Opinion : An engine for the Rover P10

Rover P10 engine
Rover P10 engine shows the exhaust manifold design principles re-used on SD1 and Range-Rover V8s. Layout of the auxilliaries, distributor and oil pump drive, give the game away that this engine started life as the P6 SOHC (Picture: Simon Owen)

A few of you will have spotted that, while I love the Rover P6 and enjoy the P5, I am quite fascinated by the Rover that was to come after that: the P8. The initial effort took place after P6 was finalised in 1962, and it centered on completing the Rover range. Rover had always offered a four-cylinder entry-level car: 10 and 12HP, 60, 80. Then three levels of six-cylinder: in pre-war years those were the, 14,16 and 20HP and, in the post-war era, these became the 75, 90 and 105. And later, these changed to become the 95, 100 and 3-Litre and Coupe.

The P6 left Rover with the base four-cylinder and the top of range 3-Litre. Rover needed needed a multi-cylinder P6 to fill the gap. That was the Rover P7, which was powered by the 3.0-litre six-cylinder version of the P6 SOHC engine. Some of these cars were tested even before the launch of the P6. Then, when the Rover V8 engine arrived at Solihull in 1964, everything became much simpler, and the P7 eventually gave way to the Rover P6B.

Thoughts in 1964, therefore, turned to the P5 and P6’s replacement. The first outline specs for the P8 showed it doing both jobs from one body – standard Rover policy throughout the Wilks era – it’s the P5 that is the exception to the rule. Therefore, the P8 was described as having both the 2.0-litre 2000 TC engine and the 3.5-litre ex-Buick V8. Meanwhile, in 1964, the Engine Department’s forward product line already showed the V8 being taken out to 4.4-litres at standard bore, what became the Australian Leyland P76 engine.

Rover P8 was abandoned in 1971, and made way for the Rover P10
Rover P8 was abandoned by BLMC in 1971, leaving its partner, the Rover P10, to soldier on alone…

With the Wilks family aging and getting more inclined to concentrate on larger cars, and David Bache wanting something more American in size and stature, (the USA was then the holy grail export market for all UK manufacturers to crack), the Rover P8 started to grow. The 115bhp Rover P6 2000 TC engine wasn’t going to cut it for the smaller-engined variant.

Relief came, post-merger into BLMC, in the form of ex-Ford man John Barber. He wanted to abandon the high volume sector of the UK market, where BMC went head-to-head with Ford and Vauxhall. He, correctly, reckoned it needed too much investment to keep pace, which only the Americans could afford. So he wanted to do what we now recognise as a BMW-style premium product plan. He wanted to take BLMC upmarket and sell lower volume, higher margin, quality, niche, cars.

This chimed exactly with the strategy of the Wilks family for Rover. So, he commissioned Rover to build a quality and interesting competitor for the forthcoming Ford Granada. That was the Rover P10. Simpler than a full fat Rover (P8), but roughly the same size and with distinctiveness an asset.

Rover P10 proposal

That renewed the interest in the new four-cylinder engine at Rover, to take over from the four-cylinder P6 engine. What was built and ready for production in 1973 has always been a bit mythical… Known to be a 2.2-litre slant four, with the same bore spacing as the P6 SOHC (so that it could be built on the existing engine line) no pictures have ever surfaced.

Until last weekend. It’s on display at Gaydon!

Just LOOK at it!

Its maximum power was 160bhp, from a DOHC 2.2-litre slant-four with 16 valves and throttle body injection. Routine enough now, but revolutionary for a volume car in 1973…

The rest of the tale is rather sad. Barber got the boot for daring to suggest the closure of BMC and the loss of thousands of motor industry jobs in the Midlands to a Labour Government.

A P10 crash testing at MIRA, the last step immediately before production. The number on the door – L69 – tells us that this is the 69th crash test in UK registration year suffix ‘L’ – around Easter 1973. Everything stopped after this to turn P10 into SD1. Note the characteristic tail collapse also typical of SD1

Barber gone, P10 – and Rover – were merged with Triumph and the P10 morphed into the Rover SD1, but not before it got a BMC-quality interior (it looked like the Bache original, but it just wasn’t up to Rover quality levels). The DOHC Rover engine was shelved to placate Triumph, which wanted to use its new six (the PE166 engine) – ultimately, a very bad decision because the six wasn’t up to scratch. We can only speculate as to what V8 the P10 might have got. It could hardly have had the same power output as the four-cylinder motor, which is what the carburetted 3.5-litre that actually went into it delivered. EFi 3.5? Or the 4.0-litre narrow-bore engine destined for P8? Or the (later Australian) 4.4? Or – and here we really are fantasising – a V8 version of the 2.2 slant four…

But perhaps not fantasizing too much… At the time the P38 Range Rover development was under way, there was an active proposal to use an existing 32-valve V8. And that engine was seen by a reliable source at Cowley on an engine stand and was reportedly installed in a number of experimental rear-drive Rover 800s. Of course, 32-valve V8s take a fair bit of designing, so it’s tempting to suppose that, like the crank used in the 4.6-litre P38, it was already on Rover’s shelf from P8/P10 days.

The Designer who did the slant-four went on to spend a couple of days a week at Longbridge. It’s tempting to wonder if that Rover engine led directly to the development of the 2.0-litre 16-valve M-Series engine Austin Rover used in R8 and 800.

The Rover P6, meanwhile, had to soldier on. Instead of leaving the stage gracefully at the October Motor Show in 1973, it received an emergency revamp and ‘value engineering’ exercise to give us the 1974 model year 2200SC and 2200TC. The cylinder boring tools for that DOHC engine were, at least, put to good use!

Thank you to Simon Owen for the pictures of the engine and the wit to photograph it!

Chris York
Latest posts by Chris York (see all)


  1. Thank you for this, but I take issue with a three of points in this article.

    1: “The DOHC Rover engine was shelved to placate Triumph, which wanted to use its new six”

    I think the reality was more of necessity, the business did not have the money to tool up a another 4 cylinder engine line (they had the O Series and Slant 4 – how many 4 cylinder engines does a company need) and the closure of the 6 cylinder line at Canley would have caused massive industrial relations issues. It is why Rover/Triumph decided also not to simply build a 6 cylinder Slant 4 (Slant 6) or use the E6, it was simply involve too many days of lost production to justify the investment.

    2: “so it’s tempting to suppose that, like the crank used in the 4.6-litre P38, it was already on Rover’s shelf from P8/P10 days.”

    Tempting but not reality, Rover’s strategy under BAe to replace the Buick engine was a V8 K series derivative, an extension of the V6 K series which came conveniently with a 90 degree spacing. However these plans I believe never got as far as a running engine, although they were mocked up in the metal (as was a 3 cylinder for the Mini using a single V6 head and cut and welded 4 cylinder block) and I recall at the time of the Phoenix collapse seeing one on the shelving in the Flight Shed at Longbridge.

    3: Tempting to wonder if that Rover engine led directly to the development of the 2.0-litre 16-valve M – Series engine Austin Rovers used in R8 and 800.

    Again tempting but not reality, Spen King says (As Director of Engineering at the time he would know I guess) that the start point for the M Series combustion chamber, valve angle and tract was the Slant 4 16v sprint engine (interestingly a former Saab powertrain engineer I met at the Saab Museum at Trollhättan also says their 16v engine twin cam evolution of the slant 4 also had the Sprint Engine as there start point).

    • I broadly agree with you here. But you are talking from the perspective of the successors of BL/BMC, where I have been speculating on events at the remnants of the Wilks family Rover Company.

      On point 1. Absolutely correct! But remember that this “P10” engine didn’t need a new engine line – it was to be built on the existing Rover 2000 P6 engine line.

      On point 2. Except that you are talking about a much later period. It is easy to forget just how distant from later events the genesis of P8 and P10 are. I am persuaded that the very private source describing to me that quad cam V8 is reliable and accurate. Which does beg the question as to what the engine actually was. The K V8 is clearly a candidate, but it might be a tad early? So too would be a Sprint headed 3 litre Stag. (What ex Triumph engineer would be able to resist trying that, if only unoffically!). And yes, that would appear to be missing a couple of cams… Maybe SAAB heads?

      On point 3. Yes. Quite correct! But that actually doesn’t preclude the head being Rover derived/inspired, just using the best available elements found elsewhere in the Group. The key point for me is the presence of that Rover engineer who had done the P10 engine as it was being developed.

  2. Seem to recall detuned versions of the 2.2 P10 unit putting out about 120 hp at minimum for an entry-level version, with an unbuilt 2.8-litre version of the Rover V8 being considered for the Rover P10 at one point called Project Redcap as a companion engine to the 4-cylinder engines (which would have been a plus in the German market that penalized engines above 2.8-litres such as the larger 3.5 Rover V8).

    Have read of the 2.2 P10 unit putting out as much as 168-170-ish hp, had it been produced would not be surprised if Rover soon developed a reduced-bore 2-litre version of the P10 engine for the Italian or other markets where cars displacing more than 2-litres were heavily taxed.

    Given the output of the 4.4-litre Rover V8 in the P76, have been of the view that in better circumstances a 32-valve quad-cam V8 version of the P10 Slant-4 would have eventually replaced the Rover V8 in the Rover P8 and P9 (to effectively challenge the likes of Mercedes in the case of the P8) thereby having a single engine family to replace both the P6 OHC and the Rover V8. IIRC seem to remember an old thread on one of the Rover forums discussing this very subject.

    Am more curious about the P10 engine’s ability to form the basis of 5/6-cylinder engines as was the case with the P6 OHC-derived 5/6-cylinder experimental engines used in the P7 prototypes, which in the hypothetical 5-cylinder P10 engine’s case would not have been held back by the lack of fuel-injected like the 5-cylinder P7 engine was (or held back due to weight like the 6-cylinder P7 engine due to the P10 engine reputedly being much lighter as a result of being all-alloy).

    The same could be said with regard to the P10 engine’s potential to be dieselized since seem to recall James Taylor’s Land Rover books mentioning 2.2-litre Slant-4 petrols and diesels being considered for replacement projects like Adventurer, though it is not clarifying whether they were derived from the Rover V8 or a remnant of the P10 Slant-Four (or P6) engines.

  3. In 1973 why waste time, effort and valuable cash and resource on this when they had the Triumph slant 4 – with a 16V head ready to go? Internal politics the scourge of British Industry and commerce then as now!

    • Am reading it as the P10 engine originally being developed prior yet ready for production by 1973.

      Would agree on the potential overlap with the Triumph Slant-Four, yet the latter was costed down by BL to the point of not realizing its true potential (along with the Triumph V8) and later prompting Triumph to consider developing a 4-cylinder version of the PE166 as a potential successor to the Slant-Four.

      There is also the fact that while Triumph engineers were able to extract a 150 hp from test engines, the production line was unable to build them to the same level of quality leading to production outputs ranging from 125 hp to 130 hp. Sure, it is possible that Rover would be in the same situation with the P10 engine though they had a fairly decent reputation with the P6 engine (along with quality) prior to acquiring the rights to produce the 215 Buick V8.

      Am more interested in finding out about the P10 engine’s torque figures to compare it to other near contemporary or later Slant-4 engine designs from Triumph, Saab, Vauxhall, Lotus (e.g. “Torqueless Wonder”), Volvo (e.g. Redblock), Porsche (e.g. later 924, 944, etc) and possibly BMW (e.g. M10), etc.

      • The production PE sixes being rated at 136DIN ( 2.6 ) was nothing to do with poor quality, but was a conscious decision to lower the state of tune so that the 2.6 did not compete directly with the 3.5, which was rated in carburetter form at only 155 DIN

  4. Paul… “Internal Politics”… Nowhere near as the more harmful scourge of the “External” version by those we entrust the Nation’s well being every few years or so, particularly where indigenous UK Industry is involved..

    Talk about not fit for purpose. Ongoing to this very minute. I have SKY News 24/7/365 running as I type this.

    No end to their bovine excrement.

  5. Slightly confused by the timelines here. That crash test photo in 1973 suggests that the P10 project had progressed VERY significantly before turning into SD1, whereas I’d always thought that P10 won against the Triumph proposal much earlier, and that by 1973 it was very much the joint Rover/Triumph SD1 being developed?

  6. Aside from the engine, the thing that interests me is the tail collapse under frontal impact. Can any clever people tell me the technical/structural reasons for it?

    • It occurs, because on impact the rear wheels leave the ground and then on recoil the car bounces back onto those wheels and with some considerable force slams down on its rear suspension bump stops.. In the P10/Sd1 the you have a relatively long and soft tail (leverage and low strength) below a large heavy tailgate, which thus deforms the rear structure.

      • Ah I see, it’s as a result of the wheels leaving the ground and the lack of strength in the structure. Cheers

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