Keith Adams tells the story of the Rover P7, a series of prototypes to test new engineering solutions for the upcoming P8, as well as planned expansions to the P6.
The story has been updated with amazing new video footage of the anti-roll prototype in action.
Rover P7: the missing link
So, what’s the Rover P7 story? Although the Rover P6 had been launched to ecstatic reviews in late-1963, the main gripe the media had about the car was the lack of refinement from its 1978cc four-cylinder engine. This would have answered that criticism.
Existing Rover models such as the P4 and P5 had smoother six-cylinder engines as, indeed, did the cars from Coventry upstart, Jaguar. More seriously, the Triumph 2000, which was directly aimed at the same market sector as the P6, could also outgun the P6 in the silkiness stakes.
In addition to this problem, Rover faced the more serious conundrum of developing new, lighter engines to replace the 2.6- and 3.0-litre IOE units used in the P4 and P5 saloons. Rover’s Sales Department had wanted the P6 to have a six-cylinder engine from the outset, and so, in 1962 and before the P6’s official launch, Jack Swaine’s Engine Department began to investigate a number of possibilities.
Investigating engine possibilities
The logical thing to do was to build a six-cylinder version of the modern P6 four-cylinder engine. Using the same bore and stroke as the four-cylinder produced a swept volume of 2967cc. The six-cylinder engine certainly produced the required grunt but was 50% longer, which according to James Taylor’s 1996 book Classic Rovers 1946-1986, required a longer nose for the P6 testbeds.
As there was concern about funding of the new engine, a number of Rover P7 prototypes were built using a 2.6-litre version of the old inlet-over-exhaust engine to simulate the 3.0-litre P6-based straight-six. These were designated P6/6 (the full list of P7 prototypes is listed below), but the arrival of the Rover V8 engine negated the need for this developmental direction.
The extended nose from the straight-six resulted in the model receiving a new factory code, P7. However, according to legendary Rover Engineer Spen King in his 2002 interview with Keith Adams, ‘the six-cylinder engine would go into the P6 bodyshell, not just as a P7, which was never considered for production seriously at all.’
Despite that, the P7/4 prototype was capable of 128mph, and its six-cylinder engine was quieter and smoother than the P6 unit. The first three P7s were scrapped but the fourth was sold to Edward Eves, at that time Midland Editor of Autocar (below). He sold it to Ian Glass, an enthusiast in North Wales, who still owns the car.
Spen King on the Rover P7
‘The P7 was purely a development thing. But there was something that we called P7A, which was no longer than the P6 and had the six-cylinder engine in, and double wishbone suspension… To say that it would not go into the car was wrong. In P7, it stuck its nose out and was too heavy and everything,’ he added.
‘It’s not a bad motor car, that engine was a pretty good engine actually. That was too heavy somehow. In other words, if you make a four into a six, you oughtn’t to have to make it 50% heavier because a lot of the stuff there is the same as the four-cylinder. But, in fact, somehow or another, it got a very heavy sump or something, and it made the engine very heavy.
‘I batted very hard against the V8 to try and continue that because I believe the BMW policy was right; if you’ve got something, you ought to develop it – that way you have a linear development programme instead of hopping over here and there – doing something completely different. But I was wrong I think… No doubt that V8 was a huge asset.’
Technical developments on the Rover P7
As well as the various engines fitted, the P7 programme was used to test alternative suspension set-ups. At the front, the P7 received a new double-wishbone front suspension mounted on a subframe. This was isolated from the body by four cylindrical interleaved rubber bushes. Various roll centre heights could be tested thanks to the inner pivot height of the upper wishbone being adjustable. was possible, thus allowing various roll centre heights to be explored.
Later P7s were modified at the rear to incorporate a fixed-length de Dion tube, forward of the wheel centre line. This pivoted on a complex rubber bearing mounted on the axle extension housing. Constant velocity plunging driveshafts were used and diagonal radius rods completed the location. Early assessments were very encouraging with major improvements in ride, handling and road noise reduction.
Rex Marvin, Engineering Manager at Rover, recalled: ‘The usual development programme of spring and damper optimisation, suspension bush rate selection and tyre selection occupied and educated our small team of engineers. A major challenge arrived one day in the form of a 6B pencil sketch by Spen King of an idea for rear suspension levelling using a single Boge Hydromat identical to that which had just been introduced on the low pivot swing axle Mercedes Benz 300 and was later to be used on Range Rover.’
Once built, the system worked well: ‘It provided ride-height correction for increasing payload without adding roll stiffness. The knowledge gained was fed into the Design Office for incorporation in Rover P8.
Rex added: ‘The in vogue handling test at the time was to assess the car’s response to sudden closing of the throttle when on the cornering limit but making no attempt to correct any subsequent deviations. I had done this test dozens of times in the P6BS on the Lucas Proving Ground at Honiley to select a suitable tyre to eliminate the unwanted oversteer.
Testing the Rover P7’s anti-roll suspension
The P7 came close to production
According to James Taylor, the P7A came close to production although Spen King denied this. However, in Taylor’s account, the cost in new body tooling prohibited the final go-ahead. Had the P7A gone into production, it would have been called the Rover 3000 to avoid confusion with the existing Rover 3-Litre. This resulted in the smaller-engined P6 being christened the Rover 2000 instead of Rover 2-Litre.
Instead, in 1964, Chief Engineer Robert Boyle suggested that the company develop a five-cylinder variant of the P6’s 1978cc four-pot. The resulting engine had a swept volume of 2472cc, and presented Rover’s Engineers with the problem of in-car balance.
Spen King’s take on events and the origins of the five-cylinder engine are as follows: ‘I think it came mostly out of Brian Sylvester, who was Head of Research. It was a pretty sensible idea.
Why the five-cylinder didn’t work
‘The problem was that you hadn’t got fuel injection then – you need fuel injection to make five-cylinders work, because the carburetion is a bit of a mess… I mean the obvious way is doing it with an injected version, and this prototype was built with carburettors.’
Fortunately for Rover, the company’s Managing Director, William Martin-Hurst, had stumbled across a discarded light alloy General Motors V8 while on a visit to the USA in 1963.
The engine was compact, powerful, reliable and just what Rover needed. Rover bought the rights to manufacture this engine, cancelled the various P7 projects and was now able to move forwards convincingly.
The V8-engined P5B appeared in 1967 and was followed, in April 1968, by the V8 P6B, now known as the Rover 3500. Could the Range Rover have happened with a 2967cc inline six-cylinder engine?
Rover’s attempt to build a new engine on the cheap was over and a motoring legend was born.
The Rover P7 prototypes tested
According to Rex Marvin’s article posted on Jim Shaw’s Serendipity website, there were several P7s built and tested by Rover’s New Vehicles Development department. You can also see the details of each individual car, as well as Rex Marvin’s hair-raising account of how the P7 was crashed during testing (below), on Jim’s site.
The earliest two Rover P7s (pictured above) were used for cooling tests and, according to Rex Marvin, ‘they presented some tough problems to the young Engineer Jim Randle, later to become Engineering Director at Jaguar. The lessons learnt from these cars were fed into the design of the styled version of the intended six-cylinder car.’
Thanks to: Denis Chick, Jim Shaw, Spen King and Ian Elliott