427 AC Cobra

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AC

427 AC Cobra

 1961 - 1968
Country:
United Kingdom
Engine:
Ford V8
Capacity:
6998cc / 427 ci
Power:
425 bhp at 6000 rpm
Transmission:
4 spd. manual
Top Speed:
frightening
Number Built:
341
Collectability:
5 Star
The idea of putting American engines into European chassis was nothing new. You could go back in history and find early examples of Railtons from the 1930s and Allards of the 1940s and early 1950s to see the formula being used. In the 1960s the ultimate interpretation of this formula came in the form of the 427 AC Cobra. At the time, the Cobra was generally considered to be the fastest-accelerating road car ever built, given its maximum speed of about 162 mph with the standard 3.54 axle ratio, but in truth there were a few even faster, such as the Ferrari Daytona.

With many exotic cars, the price of ownership usually includes the proverbial financial black hole. But this was not so much of a problem with the Cobra, as the major components (such as engine and transmission) were Ford and therefore readily available at reasonable prices. Collectability was also another attraction, given that only 341 Cobra 427s were built. In fact, there probably won't be anything like them ever built again, because cars of this nature are not only illegal now but considered by many to be downright antisocial.

Carroll Shelby



Cobras were built in England by AC Cars during the mid-1960s, and it was retired race driver Carroll Shelby who got the whole thing off the ground. At the time AC was building the Bristol with a 2-liter six in a chassis that dated back to 1954. Shelby came up with the idea for using a Ford V8 in the good looking roadster and modifying its body to make it look even better. The first few cars were built using Ford's 260-cubic-incher, but the rest came with the high-performance version of the 289, a popular option in the original Mustang.

With Ford's backing Shelby started an extensive and very-successful racing program which led up to winning Le Mans. Along the way he decided that Ford's 427 engine was just the thing for winning races as well as powering road cars. We can’t think of any manufacturers, regardless of size, that would have lent an ear to someone explaining how they wanted to shoehorn a V8 into their roadster, but AC cars was a sort of cottage industry and adaptable even to crazy Texans. It was time to redesign the chassis anyway, so a new layout was conceived to Shelby's specifications. The resulting car incorporated a large-diameter, ladder-type tube frame. Suspension was independent all around, using unequal-length A-arms and coil springs front and rear. The brakes were discs, 11.63 in. in front and 10.75 in. in the rear. The wheelbase was 90 in. and the curb weight was 2530 lb.

The original tires fitted to most Cobra 427’s were 8.15 x 15 Goodyear Blue Dot, mounted on Halibrand knock-off magnesium wheels. The 7-liter engine put out 425 bhp at 6000 rpm and 480 lb-ft of torque at 3700 rpm. There was considerable confusion at the time about the various types of 427 engines, some of which were actually 428s - a very different engine. The 427 was a "side-oiler", with cross-bolted main bearings. Carburetion was through two 4-barrels, which were surprisingly economical at low speeds because the 2500-lb car would cruise on just a whiff of mixture. Of course if you opened it up, the eight barrels would turn a trickle into a torrent, with the resultant loss in fuel consumption, but then that was the whole point anyway.

Behind the Wheel



Some owners noted that the main problem with their 427 involved the starting up procedure. The carburetors were unchoked, and there was a possibility that they could catch fire if the engine stalled while still cold – so owning one in a colder climate came at a price. The driving position was comfortable, with plenty of room for tall people. The only criticism was that because of the size and location of the engine and transmission, the pedals were offset appreciably to the left and the shift lever was positioned too far back. Obviously the location of a 7-liter iron engine in a car of this size was critical, because you could easily have a nasty polar moment of inertia if it weren't positioned just where it should be. The front/rear weight distribution was 48/52% without driver – so it was near perfect.

Considering the torque of the engine, many road testers had pre-judged the 11.5-in. clutch to be a real beast, and all were pleasantly surprised to find it very light and it took up very smoothly. The transmission was also brilliant, you could find a ratio for any occasion among the four speeds. The engine idled at a steady 800 rpm when warm and the rumble would shake your tooth fillings loose – which was a good thing. A fortunate characteristic of the 427 engine was that, despite all the carburetion and the sound at idle, it was extraordinarily flexible and could probably pull a freight train at 2000 rpm. Not only did this characteristic make the car easy to drive, but it also meant that you could keep the secondary barrels - which are the noise makers - out of contention. The steering was quick, at 2.5 turns lock-to-lock, and heavy when moving slowly because of the amount of rubber on the ground.

From the styling point of view, the car was exactly in keeping with its character because it looked mean as hell, whether coming or going. None of your sleek, sexy Italian styling for Carroll Shelby and his men, but just a bundle of brute force covered in aluminum wrapping shaped to fit, flared and bulged where necessary. As far as creature comforts were concerned, they were minimal. The cockpit ventilation was inadequate, but then 400 plus horsepower represented a lot of heat to be disposed of. The noise could also become tiresome on a long trip, but there was nothing you could do about it because there was no room for adequate mufflers and the tail pipes, for the same reason, had to exhaust in front of the rear wheels. The top offered adequate protection, but assembling it was not so easy. The 427 was fitted with a heater, but we have been told that the heat from the engine was enough to keep you warm – so it was really an unnecessary addition.

Torque on Tap



Service accessibility was surprisingly good because the car was just basic machinery and therefore uncluttered by air conditioning, power steering and all the other devices that got in the way of a mechanic. However, one slight failing was that you had to remove the right cylinder head to replace the battery. Once you were away from the burbs, you were ready for the moment of truth, but it was essential to proceed with caution and respect. Unlike most other fast cars, it wasn’t the 425 bhp but the 480 lb-ft of torque at 3700 rpm that got you into trouble. It's torque that spins wheels, and on the Cobra the torque came in very early and without much warning at all. But the great thing about torque is that it doesn't really matter what speed you are going or what gear you are in—there's always a bit of urge left.

At the time the 427 Cobra was introduced it was fashionable to record times from zero to a hundred and back down to a complete stop for fast cars. The record was then held by Aston Martin at slightly under 25 seconds, but the late and much lamented Ken Miles, who was a Cobra driver and developer, went out and did the job in 13.8 seconds. Miles proved that not only did the car go, but it also stopped as well. While many thought the Cobra just had to be crude, it was far more refined than most. For example, the suspension was excellent on good road surfaces, the brakes were superb and the steering extremely accurate. On poor surfaces the car tended to leap about and scratch for traction and you could break traction very easily when accelerating hard on any surface.

There was nothing particularly treacherous about the car's basic handling qualities, because it was a neutral machine as far as oversteer and understeer were concerned. But with two 4-barrels it was all too easy to activate a few more barrels than you actually needed. The trouble with the Cobra was simply its power, which was not really the cars fault at all, but the person behind the wheel. There was always that temptation lurking under the hood, and using it could be dangerous in the wrong conditions.

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