Morris Minor MM: how Alta added spark to the sidevalves

By Jon Pressnell

| 29 May 2024

Classic & Sports Car – Morris Minor MM: how Alta added spark to the sidevalves

Behind the excitement of the 1948 unveiling of the new small Morris designed by Alec Issigonis lay a story of disappointment.

There was a fashionably American-inspired monocoque body design, independent front suspension by torsion bars, and one of the finest rack-and-pinion steering systems yet created.

But under the bonnet lived the Morris Eight Series E’s plodding 918cc sidevalve engine, a 1930s design cribbed from the Ford Eight power unit and delivering 27.5bhp.

The supercharged 1949 Morris Minor MM (closest) makes a splash, while the standard car (middle) struggles to keep pace; the tourer is breezy and responsive

The sweetest-handling of British saloons was hobbled by an engine unworthy of its chassis.

Issigonis had intended the Morris Minor to have a flat-four, and experimental engines were built (see below).

But in 1947 management pulled the plug on the project, which also encompassed a bigger flat-four for the future Morris Oxford.

A sidevalve adaptation of the smallest of the overhead-cam units then being developed by Morris Engines Branch was briefly considered, as was an enlarged 970cc Morris Eight sidevalve.

The standard Morris Minor MM is smooth but leisurely

Another thought was to drop in the pushrod version of the Series E engine already found in the Wolseley Eight.

Developing a rather more handy 33bhp, this became the favoured option.

But existing tooling was insufficient for high-volume manufacture, and after a period of time-wasting hesitation there was a new-found sense of urgency about getting the Minor into production.

The overhead-valve Wolseley engine would have to wait.

Early Morris Minor MMs use the sidevalve engine from the Morris Eight

Driving Terry Blissett’s standard 1950 MM saloon brings the issue into focus.

Rescued from a barn in 2016 and restored to concours-winning level, it is both a delight and a challenge to drive.

The engine is pleasantly refined, and low gearing combined with an abundance of bottom-end torque makes for excellent drivability: you’re straight into second gear and then third, in which you can happily trickle along.

That long, direct-acting gearlever with its mushroom-headed knob clunks each ratio sweetly into place.

Morris Minor MM wheels featured a distinctive coachline until 1951

Only if you rush will it catch; a gentle pause as you change and you won’t beat the synchromesh.

Despite being no lighter than the Morris Eight Series E, Terry’s MM seems to manage rather better on the same modest sidevalve engine.

Perhaps superior aerodynamics have something to do with it. All the same, it is always on the margins.

It will bowl along on a flat road at a contented and refined 50mph in fourth, and with a slope just slightly in your favour you can manage on a relatively small throttle opening.

The home-market Morris Minor MM had low-set 5in headlights until January 1951

But even with foot to the floor you’re working to get the car to exceed that speed by very much.

Hit a slope that’s against you, and the power deficit really tells: unless you marshal those limited resources, momentum will fall right away, although the low-down torque means the car will lug slowly up.

“You have to anticipate, read the road and get your foot down before a hill,” says Terry.

“You never ought to go anywhere in a hurry.”

‘Recalibrate to the Morris Minor MM’s rhythm and you discover a happy-natured little car with sharp brakes and precise steering’

Recalibrate to this rhythm and you discover a happy-natured little car with an easy clutch, sufficiently sharp hydraulic brakes and deliciously precise steering allied to poised, roll-free handling.

Sitting high on that bar-stool bucket seat, guiding the slender-rimmed wheel and contemplating the aesthetically perfect Issigonis-designed dashboard, the cockpit of an early Minor isn’t a bad place to be.

All that’s missing is more power.

A ‘Silver Top’ head from famed purveyor of go-faster bits Vic Derrington was one period solution, and could be accompanied by a twin-carb conversion and a special Derrington exhaust.

Vic Derrington’s Alta-head-equipped Morris Minor MM leads a Standard Ten and a Ford Anglia 100E in the 1956 BARC Members’ Meeting at Goodwood

But from 1954 the ultimate bolt-on goody for the Minor was the Alta aluminium overhead-valve cylinder head.

Devised by manufacturer of racing engines and race-car constructor Geoffrey Taylor, after the 1956 closure of Alta it was marketed by Derrington until the mid-’60s, with HRG latterly taking over manufacture.

Derrington quoted an output of 38bhp for an Alta Minor with standard carb and exhaust – good enough, he suggested, to raise maximum speed from 62mph to 75mph and reduce the 30-50mph time in top from 31.6 secs to 17.2.

This peppy Morris Minor MM tourer has an Alta cylinder head

Priced at £43 10s in 1954, rising to £52 10s in 1961, the conversion was expensive – and that was before fitting.

You could also carry on spending: add a twin-SU carb conversion and Derrington’s ‘Deep Note Exhaust’ (this last boosting power by a claimed 15-20%), and output rose to 44bhp for an additional outlay of £31 5s.

Substitute an extractor-type racing exhaust manifold and you could hit 49bhp and an 89mph claimed maximum.

The ultimate race-tuned engine, with 9.5:1 compression, extractor-type exhaust manifold, larger inlet valves and bigger SUs, was good for ‘over 52bhp’ and 94mph ‘under favourable circumstances’.

This modified Minor MM tourer has neat details, such as guides for the plug leads

The total cost of this kit was £93 15s – excluding the full balancing of the bottom end that was desirable if the engine was to stay in one piece under its newly doubled output.

Also suggested was a higher 4.22:1 back-axle ratio, a suitable diff being available through Derrington.

Contemporary reports confirm the Alta head conversion’s effectiveness.

Particularly enthusiastic was John Bolster’s 1954 Autosport test of racing driver Alan Foster’s Alta Minor, which he dubbed ‘exhilarating’.

Up to 1950, the waist strip on Morris Minor MMs had a thick stripe

Interestingly, this was with a single-carb installation: Bolster wrote that no advantage was to be gained by fitting a twin-SU conversion – a Taylor-era opinion at odds with that of Derrington, who claimed twin carbs gave an additional 4-6bhp.

Bolster reported: ‘Providing the revs were kept up, the little vehicle was very lively in traffic, and as soon as I reached the open road I settled to a cruising speed well above the original maximum.

‘The engine is no noisier than standard, though the exhaust has a rather more powerful note during hard acceleration.’

The Alta-head Morris Minor MM tourer’s pace is up with a 948cc A-series Minor

‘The performance is improved out of all recognition, and I was at last able to make full use of that outstanding roadholding,’ he continues.

‘Travelling three-up, I was able to average close on 60mph for quite a long cross-country journey.

‘The incredulity on the faces of some of the people I passed had to be seen to be believed’.

Bolster recorded an averaged-out maximum of 76.5mph – ‘a colossal speed for a 1-litre four-seater saloon’ – and clocked 0-50mph in 13.4 secs, with 60mph coming up in 20.4 secs.

The head conversion was first conceived in 1954, then produced by Derrington and later HRG after Alta closed in 1956. The kit boosted power from 27.5bhp to 38bhp

These figures were with a corrected speedo: at a genuine flat-out 78mph, the Minor’s optimistic dial read an impress-your-neighbours 86mph.

Fuel consumption with a rich needle fitted hit a low of 24mpg with sustained high-speed cruising, but improved to around 30mpg at a 65mph cruise.

On a weaker needle, said Bolster, up to 45mpg was claimed by Alta.

Meanwhile, The Motor found that at lower speeds the Alta Minor was actually more economical than a sidevalve car, and that consumption only fell towards 30mpg in very fast driving.

The Shorrock C75 supercharger in this Morris Minor MM delivers impressive performance

That was then – and with a doubtless race-standard installation.

Ray Newell’s Alta-head ’49 MM tourer can be considered representative of what the conversion can deliver without any special fingling – and with a single SU on the standard manifold.

The transformation is frankly astounding: suddenly there is zing in every gear and the engine picks up beautifully.

It’s instantly responsive, revving crisply and delivering power with no hint of sluggishness.

This supercharged Minor MM is one of the hottest takes on the Morris sidevalve engine

You’re soon cruising at 45-50mph on a much smaller throttle opening than in a standard car, and at 55mph you’re still pulling; at that speed in a factory MM you’d likely be on full throttle and timing your acceleration with a calendar.

In more hilly terrain the Alta-powered Minor climbs comfortably, perhaps still putting on speed, when the sidevalve car is running out of puff and demanding a downchange.

On give-and-take roads the Alta Minor lets you go as quickly as you would safely in any later A-series Minor 1000, and with no loss of refinement.

The cabin of the Morris Minor MM is simply trimmed, but lifted by its US-influenced dashboard

With an alloy head and two-piece pushrods, there’s a metallic quality to the soundtrack lacking in the more plodding, all-iron sidevalve engine, but it’s never displeasing.

“The conversion completely changes the feel of the car and makes it so much more usable,” says Ray, whose Minor is one of perhaps 20 currently fitted with the Alta head.

“I had a Derrington Silver Top on a previous car, and there’s no comparison.

“Fitting an Alta head is probably the easiest way of getting 948cc performance out of the 918cc Minor – in particular the acceleration in the gears, rather than any increase in top speed. The pulling power in third gear is really impressive.”

‘Lowlight’ Morris Minors have a chrome grille

Revealing the performance that can be unlocked by the Alta head is Keith Luck’s 1949 supercharged saloon.

Lightened, balanced and with a tubular four-branch exhaust, the engine employs a Shorrock C75 supercharger fed by a 1¼in SU carburettor.

With 4psi boost, that lot amounts to just over 65bhp on a rolling road.

When we sample the Platinum Grey car it is not happy: the mixture is out of sorts, the plugs foul and there is a lot of spitting back.

This supercharged Morris Minor MM sports a boost gauge and rev counter

Despite those challenges, the extra muscle is immediately apparent, with an easy 55-60mph on the straights accompanied, as you might expect, by a more robust soundtrack.

In similar road conditions, Keith’s blown Minor MM feels good for at least an extra 10mph over and above Ray’s standard-tune Alta car.

“The supercharger transforms things,” says Keith. “You get the benefits of the Alta head – more drivability – then the blower comes in at the top end.

“The combination of Alta head and supercharger gives lots of torque through the gears, and acceleration that keeps up with modern traffic and holds speed up hills.”

‘The blown Morris Minor MM highlighted how full of zest a more modestly specified Alta-tuned Minor could be’

Notwithstanding the engine being as off-colour as the weather on the day of our photoshoot, the appeal of a blown Alta-head Minor MM not only shines through, but also highlights how competent, sweet-natured and full of zest the more modestly specified Alta-tuned Morris can be.

You can see why it was such a well-regarded conversion in its day.

But let’s square the circle.

Years ago, I was able to do a comparison road test of a Morris Eight Series E and a Wolseley Eight, two cars in effect identical but for their engines.

The Alta overhead-valve cylinder head was the ultimate add-on for the original Morris Minor MM

The overhead-valve Wolseley unit was peppily brisk, and I would say that its performance advantage and general character were very similar to what you experience with an Alta conversion.

Put another way, if it had got its act together, the team at the Nuffield Organization could have had a properly engined Morris Minor in production from the very beginning.

The Alta head conversion shows how good such a car could have been.

Images: John Bradshaw

Thanks to: Morris Minor Owners’ Club and Alta-head expert Graham Holt

Geoffrey Taylor and Alta cars

Geoffrey Taylor in his Alta at Brooklands © Getty

The Alta story starts in Kingston upon Thames, Surrey, in 1927, when Geoffrey Taylor, a young engineer working for the ABC car company, decided to build his own sports car from scratch.

By November 1928 the car was ready, right down to a homebuilt 1074cc all-aluminium twin-cam engine, all created in the stable block of the family home.

The car was named Alta, after a town in Alberta, Canada, which Taylor had come across in a novel.

Taylor subsequently set up the Alta Car and Engineering Company in January 1931, and between then and 1935 he built 12 Alta ‘1100’ sports cars.

He also devised his own Roots-type superchargers and developed an improved 1500cc version of his engine; from that came a run of six 1500cc racers and seven roadgoing sports cars.

The ultimate pre-war Altas followed: three supercharged racers with all-independent sliding-pillar suspension, the best capable of challenging the works 2-litre ERAs.

Government contract work and developing Ford’s V8 for marine use kept the Tolworth works busy, while a further earner was an Austin Seven aluminium cylinder head that showed the potential for bolt-on tuning gear for popular cars.

Approximately 2000 Morris Minor MMs were fitted with Alta cylinder heads

Post-war, Taylor built a run of 1.5-litre supercharged Grand Prix cars, and from these he developed an unsupercharged 2-litre car for Formula Two.

The unblown unit also powered the successful HWM racers and was used by Connaught, and it was this use of Alta engines that thrust the firm to prominence.

The 2.5-litre Alta unit powered the B-series Grand Prix Connaught, and this car, driven by Tony Brooks, took a historic GP win at Syracuse in 1955, marking the beginning of Britain’s establishment at the forefront of Formula One.

In 1956, after completing a last batch of 2.5-litre engines and dogged by ill-health, Taylor closed the Alta works.

By that time he had diversified into the overhead-valve Morris head, which was launched in 1954.

Few writers bother to mention this in their reviews of Alta history, despite estimated production of around 2000 heads.

Morris Minor: the flat-four engine that never was

Morris Minor packaging drawings demonstrate the space-saving advantages of the flat-four (top) compared with a conventional in-line engine; a torque-tube and split propshaft were also proposed © BMIHT

The flat-four engine envisaged for the Minor was conceived in two capacities – 800cc and 1100cc – and was a cast-iron sidevalve unit.

But why a flat-four? A horizontally opposed engine is smoother and better-balanced than an in-line unit, but a more fundamental advantage is compactness.

Because the engine is shorter, the crankshaft and crankcase are more rigid, plus the engine isn’t as tall so the centre of gravity is lower.

Every bit as valuable is that a compact engine takes up less space in the vehicle, and for Minor creator Alec Issigonis few things mattered more.

The engine was indeed small – 13in from crank pulley to flywheel – and narrow, thanks to its old-fashioned sidevalve configuration, chosen by Issigonis for precisely that reason.

By September 1945, the original ’43 prototype had been fitted with the first experimental flat-four, which, evidence suggests, was of 800cc.

Subsequently an 1100cc unit arrived and was tried in another pre-production car.

Surviving engineering drawings from 1946 depict two different versions of the 800cc engine, one called YF80M and the other ZF80M.

The ZF80M is a dry-sump design with a separate oil tank, one pump to distribute oil to the bearings and a second ‘scavenge’ pump to return it to the tank.

This expensive solution makes the engine less tall, for a still lower centre of gravity.

It appears that at least one dry-sump flat-four was tested in the ‘Mosquito’ prototype, but it’s hard to imagine the Morris accountants being enthusiastic about such elaborate engineering.

Vertical starter and downdraught SU carburettor for Morris’ YF80; the compact column-change gearbox is mated to a long tailshaft and short one-piece propshaft © BMIHT

YF80M is a more orthodox wet-sump design. As with the dry-sump engine, it had two main bearings.

With the shorter crank of a flat-four this isn’t necessarily a disadvantage if the mains are sufficiently beefy – and to add a centre bearing would increase the engine’s length.

According to Jack Daniels, right-hand man to Issigonis, the crank had generously proportioned main bearings and never gave any problems.

The engines acquitted themselves well, according to Daniels.

“We tested mainly the 1100, and that gave reasonable performance – much better than the Morris Eight engine,” he said.

“It was pretty good. You were conscious of a flat-four exhaust beat – a bit off-key and different from any other engine – but you got used to it.”

Former Morris Engines employee Fred Collis remembered his father driving a prototype with the flat-four from Coventry to Cowley.

“He said the car was marvellous and had far more speed than a Morris Eight,” he recalled. “He was very impressed by the performance.”

One-time Nuffield engineer Jim Lambert’s recollection was less rosy, but he was in his early 20s then and all he knew about the flat-four was secondhand.

“I don’t think it had a chance,” he said. “It was gutless and wasn’t any real advance on what we had. It wasn’t a big step forward.”

The experimental engines did have vibration problems, apparently caused by a poorly located flywheel.

Former Morris Engines employee John Barker recalled other failings: “Engineers in the experimental department said it died a death because of bearing trouble – the bearings were too noisy.

“I was told there was crankshaft whip, I believe because with only two main bearings there wasn’t enough support for the crank.”

Any tendency for the crankshaft to whip in extreme circumstances would have been exacerbated by vibrations from an out-of-true or loose flywheel.

Such development problems would normally be ironed out quickly, had time, resources and management goodwill allowed.

Morris’ ZF80M engine, with two oil pumps and no conventional oil pan; angled heads may not have been used; the pistons have recessed bowls © BMIHT

It wasn’t that simple, though. The flat-four was going to be expensive to produce.

In July 1947 it was calculated that the YF80M and its four-speed column-change gearbox would have cost just over £47 to manufacture; the Morris Eight engine and gearbox was costed at £38, making the boxer unit a whacking 24% costlier.

Worse, from Morris Engines’ perspective, it ‘wasn’t invented here’.

The division was struggling to put a family of in-line engines into production, including the 1000cc and 1100cc ‘fours’ it saw being used in the Mosquito and any spin-offs.

It can only have seen Issigonis’s flat-four as a cuckoo in an overcrowded nest. Development of the flat-four dragged on too long.

In June 1946 it was expected the engine would be in production before mid-’47, yet in April that year there were still concerns about the vibration problem, while the bigger unit for the Oxford still hadn’t made it off the drawing board.

More fundamentally, the Nuffield Organization’s management and Lord Nuffield himself weren’t even sure about bringing the Mosquito to production; its radical design evidently frightened them.

In a maelstrom of decisions and counter-decisions, consideration was given to cancelling the car in favour of an updated Morris Eight Series E, or at best making it in small numbers with an MG badge.

The thought of an all-new flat-four must have had tired managers reaching for the smelling salts. The final blow came in June 1947 at a Morris board meeting.

Citing the arrival of a flat rate of road tax in place of the RAC horsepower system, the flat-four engine programme was abandoned; in October, the Mosquito was at last given the green light and pushed towards an end-of-1948 introduction, ultimately with a conventional in-line sidevalve engine.

Logic, fed by internal pressure from Morris Engines, had prevailed.

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