AC Cobra

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AC Cobra

 1961 - 1968
United Kingdom
Straight 6 (AC/Bristol/Ford)
102/125/170 bhp
4 spd. (optional overdrive)
Top Speed:
187 km/h
Number Built:
5 Star
AC Cobra
Reviewed by Unique Cars and Parts
Our Rating: 5

A potent car with a chassis good enough to handle the enormous power. Fortune favours the brave - and the brave drive a Cobra.


AC Cars were approached in 1961 by Texan racer Carroll Shelby, with the idea of putting a Ford 4.2-litre V8 engine into the Ace sportscar. A few months later the first prototypes were produced with 100 being sent to America a short time later for completion. The result of this was the legendary Cobra, one of the fastest and most famous muscle cars of all. This handsome two-seater sportscar with its relative light body weight and high torque pushrod V8 engines, produced amazing performance.

Earlier versions used a 4.2-litre engine with a top-loader gearbox which Shelby later changing to a bigger 4727cc motor. This increased power from 164 to 195bhp with top speed of this model being 222 km/h and 0 - 96 km/h achieved in 5.5 seconds. This car first became available in Britain in 1964 with four-wheel discs amongst it specifications. Eventually rack and pinion steering was introduced (when the 289 engine replaced the 260). In 1965 a seven-litre cobra was produced with a 6989cc engine resulting in the fastest accelerating production car in 1967 (0 - 96 km/h in 4.2 seconds).

The Cobra 428 (this is not a typo - see below for an explanation) version resulted in a virtually all-new machine with fat arches front and rear housing huge Goodyear tyres. The doors and bonnet were the only similarities with the 289 with the chassis being re-designed and coil springs were used instead of the old leaf springs. The Cobra production ceased in 1968 during which 4.7 and 7-litre cars were running at the same time. Since 1965 the "baby" Cobra has been recognised as the AC 289 Sports which used the same flared-arch body as its seven-litre cousin. In the United States both Shelby and Ford Cobras were grouped together as Shelby American Cobras.

The Cobra 427

The idea of putting American engines into European chassis was not new, not even when the Cobra 427 ruled the roads. Early examples were the Railtons of the 1930s and the Allards of the 1940s and early 1950s, and the results could be more than satisfactory if the car was designed and engineered as a whole. And as a car designed as a whole, the Cobra certainly qualified. At the time it was considered to be the fastest-accelerating road car ever built with its maximum speed of about 162 mph – and with the standard 3.54 axle ratio it could only be bettered by a few exotics such as the Ferrari Daytona.

As we all know, 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 Cars were building the Bristol with a 2-litre six in a chassis that dated back to 1954. Shelby came up with the idea for using a Ford V8 in this handsome 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 Carroll 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. You can only imagine the look on AC boss William Hurlock's face when ol" Shelby walked in with a 427 under his arm. If it had been someplace like Porsche, he probably would have been told to kindly take his nasty hunk of iron away, but AC cars were a sort of cottage industry and adaptable even to crazy Texans.

A Chassis To Shelby Specifications

It was time to redesign the chassis anyway, so a new layout was conceived to Shelby's specifications. The basis of it was 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 inch in front and 10.75 inch in the rear. The wheelbase was 90 in. and the curb weight was 2530 lb. The original tyres were 8.15 x 15 Goodyear Blue Dot. mounted on Halibrand knock-off magnesium wheels. The 7-liter engine put out a whopping 425 bhp at 6000 rpm and 480 lb-ft of torque at 3700 rpm. There remains to this day considerable confusion about the various types of 427 engines, some of which were actually 428s - a very different engine.

The genuine 427 was a "side-oiler" with cross-bolted main bearings. Carburetion was through two 4-barrels, which were economical enough at low speeds because the 2500-lb car would cruise on just a whiff of mixture. When all eight barrels were open, however, it was like Niagara Falls in the manifold. The exhaust system was a rare beast - quiet when you needed it to be so that you could (almost) drive in a clandestine manner so as not to draw too much attention from the boys in blue - but when you needed it to, it could make lots of noise so essential for the full enjoyment of sports-car driving. Starting the Cobra 427 was not the easy turn-the-key operation you would have expected - the main problem was that the carburetors were unchoked and could catch fire if the engine stalled while still cold. In cold weather it would always stall at least once before setteling into a slightly rich running idle.

Behind The Wheel Of The Cobra 427

The driving position of the Cobra 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 and the shift lever was comparatively far back. However, these faults were easy enough to get used to and didn't greatly affect the driving experience. Obviously the location of a 7-litre iron engine in a 2500-lb car was critical, because a nasty polar moment of inertia was likely if it weren't positioned just where it should be. The front/rear weight distribution was a brilliant 48/52% without driver. Considering the torque of the engine, you might have expected the 11.5-in. clutch to road testers of the time claimed it was actually it is very light and took up very smoothly.

The transmission was one of the best then going - 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 was enough to shake your garage to its foundations - perfect for showing the lads over a cold bevvy. A fortunate characteristic of the 427 engine was that, despite all the carburetion and the thumping sound at idle, it was extraordinarily flexible and could probably pull a freight train at 2000 rpm. Not oniy 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 Cobra 427 was in keeping with its character because it looked mean as hell, whether coming or going. None of the sleek, sexy Italian styling for Carroll Shelby and his men - 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 had the potential to 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 all that easy. There was a heater, other than the engine, but it this was only really needed in the coldest of climates. Some owners fitted a radio, but quickly discovered it impossible to hear over the noise of the engine.

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 get in the way of a mechanic. However, one slight failing was that apparently you have to remove the right cylinder head to replace the battery. Once you are away from human habitation, you are ready for the moment of truth, but it was essential to proceed with caution and respect. Unlike most other fast cars, it was not the 425 bhp but the 480 lb-ft of torque at 3700 rpm that could get you into trouble. It's torque that spins wheels, and the torque came in very early and without much warning.

Cobra 427 Performance

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 Ken Miles, who was a Cobra driver and developer, went out and did the job in 13.8 seconds. Not only did the 427 go, but it also stopped as well. Owners claimed you would drive around slowly to get everything warmed up and then put your foot in it in 2nd gear. Instantly the Cobra 427 would be transformed from a lumbering, heavy monster into a ballistic missile. A cacophony of noise and tyre smoke as the tachometer hit 6000 rpm, and you could do it all again in 3rd gear - provided you didn't need to pull over and empty your pants. For the very brave, and un-soiled, you could do it again in 4th. 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.

By the standards of the day the Cobra 427 was a rather crude car - and judged by todays standards it was downright agricultural. A handful to drive because of the enormous power, it was also a car that rewarded the brave. You could push hard, the suspension being excellent on good road surfaces, the brakes were superb and the steering extremely accurate. On poor surfaces the Cobra 427 would tend to leap about and scratch for traction and you could break traction very easily when accelerating hard on any surface. That said, however, there was nothing particularly treacherous about the car's basic handling qualities, because it was strictly a neutral machine as far as oversteer and understeer were concerned. However, the whole question was somewhat academic because if you were feathering it through an high speed corner and started sticking your foot in it, physics would take over as 480 lb-ft or a multiple thereof hit the rear wheels.
AC Cobra

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Also see:

AC History
427 AC Cobra (USA Edition)
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