Austin-Healey 100 Six

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Austin Healey 100 Six

Austin Healey

Austin-Healey 100 Six BN4

1956 - 1959
United Kingdom
6 cylinder
102 / 117 bhp
3/4 spd. man (overdrive)
Top Speed:
100+ mph
Number Built:
10268 / 4150
5 star
Austin Healey 100 Six
Reviewed by Unique Cars and Parts
Our Rating: 5

The Big Healey

In October 1956 after great success with the 100/4, Austin-Healey announced the arrival of the new 100/6.  This car was very similar in appearance to the 100/4, but this time the car was fitted with a tuned version of the six cylinder BMC C series engine fitted to the Austin Westminster.

This "tuned" engine at first produced 102 bhp, this increasing to 117 bhp in 1957, and later that year production was transferred from Longbridge to the MG plant at Abingdon. The overdrive unit that was standard on the 100 became an option. The designers also decided to equip the new model with occasional rear seats. The wheelbase of the new car had been lengthened by 2 in (50.8 mm) to achieve this. As with other "Big Healeys" the cars are sometimes referred to by their factory designation which for this model was BN4.

A Substantial Sports Car

The Austin Healey 100 Six was a very different car from its predecessor. The standard kit included overdrive, knock-on wire wheels, Dunlop Road Speed tyres, and screen-washers. The aforementioned BMC six-cylinder engine came in its most potent form. All of this power was needed, as the Healey weighed 22cwt at the kerb which was, of course, a very substantial weight for a sports car. In fact, the word "substantial" really summed up the car. It was substantial in construction, substantial in its comfort and its road performance merited the same description.

The Austin Company succeeded admirably in providing a sports car which was also a delight to drive on tour. The Healey showed, once again, that it was not necessary to be uncomfortable when travelling really fast. The then new power plant was smooth and willing, but above all it was superbly flexible. If you were so inclined, the car could be ambled along in top gear at 25-30 mph, from which speed full throttle gave smooth and effortless acceleration.

The engine operated on a compression of 8.25 to 1, and was fitted with two S.U. carburettors. The Laycock overdrive operated on both top and third gears. On top, it gave a very high touring gear which the Healey could readily pull. On third gear, however, the overdrive ratio of 4.25 was not very different from the ratio in normal top, which was 4.1 to 1. And all this performance did not come at a big cost to the hip pocket, averaging 27 miles per gallon, or the equivalent of 33.6 ton-miles per gallon in the loaded condition, and it gives a fuel-speed factor (ton-m.p.g. x average speed) of 1,560. Both of these figures were very good. The fuel tank had a fast cruising range of approximately 325 miles.

BN4 Chassis Improvements

The increase of two inches in wheelbase and the redistribution of weight improved the road adhesion of the Healey on fast bends and corners. It was a delight to drive on winding mountain roads. Of course, this good handling flowed also from several other factors. Steering was exceptionally good, the brakes were excellent, and it maintained composure over rough roads or broken verges such that your confidence would grow the more time you spent behind the wheel.

But there were two points on which the Healey fell short of its general high standard. Although the steering column was telescopic, shorter drivers reported finding it difficult to find a gooe seating position, inevitably ending up too close to the wheel after getting their feet to comfortably reach the toe-board. The clutch and brake pedals are, to our mind, a little too close together, but we are assured that the more time spent behind the wheel, the less of an issue this would become, as you became familiar with the car. Still, foot-room remained a little confined for the driver – but perhaps that was what you would have expected from a thoroughbred sports car of the ‘50s.

On the Road

As previously mentioned, the Healey was excellent on the twisty mountain roads. The five driving ratios ensured that there was always a gear ideally suited to the hill being climbed. Good road adhesion allowed the full available power to be used for competition and offset the weight of the car to a large extent. The road speeds in the various gears, at 1000 engine rpm, were: overdrive top, 23.1 mph; top gear, 18 mph; overdrive third, 17.4 mph: third gear, 13.5 mph; second gear, 9.4 mph. The power-weight ratio with a load of 3cwt was 81.6 bhp per laden ton.

And while the Healey was fantastic in the hills, it also remained an excellent touring car. It provided both comfort and pleasant handling, combined with a very high road performance if desired. Cruising speeds were very much what the driver cared to make them. On average safe country highways the car would love to settle down to 75-80 mph, at which speed the engine was turning over quietly and effortlessly at around 3,000 rpm, with plenty in reserve. At that speed the Healey would also feel very much glued to the road. The remarkable flexibility of its engine allowed the Healey to be ambled through the towns in top gear, which felt like third in most touring cars from the time.

BMC Six Cylinder Engine
The tuned BMC Six developed an initial 102 bhp, which increased to 117 in 1957.

The Power AND The Glory

The maximum torque of 142 lb. ft. was high, and was developed at 2400 rpm which corresponded to a road speed of 55 mph in overdrive top, 43 mph in top gear, 42 mph in overdrive third, 32 mph in third gear, and 23 mph in second gear. In third gear, time for acceleration from 20 to 40 mph was 4.8 seconds, and from 30 to 50 mph was 5.1 seconds. In top gear acceleration times were: from 20-40 mph 6.3 seconds: 30-50 mph and 40-60 mph, 7.3 seconds. Acceleration in overdrive top was understandably less energetic, and from 40-60 mph would take 10.2 seconds. As we have mentioned, the 100 Six was exceptionally well balanced, with a front-rear weight distribution of 49:51, in favour of the rear wheels. That explains why the car performed so well in the hills.

But good road holding requires more than a well balanced chassis. And to that end, the Healey engineers did a superb job of sorting the suspension, such that roll was VERY moderate, and the speed tyres allowed you to enter and exit bends with plenty of speed. Somehow the Brits seemed to have found a good balance, as unlike other sports cars that ended up on Australian roads, the 100 Six remained comfortable even though it was admittedly firm, and unlike most cars that would show a Jekyll and Hyde personality when they were on rough surfaces, on the Healey the performance remained impressive – few road testers of the time needing to slow down much as the suspension would soak up poor road surfaces without allowing the car to lose adhesion. We have read many road tests, and no journalist from the time could make the suspension bottom on normal potholes, and the directional stability on loose dirt roads was described by most as outstanding.

Brilliant Steering

The cam-and-peg steering mechanism had a ratio of 14:1 and required only 23 turns from lock to lock. It was light and pleasant to use, and had that feeling of preciseness which was necessary in a fast sports car. The mechanism did not result in any pronounced over or under steer, and this neutral characteristic lent itself to adroit use of the throttle to facilitate fast cornering. There was really nothing in the way of reaction felt in the hands over bad roads, and the mechanism was free from lost motion – something usually only found on rack-and-pinion set-ups. The turning circle of 35ft was rather large for the car's wheelbase, but you could never accuse the Healey of being difficult to manoeuvre. The Girling hydraulic brakes, of course, had two leading shoes in the front drums, and the brake-lining area was 188 sq. ins.

The performance of the brakes was good, though pedal travel could be a little long. Again – maybe this was something that you would become accustomed to over time. But, what was more important was their ability to resist fade and dissipate heat. On the first point they proved exceptional, and on the second, even though they could become very hot under enduring punishment, they would always pull the car up evenly and with very little lost in overall braking performance. When you were behind the wheel, you would be able to quickly find a comfortable seating position, shorter drivers aside (as mentioned above). The sides of the car were high, and the seat was positioned low, and as a consequence protection from the wind and weather was exceptional. Not that you would be devoid of the “wind in your hair” feeling. But enough to ensure you would enjoy long stints behind the wheel with the roof retracted.

The steering column is adjustable for length and the three-spoke wheel extended from the dash almost vertically. The instruments were well laid out in front of the driver, and consisted of a tachometer and speedometer, then oil pressure, fuel and temperature gauges. Warning lights were provided for generator and the turn indicators. The minor controls were well placed along the fascia and were easy to reach and nice by touch. The self-parking wipe was accompanied by screen washers. The pedals were of the pendant style and, although as we have mentioned they were a little crowded, they did work well enough.

Behind the Wheel

The gearshift was by a short central lever with precise movement and limited travel – and the gearbox itself was a delight. Overall gear ratios were: Overdrive; 3.2; top, 4.1; overdrive third, third gear, 5.5; second gear, 7.5. Things were arranged in a particular order in the engine compartment – the engineers achieving almost perfect balance. The engine was entirely rearward of the line, and whilst the engine compartment was pretty much filled by the BMC Six, there was still enough room to make normal servicing a breeze. Bore and stroke were 79.4 by 89 mm, the induction manifold was water-jacketed and air to the twin S.U. carburettors (H4) was filtered through pancake cleaners.

The very strong chassis was supported at the front end by wishbones and coil springs under the control of piston shock absorbers and a stabiliser bar. Rear suspension was by leaf springs and similar shock absorbers located by a Panhard rod. Engine oil capacity was considerable 3 pints, no doubt the engineers deeming the volume as an aid to keeping the oil temperature down. The external body lines were particularly graceful, and as a design there are few that have ever aged as well as the Austin Healey 100 Six. Like a Penfolds Grange (or Hill of Grace for those that think the former overrated) it seems the big Healeys only ever get better with age. Internal changes included the addition of two seats for children behind the front seats, and as a consequence of the increase in wheelbase the door openings were wider and the windscreen was made a fixture.

The internal dimensions, given this was of course a high performance sports car, remained quite spacious and comfortable, offering good leg room, and an inch to spare above the head of a six-footer when the hood was erected. The hood itself consisted of a folding frame pirate canopy, and was a sonie-aSorate affair which took about five minutes to erect. It was, however, both water proof and wind proof, and sliding windows were provided in the side curtains.

When the children's seats were not in use there was a tonneau cover and supporting frame which enclosed the rear seats, and this could also be used as an extra storage compartment. And that was probably a good thing, given the boot was quite small. The fact that the small boot also carried the spare wheel, battery and side curtains meant there was only room for two mid-sized suit cases. Ventilation for both persons was provided to the front floor. There was a small shelf in front of the passenger and a pocket in the depth of each door.

A Very Collectable Classic

The Austin Healey 100 Six remains to this day a brilliant car - and one highly sought by collectors and enthusiast drivers alike. It was a rare beast that supplied ample power, great ergonomics (provided you were not too small) and ample headroom for taller drivers. The prime characteristic of the Healey was the pleasure which you derived from driving it. Its roadholding and handling qualities were very good indeed, and the car made a superb fast tourer. The BN4 was endowed with better rear-wheel adhesion than its predecessor, and the six-cylinder engine proved an exceptionally strong and flexible unit.

But, for reasons unknown to us, sales struggled from launch. Many felt the big Healey did not offer any gain in performance over the 4 cylinder model - and the occasional seating was not enough to sway the buying public. We think buyers simply couldn't justify the added cost - particularly given the smaller engined car looked pretty much the same. In 1957 the engine power was upped by the addition of a six port cylinder head providing much improved performance. In April 1958 the BN6 version of the car was introduced, this time featuring 2-seater bodywork although it still retained the longer wheelbase. Production figures were 10268 for the 2+2 100/6 (BN4) and 4150 for the 2-seater 100/6 (BN6). Production ended with the introduction of the Austin-Healey 3000 in June 1959.

These days, of course, the 100 Six is a very collectable car. Spend a few minutes behind the wheel and you will understand why.

Austin-Healey 100 Six Specifications




Years Produced

1956 - 1959

1958 - 1959

Body Type

Steel body, steel chassis


13ft 1.5 in

13ft 1.5 in


5ft 0.5in

5ft 0.5in





6 cylinder inline 2639cc

6 cylinder inline 2639cc


102 bhp @ 4600 rpm

117 bhp @ 4600 rpm


142lb ft @ 2400 rpm

149 lbft @ 3000 rpm


4 speed manual with overdrive

4 speed manual with overdrive

Driven Wheels




Drum brakes front & rear

Drum brakes front & rear

Front Suspension

Coil & wishbone

Coil & wishbone

Rear Suspension

Leaf springs, live axle

Leaf springs, live axle

Austin-Healey 100 Six Performance




Top Speed

102 mph

111 mph

0-60 mph

12 seconds

11 seconds

Fuel Consumption

22 mpg

21 mpg

Austin Healey 100 Six
Austin Healey 100 Six

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Also see:

Austin Healey 100 Six Brochure
Austin Healey 100
Austin Healey 3000
Austin Healey Heritage
Austin Healey Brochures
Donald Healey and the History of the Big Healeys
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Owned a 2nd-hand BN4 1963-66, 28000 miles on purchase. It was an oddie in that it had no o'drive and standard A105 wheels. Pulled like a train to moderate speeds but was over geared - redline top was 91mph and in 3rd the theoretical max was 70 mph. I think the gear train was bog-standard A105. Paid 975 pounds NZ for it & sold it 2.5 years later for 950. A great car but performance-wise, became seriously challenged by the new Mk3 Zephyrs, PB Veloxes et al, now that they had 4-speed 'boxes. Getting a bit embarrassing when some wide boys were driving Dad's car & wanted a race.
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