Jensen SP | The Inside Story
The new Jensen SP, with its Six-Pack carburettor system, was launched to market in 1971, as the Company’s new flagship car. The car was plagued with carburation problems from the outset, leaving many loyal Jensen owners frustrated and disenchanted.
With help from various former employees, the Museum looks at the inside story of the Jensen SP – a car that has taken nearly half a century to find its right market.
Jensen SP | The Inside Story | Background
With the Jensen FF being phased out, the boardroom discussion moved to a replacement flagship model. Something was urgently needed as a flagship model, to bridge the gap between the Jensen FF, and the all new Jensen ‘F’ Type, which the boardroom were hoping would be going into production during 1973.
According to former Sales Manager, Tony Marshall, this new flagship car had to be achieved on a ‘quick & dirty’ basis. In other words, something that wouldn’t take any development time, and would require a minimal budget.
Jensen SP | The Inside Story | Boardroom Decisions
Marshall remembers that the boardroom flagship car debate took place in summer of 1970. Those present were, himself, Alfred Vickers, Richard Graves, Kevin Beattie, and David Millard.
Based on requiring a flagship model on a budget with minimal development, the narrative moved to an Interceptor-based model, possibly with a different engine, such as a Hemi.
The discussion was positive, and it was agreed by all present that the Chrysler rep would be contacted to see what alternatives Jensen Motors could look at in respect to engines.
The Chrysler rep was contacted, and it was mentioned that Jensen Motors were looking for some sort of performance engine, which they could brand up to supersede the FF.
The rep mentioned that Chrysler had a small batch of Six-Pack performance engines. Since Chrysler were going to have trouble selling them in the US market, due to new emission legislation coming in, he believed they would be more than happy to supply Jensen Motors with them – and probably at a very good price.
Within days, an agreement had been reached, and Jensen Motors pledged to acquire the remaining batch of Six-Pack engines, which had been sitting gathering dust in a Chrysler warehouse in Canada.
With the engine agreed, the boardroom discussion resumed. For marketing a new flagship car, it needed to stand out from the standard Interceptor, so the discussion moved on to other ways of making the new model stand out.
A vinyl roof as a standard feature was also proposed and accepted. In terms of on-board entertainment, a particularly high quality, high value Learjet ‘8’ track system was put forward as another standard feature, instead of the Radiomobile units, which had been fitted previously.
Marshall mentioned that a fully louvred bonnet would be a great style feature for the car, and not only would look good, but would harp back to traditional British racing cars of years gone past.
Everyone around the table thought it a great idea, and the discussion ended with everyone agreeing the SP should be badged up in blue instead of red, to carry on from the FF as a flagship colour.
A suitable model name was also needed, and although no one person can be credited for the model name ‘SP’, it was an obvious choice, that more than one person at the table had brought up.
Jensen SP | The Inside Story | Into Production
From the point the boardroom decision on a new model called the Jensen SP was agreed, things happened quickly. In December 1970, a production Interceptor II painted in a new colour – reef blue- was taken off the track and given over to Engineering.
The chassis used, was number 123/3917, and the first job was to fit one of the Chrysler 440 Six-Pack engines, ready for the car to be tested. The car was also fitted with dial-up speed control, which was tested as a possible production fitting.
However, according to former mechanic, Richard Peckover, from the Engineering Department, some initial SP testing actually took place earlier, in September / October of that year. This testing was carried out using a customer’s car. Interceptor 123/3889 was ordered by the customer to have a 440 Magnum engine fitted as a special order. Peckover tells us more,
“The engine was prepared in Engineering, and an SP carburation system fitted. The unit was then fitted by Production, but not fired up at end of line. The car was delivered back to Engineering in the normal EOL condition, with slave seats, wheels, bumpers, along with floor mounted tachograph, speedometer.
We then undertook initial start and preliminary testing. I did all the down testing and snagging. We worked on this vehicle for a couple of weeks, and in fact, myself and Jonathan Haynes, did the initial SP performance tests at MIRA using this vehicle. Afterwards, the car was returned to production for the removal of the slave parts and finalisation, ready for the car to go to Sales.”
Peckover’s memory is that the Six-Pack carburation system remained on the engine when the 123/3889 left Engineering. We do not know if a standard carburation system was fitted back in place, after the car went over to Production, for removal of slave parts and finalisation.
With 123/3889 out of the hands of Engineering, it was over to 123/3917 to take over as the SP development vehicle. With a well set-up SP engine under the bonnet, this (and obviously 123/3889) was one of the fastest cars – if not the fastest – trialled by Engineering.
It was clear those testing the car, were taking it to its limits, as on more than one occasion, 123/3917 ended up in the repair shop. This development car would carry on to serve as the mechanical platform for the Jensen ‘F’ Type project, by which time it was known as ‘Big Bertha’ (on account of its widened arches).
All in all, work to develop the Jensen SP ready for production to begin, was straight-forward – which was exactly what the boardroom wanted. One small issue was a clearance problem.
It transpired the SP set-up stood slightly higher than the engine with Carter, and there was a point where the bonnet and the slightly domed SP air-filter could foul each other. The problem was a relatively quick fix. A circular template was made, which would be pressed into the centre of the Chrysler air-filter lid.
The new Jensen SP was given two factory schedule numbers, 131 for the RHD Jensen SP, and 132 for the LHD Jensen SP. These would change at the end of 1972, when various revisions were made both to the Interceptor III, and SP. The later schedules were 134 for LHD Jensen SP, and 138 for the RHD Jensen SP.
With the SP concept tried and tested, two of the new MK.III chassis were given over for build up as SPs. The two cars, bearing the new prefix ‘131’ were to be made ready for the 1971 Motor Show.
Chassis number 131/4254 (assigned the registration number ‘GEA 77K’), and chassis number 131/4261 (assigned the registration number ‘GEA 88K’), were hurried through production, and finished in September 1971, ready for the 1971 Motor Show.
131/4254 was built up with a specification of tangerine with black trim, and black vinyl roof. This car would be on the Jensen stand. Meanwhile 131/4261 was built up with a specification of yellow with black trim, and with a black vinyl roof. This car was waiting outside the Motor Show for demonstration purposes.
Jensen SP | The Inside Story | Release To Market
Initially, Jensen Motors had started their marketing stating that for October 1971, they were bringing out three new models, the Interceptor MK.III, the Jensen SP, and the Jensen FF MK.III.
However, they quickly realised this would be sending out mixed signals. The whole idea behind the SP, was for it to take over from the FF as the new flagship car.
Over and above that, the FF MK.III was simply a way of the Company finishing off the remaining FF MK.II shells as MK.IIIs, and capitalising on the make-over. There was only ever going to be a handful of the FF MK.III cars, and these would undoubtedly be quickly bought up by existing FF owners of earlier models.
So, marketing of the FF MK.III was curtailed in favour of the Interceptor MK.III and the SP. Hence, when the main marketing for the motoring press , and for Jensen distributors / dealers took place in the lead up to the motor show, the FF MK.III was no where to be seen, and barely mentioned.
A preview of the new Jensen SP took place in advance of the 1971 Motor Show. Good Relations had secured the Sonesta Tower Hotel for the 30th September. Three cars would be shown to the motoring press, along with Jensen distributors and Jensen dealers.
The three cars included an Interceptor III in LHD federal compliance form. A RHD Interceptor III, and the Jensen SP. The new Jensen SP was priced at £6,976.87 including Purchase Tax, just under a thousand pounds more expensive than the basic MK.III Interceptor.
The motoring press would get the first showing, and then later in the day would be the turn of the Jensen distributors and dealers. Edgar Schwyn, the ‘Go-Get’ swiss Jensen distributor, wasn’t going to miss the chance to get a first glimpse of the SP.
Schwyn arranged a visit to England for himself, his swiss dealers, and all their wives. The trip included the obligatory tour of the Jensen factory (one of many that Schwyn had done), and then down to London to take part in the distributor & dealer viewing of the new models at the Sonesta Tower.
Typical of Schwyn, he was keen to get his hands on one of the SPs, and had already mentioned to both Tony Marshall, and Richard Graves, that he would like a LHD SP made ready for the Geneva Motor Show of March 1972.
Jensen SP | The Inside Story | Media Attention
The new Jensen flagship was received with moderate interest by the motoring press. The SP was of course a far cry from something like the revolutionary Jensen FF, which it was superseding.
However, after testing, the press were excited enough with the performance. Both Motor & Autocar had their chance to test-drive the new Jensen SP at the back-end of 1971. Both drivers managed to propel the SP up to 140 mph top speed, and a tad beyond (Autocar achieving 143).
Autocar was the first to test the new Jensen SP. They were given chassis 131/4254 to road test during September 1971, and the car was taken over to the Continent and driven across to Switzerland and back. The review came out in the 7th October 1971 issue.
It came across as a cautious review. The drivers enjoyed the overall performance of the car, but with a whole host of caveats about the engine.
The review started,
“AT-A-GLANCE: Six-pack Chrysler 440 engine gives terrific punch at full throttle, but lacks medium throttle response. Very good steering and stability; ride fair. Brakes generally very good, but a little rough from high speed. Moderately priced in its class, and a very practical 120 mph cruising grand tourer.”
Mention was made of the issues surrounding the extra carburettors kicking in when the driver wasn’t expecting it. There was also various issues with their test car in respect of pinking, and even after the car was returned to Jensen Motors and a new distributor fitted – the pinking returned. The other issue was starting from hot,
“The engine is slow to fire when hot, and the seemingly endless churning on the starter motor spoils the illusion a little for onlookers admiring the car. The best technique was to open the throttle a little way, keep it there while turning, and promptly releasing the ignition key. Often this would give a second or third time start, otherwise one has to resort to the technique of giving full throttle and turning the the key until the engine fires, which it never failed to do after about 5-10 seconds.”
There was even a less than positive feedback on the multi-louvred bonnet,
“To cope with the considerably higher heat output of the the bigger engine, the bonnet louvres play an important part in helping to keep the under-bonnet temperatures down; they also look fine from the driving seat, but the effect is slightly spoilt by the tendency for the bonnet to slightly shiver, almost as though improperly fastened.”
When all was said and done, it was a lacklustre review, and management at Jensen Motors must have winced when they read it.
Motor released their test of the SP in their 18th March 1972 issue. At least this review was more upbeat, although caveats surrounding the Six-Pack operation persisted,
“The term sports car used to be fairly clear cut – two seats and wind in the hair – but now it embraces the GT brigade, still largely two seaters, or at best two plus twos; yet nobody would really think of a Jensen as a sports car. With its distinct boardroom appeal it isn’t, but there are few of the genuine article which can keep up with the Jensen SP either in a straight line or through the twisty bits.”
Motor’s feature on the new Jensen SP was generally enthusiastic, and the drivers obviously enjoyed their experience of the car. However, as much as they enjoyed the ample power and acceleration of the SP, they quickly went on to outline drawbacks with the six-pack system,
“The operation of the Six-Pack system isn’t entirely satisfactory; most of the time you will probably be entirely content to accelerate away, albeit still quickly, on part throttle which means just one carburettor until about 110 mph. The extra four chokes come in according to throttle position and engine load – a pressure compound system rather than mechanical.
You soon know when they come in as the engine, which is hardy audible on part throttle, begins to emit a purposeful roar and you receive a firm push in the back.
This sounds simple enough, but there are two side effects; one is that response to sudden demand for acceleration when cruising is a bit slow as the torque converter winds up and the carburettors gulp air to compensate for the powerful accelerator pumps; it pays to select the lower gear manually.
This is all relative but when you get used to the potential acceleration you expect response to match – driven intelligently the Jensen can be very quick through traffic. The seconds effect is more obtrusive.
With the extra chokes coming in with increase in engine load you can get sudden excess of power with no noticeable throttle movement. This can happen when cruising at 110 mph and you start to climb a slight hill; the extra load on the engine is enough to open the chokes and it won’t slow down until 130 mph unless you lift off first, in which case the shut-off is rather sudden.
It can also happen when rounding a corner on constant throttle and the extra load provoked from tyre scrub etc can open the chokes in mid-corner which will be enough to dislodge the tail.”
This is exactly what happened to Andrew Bee, head of the Quality Engineering Department at Jensen Motors,
“I was test driving an SP, and took the car into a corner on a constant throttle, suddenly the chokes opened and there was a sudden gush of acceleration. It was momentarily disconcerting, as I wasn’t trying to make this happen. Luckily it didn’t end in an accident.”
A further review of the Jensen SP appeared in the Australian magazine, Sports Car Road Tests (issue 9). They tested the first Jensen SP imported to Australia in early 1972. The mustard coloured SP was chassis 131/4472.
At last, the SP received a praiseworthy review, entitled ‘Booming Jensen SP’. The review starts,
“If the Jensen SP can be summed up in one word, then that word unquestionably is “relentless”. This big, beautiful car seems to flatten hills, ignore bends, smooth out bumps and just keeps pounding on and on.
Driving it is rather like being in a jet aircraft with a remote hum of expensive machinery somewhere beyond you, and when a stretch of bad road passes below your wheels, the effect is exactly like a plane hitting bumpy air or flying through a rain cloud.”
It was obvious that the drivers of the first Jensen SP in Australia, thoroughly enjoyed their experience. They also managed to get some pretty good maximum speeds out of 131/4472. Fastest run at 147 mph, average of all runs at 144 mph. Speedometer indication on fastest run at 151 mph. The Jensen SP was priced at Aus $ 25,900 on release in 1972.
Jensen SP | The Inside Story | Mechanical Nightmares
Some Jensen FF owners purchased the Jensen SP, simply because it was marketed as the new flagship model, taking over from the Jensen FF. And many Interceptor owners traded up to the Jensen SP, believing they were buying the best that Jensen Motors had to offer. Unfortunately many buyers of the SP were less than pleased with their choice of new car.
The SP engine was temperamental, and could quickly go out of tune. To add salt to the wounds, the majority of buyers of the new flagship gentleman’s express, had little or no mechanical knowledge, and that didn’t fair good with an engine like a Chrysler Six-Pack.
According to Tony Marshall, to make matters worse, most Jensen distributors didn’t have mechanics trained properly to service and tune the Six-Pack engine.
Quality Engineer, Paul Turner, remembers the continuous issues with the SP,
“The car was fast becoming the Company’s ‘Titanic’ rather than ‘Flagship’. Even from new, the SP carburation system as fitted to the ‘g’ series engine was playing up.
The electronic system which had been fitted to the first cars was not reliable, and had a tendency to cut out. As such standard distributors with points were fitted. A more reliable electronic system was found, and fitted not long after production started.”
I spent a lot of time modifying the distributor curve, which improved the running of the engine. This at least made the cars good to go to sale, but that was just the start of the issues once the customers were driving them around.”
Jensen SP | The Inside Story | Enter Dudley Gershon
The likes of Paul Turner, from Andrew Bee’s, Quality Engineer Department, had achieved some good basic ground work with the SP engine. At least the SP engines ran to an acceptable level – acceptable enough to have the cars drive-worthy to go to sales.
However, Turner knew this was just the beginning of a much bigger problem. He recognised that once these cars had been sold on to customers, the problems would return. And it didn’t take long. Within months, cars were being taken back to distributors, and to Jensen Motors, for all manner of poor running issues.
John Page, a part of the Technical Service team, was charged with looking into the overall issues of the SP, and to come up with solutions. Page takes up the story,
” Unlike the American cars using the Six-Pack, the Jensen SP produced a huge amount of under bonnet heat. This was down to the large amount of room within the engine-bay on the American cars, and the very limited room on the Jensen.
This extreme of under bonnet heat caused all sorts of issues with the carburettors. Parts of the carburettors would warp and contract due to extremes of heat and cold.
This led to air gaps, and the SP set-up being impossible to adjust for a correct idle. But that was just the start, there was also many reports of erratic slow running at curb idle.
Additionally, other issues included detonation on light throttle at about 2000 rpm, and flat spots in carburation. Although we managed to get over some of these issues by putting modified springs in the distributor.
Another series of problems we were facing from customers cars, was the fact that due to the nature of the SP carburettors, they ended running too rich after a week of being driven around.
How was a customer supposed to contend with that ? The fact was, these were basically performance engines, not something for a company director to use around town.
The situation became so serious, that in February 1973, Jensen Motors brought in Dudley Gershon, Aston Martin’s Director of Engineering, as a consultant. While Gershon was at Jensen Motors trying to come up with a sensible solution to the SP problem, I worked directly under him.
We spent weeks trying to come up with a long-term solution, that would make the car generally reliable for our customers. We tried various float fixings. Different gaskets under the carbs. Other heat shield devises.
Often we would get the whole carburettor set-up right, send the car out, and it would be back a week later just as bad as when it first came in.
Oh ! and this was just the start. Some customers were very unhappy about the outboard carbs (which were vacuum operated via the centre carb), cutting in, causing the car to accelerate suddenly.
It was something Jensen Motors were worried about, as we could all see the possibility of accidents happening, and Jensen Motors being held responsible. Just imagine us being taken to court, and the negative press that could emanate from the case.
In the end we came up with a solution. Change the entire Six-Pack set-up, and fit Carter Thermoquads. That alleviated the problem.”
Many Jensen SP owners felt obliged to have their car’s Six-Pack carburettors removed, and a Thermoquad fitted, in the hope of ending up with a more reliable and satisfactory car. A case in point was the Devon-based businessman, McKenzie-Coles.
Having previously purchased Aston Martins, he bought his first Interceptor in the late 1960s, and then traded the Interceptor for the more SP in late 1972. The car underwent numerous breakdowns in the first year, before – in desperation – McKenzie-Coles had the car transported up to West Bromwich in the hope that Jensen Motors could alleviate the problems.
By this time, Gershon and Page had settled on a change of carburation, to the more sedate & reliable Thermoquad. McKenzie-Coles car was fitted with a Thermoquad, returned to it owner, and certainly ran better. However, the magic was gone, and the car was sold off in 1974.
For Jensen Motors, the Gershon – Page solution was a bitter pill. Here was the Company’s new flagship car, pitched with this amazing engine, sporting this glorious array of carburettors. How could they sell a new SP without the Six-Pack carburettors.
The reality was they couldn’t. As such, new SPs continued to come off the line, sporting their Six-Packs, and were duly sent off to the distributors.
The Gershon – Page solution was positioned to come in later – i.e. when a distributor came bleating to Jensen Motors, that their customer was fed up with their SP constantly breaking down.
Its believed that something like 25-30% of all SPs had their Six-Pack carburation systems changed for Thermoquads, either at distributors, or at Jensen Motors.
From day one, Jensen Motors knew the SP was going to have a short life. Chrysler were not going to continue manufacture of the Six-Pack engine, and by the time Jensen Motors had shown interest, the engine was no longer in production. Jensen Motors purchased most of the remaining engines, and had built 208 Jensen SP cars by the time they had run out of SP units.
All in all, no one at Jensen Motors was that unhappy when the supply of engines had run out, necessitating the demise of the SP.
With development issues continuing with the ‘F’ Type, it was the Jensen Convertible that had to step in during 1974 as a sort of flagship car for the Company. As Good Relations Chairman, Tony Good, was later to state,
“The Jensen SP was just about the worst case of pitching the wrong product to the market it was intended for.”
There is little doubt the Jensen SP would have been a magnificent car at the time, had it been pitched to a niche market of high performance car drivers with a strong background in mechanical engineering.
However, the car’s shortcomings (in regard to the market it was presented to) had never really hit the motoring press, outside of muted discussion of Six-Pack foibles. The Company had been very lucky indeed, and running out of engines, and discontinuing the SP had probably been timely.
It has taken nearly fifty years for most Jensen SP cars to end up in the hands of drivers with a strong background in mechanical engineering, that are used to driving high performance cars.
Or in many cases, wealthy collectors of classic cars, that often have their own professional mechanics to look after their collection. And the last thing today’s owner wants on their SP, is a Thermoquad Carburettor. They will hunt the globe for an original Six-Pack carburation system, to be re-instated to their SP.
The Jensen SP may have been a ‘quick & dirty’ flagship for Jensen Motors, but it has left a lasting legacy. It brought that wonderful Chrysler Six-Pack unit , packaged in the Interceptor body, to Great Britain. And today it is something to enjoy and behold.
At last, it is a case of the ‘right’ car for the ‘right’ market.
Jensen SP | The Inside Story
ACKNOWLEDGEMENTS: Andrew Bee, former Head Quality Engineering Department | Brian Berkin, Jensen SP specialist | Tony Good OBE, former Chairman, Good Relations | Han Kamp, Jensen historian | Felix Kistler, Secretary, Swiss Jensen Owners’ Club | Tony Marshall, former Sales Manager, Jensen Motors | John Page, former Technical Service Team, Jensen Motors | Richard Peckover, former Development Engineer, Jensen Motors | Paul Turner, former Quality Engineer, Jensen Motors | Duncan Watts, Mopar specialist
COPYRIGHTS: The Jensen Museum | Felix Kistler, Secretary, Swiss Jensen Owners’ Club | John Page, former Technical service Team, Jensen Motors
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