From quite an early stage, it had been apparent that one of the Triumph 2000’s limiting factors would be its top-end performance. Although more than adequate at the time of its launch, by the mid-1960s the 90bhp offered by the 1998cc engine was beginning to be seen as a limiting factor on sales, especially once Rover announced its own 2000TC model in early 1966. Mechanically, the Rover 2000TC was considerably uprated compared to the original P6 and this showed with a top speed of nearly 110mph and a 0-60 time of less than 12 seconds, further increasing the performance advantage of the Solihull product over Triumph’s 2000. Whilst the Triumph still excelled in terms of flexibility, refinement and economy, the 2000TC’s newfound power and speed appealed strongly to a substantial number of potential buyers, and Rover’s marketing exploited this to good effect.
With this, and the knowledge that Rover was working towards the eventual introduction of a V8-engined P6 derivative, the pressure upon Triumph to respond with an up-gunned 2000 of its own increased markedly. Although the works rally cars had demonstrated beyond doubt that output could be considerably increased, their peaky and noisy (not to mention thirsty) triple-carburettor engines were not a viable proposition for a road-going saloon car, even in watered-down form, as the abortive 2000TS package had demonstrated. New engines (including an overhead-cam V8) were in the development pipeline, but readiness for production remained some considerable way off. Unfortunately, although part of the increasingly-large Leyland group, Triumph’s in-house design and development resources were still limited by the industry standards, and this frequently restricted effort to only the most pressing requirements. In the mid-1960s, whilst Triumph’s engineers and marketers must have been concerned about the competitive threat to their big saloon posed by the Rover 2000TC, they were even more worried about the future of the fast-selling TR4 sports car, the Standard Vanguard-based four-cylinder engine of which was looking increasingly incapable of meeting performance and legislative demands in the company’s biggest export market, the United States.
As early as 1965, moves had been made towards grafting the 2-litre six-cylinder engine into the TR chassis but, at first, results were unpromising. All this changed when an engine was equipped with Lucas petrol injection, first as a straightforward power-boosting exercise for competition purposes but then as a possible means of complying with the reduced exhaust emission levels which would be required in order to keep selling cars into the American market in the 1970s whilst retaining some semblance of performance and economy. Although the idea of petrol-injected cars for the US would lose favour after Triumph’s importers there indicated their reluctance to accept the cost burdens associated with the new technology, PI-equipped engines had another important attribute and, for TRs sold outside the US, this was to prove decisive. As Jaguar had discovered with its sports-racing D-Types a decade earlier, the flexibility (not to mention economy) of a PI-equipped engine could be significantly increased over that from a comparable carburetted unit, even with a racing-style ‘wild’ cam profile. So-equipped, the six-cylinder Triumph engine could be made to produce the sort of power outputs only previously seen from the works rally cars, whilst retaining sufficient tractability for everyday road use. The one key aspect in which the prototype 2-litre PI units were deemed to compare unfavourably with the old four-cylinder TR engine was in terms of bottom-end torque, and so swept capacity was boosted to 2498cc by increasing crankshaft throw and piston stroke. As launched in the Triumph TR5 in October 1967, the latest version of the straight-six was claimed capable of a power output of 150bhp at 5,500rpm and torque of 164lb/ft at 3,500rpm, representing considerable gains on the parent 2000 engine (though North American customers would have to make do with a specially carburetted ‘emissions control’ version – the TR250 – which was nowhere near as potent).
With the 2000 in need of a similar boost in power, translating the new engine to the saloon range as well was an entirely logical (not to say predictable) move. By the time of the TR5’s unveiling, development work in adapting the 2.5-litre engine to the 2000 was already well underway, and the result was announced as the Triumph 2.5PI in October 1968. Although the gestation process had proved somewhat longer than had been expected, much detail work being necessary to adapt the highly-tuned TR5 engine to the requirements of a luxury saloon, the year’s timelag between the launching of the two cars allowed Triumph to gain some useful service experience from the sports car which could be beneficially applied to the saloon installation. Compared with the existing 2000 engine, the 2.5PI unit boasted a stiffened cylinder block, a new full-width head offering better gas flow and more reliable clamping of the head gasket, a 9.5:1 compression ratio, altered valve events and a duplex timing chain. The heart of the Lucas PI system was a combined metering and distribution unit mounted adjacent to the ignition distributor and which was of the new Mk2 variety, preserving the tried-and-tested method of fuel delivery via concentric piston and rotary sleeve valves, albeit in a form which was both refined and simplified compared with earlier iterations. As with previous sports car applications of the system, mixture richness was governed by a vacuum control unit which determined fuelling on the basis of engine load. Six sequentially-operating injectors were mounted in triple inlet manifolds providing individual butterfly-valved inlet tracts for each cylinder, fuel being delivered from a high-pressure gear-type electric pump mounted adjacent to the petrol tank. To compensate for the increased load on the electrical system imposed by the fuel pump, the dynamo was replaced by an alternator. Generally similar to that in the TR5, the saloon version of the engine had nevertheless been slightly detuned in order to maximise flexibility and refinement, a less radical camshaft profile (shared with the contemporary Spitfire and GT6 engines), recalibrated fuel metering unit and single-pipe exhaust giving a marginally lower stated power output of 132bhp at 5,500rpm but one which was allied to a much wider spread of torque (153 lb/ft at 2000rpm).
To handle the extra power of the 2.5 engine, gearbox and overdrive units were mildly uprated from 2000 specifications, combined with the same 3.45:1 final drive ratio as on the TR5 in the interests of speed and economy. Suspension settings remained largely unchanged from the 2000, though the new 2.5PI did gain an uprated brake servo and thicker front discs, along with 185-section radial-ply tyres. The horizontal spare wheel stowage was standardised, the raised boot floorboards allowing the high-pressure electric fuel pump assembly to be securely located away from luggage, beside the spare wheel itself, whilst remaining conveniently accessible for routine maintenance. Cosmetically, there were no sheet-metal changes, the new car being distinguished chiefly by new badging, vinyl-clad rear pillars and Rostyle wheel trims. Few interior modifications of note were made, though a sports steering wheel was made standard, along with two-speed windscreen wipers. This styling restraint was as much dictated by financial considerations as aesthetic ones (as was the absence of the competition-inspired limited-slip differential and rear disc brakes anticipated by some journalists), but the result was a car of elegant yet happily understated appearance.
Despite vying for attention with a number of other significant newcomers such as the Ford Escort, Jaguar XJ6 and Rover Three-Thousand-Five, the 2.5PI made quite an impact in publicity terms and, if Triumph had high expectations for press and public reaction to its new model, the company cannot have been greatly disappointed. Autocar sampled a 2.5PI and reported a top speed of 106mph and 0-60 time of just over 10 seconds, allied to a typical fuel consumption of 25mpg. Although some criticisms were voiced over the weight and responsiveness of the PI’s steering, the overall response of the magazine bordered on the ecstatic, praising the car’s easy yet exhilarating performance, surefooted handling and ‘near perfect’ brakes. Motor was similarly welcoming, citing a dramatic improvement in performance over the Triumph 2000, and opining that this, combined with its still-modest pricing, would make the 2.5PI a formidable competitor in the emerging market for high-speed family saloons. For its part, Car magazine provided the inevitable detailed comparison between the PI and the Rover P6, finding that although the Rover 2000TC enjoyed a slightly higher top speed, the Triumph proved consistently more flexible and provided much better acceleration, resulting in a perceptibly quicker car for everyday driving. The Triumph’s accommodation was also judged superior to that of the Rover, as were its abilities as a relaxed high-speed cruiser, though the handling of the Rover – in four-cylinder if not V8 format – was still reckoned to be marginally superior. Overall, however, the magazine found the two cars to be very closely matched.
In addition to providing Triumph with a viable response to key competitive products, both at home and abroad, the adoption of petrol injection for volume production cars was a definite ‘first’ for a British manufacturer. Prior to the introduction of the TR5 and 2.5PI, the availability of fuel-injected cars on the UK market had been restricted to a small number of imported models from manufacturers such as Lancia, Mercedes-Benz and Volvo, and most of those in the higher price brackets. By joining what was still seen as a rather exclusive club, Triumph could quite justifiably claim considerable kudos and was not slow to exploit this in its press advertising, encouraging prospective buyers of the 2.5PI to ‘Join the Power Elite’. Both Jaguar and Rover had been experimenting with various fuel injection set-ups for production cars, but neither would proceed at that time due to supply issues, which also caused Aston Martin to withdraw an injected version of its own straight six after only a short while in production. One particularly significant customer group to appreciate the big Triumph’s new-found power would be the Police; the 2000 was already fairly well-established as a patrol car, and several forces had been experimenting with uprated cars in various levels of tune as potential replacements for the Jaguar 3.8 Mk2 and S-Type models which were then nearing the end of production. The 2.5PI offered similar if not better top-end performance than could be obtained from ‘go-faster’ 2000s and with far greater versatility as well, not least in terms of its phenomenal mid-range acceleration, and before long the type would become a popular choice for motorway patrol duties in particular.
Initially, only a saloon version of the 2.5PI was released, in both manual and automatic-gearbox forms, the latter a definite one-up over the Rover 2000TC on which automatic transmission could not be obtained at any price, though Rover devotees could opt for the rather more expensive V8-engined Three-Thousand-Five, then available only in two-pedal format. Despite the inevitable price premium over the Triumph 2000, early sales of the 2.5PI were sufficient to underwrite healthy production volumes, and an estate car derivative was added to the mix early in 1969. Most export markets already receiving the 2000 were also offered the 2.5PI, though no attempt was made to use the type to revive the flagging fortunes of the big Triumph saloon in the United States, British Leyland’s subsidiary there already having made the decision to concentrate on promoting Triumph as a sports car specialist and leave the market for high-class saloons to Rover and Jaguar. In fairness, it must be stated that the costs – both financial and in terms of lost performance – of making the PI engine compliant with ever-tighter Federal exhaust emissions standards would have been prohibitive, and it was most probably hoped that the forthcoming Stag would prove just as attractive to potential customers. The only 2.5PIs to reach North American shores would be a handful of private imports.
Despite its early success, the original 2.5PI would enjoy only a short lifetime in production. Even before it had been announced, work had commenced on the transition to a significantly revised Mk2 range and, with a full order book, there was little incentive for Triumph to undertake significant further development of the existing cars. Even so, a number of detail revisions were implemented, notably a series of fuel system modifications in order to address fuel pump starvation under hard cornering and, on some cars at least, potentially hazardous fuel leakage within the engine compartment. Furthermore, and so as to harmonise production of the two different types, the 2000 would adopt several of the features originally specified for the PI, the most significant being the uprated front brake assemblies, whilst the horizontal spare wheel stowage arrangement also seems to have been standardised on saloons at about this time. Lastly, from late 1968 both 2000 and 2.5PI models could be supplied to special order with brushed-nylon facings to the seats, though this option remained relatively rare.