to challenge them.

Cobra Mk III - Birth of a Legend

Shelby had run a Cobra with the big 427ci engine during 1964 and hoped to go into production with this engine. The Cobra also needed a more up to date chassis too and the design for this was worked on late in the season. Ford and AC co-operated to produce a mark III chassis in a hurry, and Ford's computers at Dearborn were utilised (I suspect a slide-rule and paper would have brought equally good results!). This design was developed by Alan Turner at the AC end plus Bob Negstadt (Shelby American) and Klaus Arning (Ford). The new chassis frame had tubes increased to 4 inches from the original 3 inches diameter, and a greater wall thickness. Not a big deal, one might say, but in theory this would have tripled the basic torsional stiffness of the tubes themselves. This gain was offset by having a wider frame, but when I did some rough calculations a few years back, I reckoned the Mk. III was probably around double the stiffness of the Mk. II, torsionally.

I know that even this later frame is derided by many, especially when comparing it to the prototype sports cars of that period. But the following points should be kept in mind: Firstly, the Cobra is not a prototype, nor a new prototype evolved into a production car. Secondly, when cars featuring space-frames or stressed panelling were produced for road use, compromises in chassis stiffness could reduce them to a similar level as the Mk. III Cobra. Thirdly, the theory of efficient design in conventional chassis (i.e. under-frames) had been established by the 1940s and implemented by commercial vehicle chassis designers. Also, those car makers, such as Rover, who were far removed from specialist sports/racing car design, put the newly established theory into practice. Closer competitors to the Cobra in road car manufacture, produced chassis designs of widely varying competence. Thus, the Mk. III Cobra still compared favourably to many road sports car chassis of the day. Fourthly, the Mk. III Cobra chassis had very rigid mountings for the suspension which is absolutely vital, but not well executed on a lot of cars of this period.

The new suspension was a much more up to date double wishbone arrangement with helical springs, and I would agree with those who said that this was an overdue improvement. The whole car was also wider, comparable to my beloved 2 Litre Saloon in width and track. Everything strengthened to withstand the monster 7 litre engine's torque, plus weight saving for the unsprung mass. Alloy wheels with light weight, very wide section tyres. It is the ratio of sprung to unsprung mass that affects road holding over bumpy surfaces, and inevitably, the sprung mass was higher - being a larger car with stronger/stiffer chassis and the big engine, etc. Even so, the huge amount of engine torque was to prove a problem for maintaining rear tyre adhesion. The Cobra was the widest AC model built up to that time, at 68 inches (173cm) overall width.

The first of these 427 Mk. III Cobras was completed in the autumn of 1964. Chassis numbering ran from CSX3001 and all these cars were built as left-hand drive (although some later converted). Ford had purchased the Cobra trademark, and these 427 Cobras were not only marketed as Fords, but carried only Cobra badges with no AC badges to show who built them. Some confusion arose among enthusiasts as to whether or not AC actually built these cars, but archive photos show left-hand drive Mk. IIIs (complete with alloy wheels and competition lifting brackets) on the AC Cars production line (although one photo was published back-to-front with a "spot the error" caption!).

1965 racing season, plus 427 production

The 427 built up a reputation that is ingrained in Cobra folklore now: Fatal crashes, stories of acceleration tests, etc., problems with drivers trying to cope with so much power in a relatively light weight car. Tyre technology had not fully caught up with the demands of a super car like this one. To qualify the 427 for the 1965 GT championship, AC and Shelby had only a few months to build 100 Mk. III 427s. AC went into "mass" production (by their standards!) but could not quite do it by the deadline. Fortunately, the mid engined Ferraris also failed to satisfy the production quota, and Ferrari pulled out their works cars from the 1965 races. That gave Shelby a (relatively) easy task to bag the world GT title, not that the competition was any kind of push-over. It was still an out-standing achievement by such a small concern (admittedly backed up by Ford), and well deserved after that near miss to the title in 1964. The achievement was greatly helped by the efforts of the Alan Mann team who ran the Cobras in the European races in 1965. The high profile race at Le Mans was not a highlight for the Cobras in 1965. No less than 5 Cobras were entered but only one (the AC Cars entry, owned by the Alan Mann team) finished, coming in 8th overall.

Any hopes for a 1966 challenge with the 427s were dashed when Ford moved their full attention to the GT40 Ford cars that Shelby is also famous for his involvement with. With Shelby's interests more in racing than production cars, this brought yet another AC model to a premature end, and all the more frustrating when one considers the cult following the 427s gained much later. Building of 427s continued up to the end of 1966, with only 300 or so built. Pete Brock's project for a 427 coupé was also halted, denying us the excitement of a 220mph Cobra at Le Mans. 427 Cobras still raced, even here in the UK, often with success. Some cars actually had the 428ci Ford Galaxy power unit installed.

As to performance, a UK registered 427 got into the Guiness Book of Records in 1969 as the fastest accelerating production car in the world. It achieved 0-60mph in 4.2 seconds. This record stood for 20 years. Top speed of 427s was limited by gear ratio and usually quoted as 165mph. 0-100mph could be achieved in under 9 seconds. The more enlightening standing quarter mile times were a little over 12 seconds, although sub 11 second times were achieved on racing tyres. Other 427s recorded 0-60mph times of 3.8 seconds! Chassis numbering ran from CSX3001 to CSX3355, but with a short series of numbers (CSX3056-3100) missed out and resuming from CSX3101. Presumably the initial series were the competition cars intended to gain homologation for the 1965 GT championship. When that failed to happen, most competition Cobras were sold as semi-competition ("S/C"). 'Ordinary' (!) 427 road cars then appeared from chassis CSX3101 onwards.

It is worth emphasising that the AC/Shelby Cobra was very much a joint effort, from the design and building work of Tojeiro and Davison (who both joined AC), to Turner's development work on both the Ace and Cobra (not forgetting that great roadster body style - if only AC had registered the design!). The craftmanship of AC's chassis and bodywork building. Then, Shelby's original inspiration and his talent to make things happen. Followed by Shelby American's intensive race development. Most importantly, this project would not have got so far without the considerable financial support of Ford, as well as the very durable V8 engines that they had developed. No doubt Ford's interest was intensified by the lack of love lost between them and Ferrari, following the aborted attempt by Ford to purchase the Italian manufacturer. A little hate can go a long way!

One last footnote (apologies for the pun!) is that the Cobras were the last ACs to feature the lovely cast aluminium pedals with the AC logo, that had been a feature of ACs from the 1930s.

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