Grandfather’s Ax: The Many Evolutions of the Triumph TR4, Part 2: TR5, TR250, and TR6

With the debut of the TR4A in 1965, Triumph finally had a sports car with a modern fully independent suspension to match its crisp Italian styling, but the company soon decided the TR needed more power and a fresh suit of clothes. The results were two familiar-looking cars with completely new engines, followed less than two years later by a fresh-looking model whose specifications were pure déjà vu. In the second part of our history of the TR4, we look at the 1968-1976 Triumph TR5 PI, TR250, and TR6.

1968 Triumph TR250 badge


In our first installment, we chronicled the origins and development of the Triumph TR4, launched in the fall of 1961 to replace the previous TR3. An amalgam of several different styling studies by Turinese designer Giovanni Michelotti, the TR4 was essentially a new body on a warmed-over TR3A chassis, distinguished mechanically by a wider track, rack-and-pinion steering, and the standardization of the previously optional 2,138 cc (130 cu. in.) “wet-sleeve” OHV four.

The TR4’s new styling and greater civility were well-received, but many a critical spleen was vented at the harsh ride and unsettled rough-road handling. In response, Standard-Triumph developed a new chassis with fully independent suspension and mated it to a little-changed body to create the TR4A, introduced in March 1965.

1966 Triumph TR4A front 3q © 2009 AlfvanBeem PD AS mod
A Dutch Triumph TR4A convertible; next to it is a TR4A hardtop with the center roof section removed. Assuming both were originally European cars, both have independent rear suspension, which was optional on North American TR4As. The chrome rub strips across the front fenders and doors were new to the TR4A and one of the easiest ways to distinguish this model from the early TR4. (Photo: “Triumph TR4A dutch licence registration AL-47-75 pic1” © 2009 AlfvanBeem; dedicated to the public domain by the photographer under a Creative Commons CC0 1.0 Universal Public Domain Dedication, resized and modified (retouched, obscured numberplate, and removed some bystanders in the background) 2012 by Aaron Severson)

The updated chassis gave the TR4A a much better ride if not necessarily better handling, at least on smooth roads, but underscored the fact that the TR could use more power. By the factory’s reckoning, the TR4A was 190 lb (86 kg) heavier than the TR3A, while engine output had increased by only 9 gross horsepower (7 kW) and 15 lb-ft (20 N-m) of torque. The TR4A was still one of the quicker cars available in its price range (around $3,000 in the U.S., £800 plus tax in the U.K.), but the giant-killing days of Triumph’s earlier TR2 and TR3 were a fading memory.

Deciding the best way to get the TR4 the additional power it needed was the subject of much internal discussion. It was certainly possible to coax more horsepower out of the existing engine — in racing tune, the 2,138 cc (130 cu. in.) four was good for a reliable 150+ horsepower (112 kW) — but doing so sacrificed much of its robust low-end torque and admirable fuel economy. Expanding the bore to bring displacement to a full 2,499 cc (152 cu. in.) was also a possibility, but meant redesigning the block and did nothing for refinement, an area in which the venerable three-bearing four had never particularly distinguished itself. There were also the forthcoming U.S. federal emissions standards to consider, problematic for a 20-year-old engine design. Standard-Triumph eventually decided that the wet-sleeve engine had had its day; the big four was now used only by the TR4 and a handful of Morgan Plus 4s, so sinking more money into its development was a questionable investment.

1969 Triumph 2.5 PI engine © 2012 Akela NDE CC BY-SA 2.0 France
Triumph’s new fuel-injected 2.5 PI six-cylinder engine, seen here not in a Triumph TR5, but in a Mk 1 2.5 PI saloon. For saloon duty, the 2,498 cc (152 cu. in.) six received a milder cam, restricting output to 132 net horsepower (98 kW) and 153 lb-ft of torque (207 N-m), but improving low-end response: Torque peaked at only 2,000 rpm compared to 3,500 rpm for the more powerful TR5 PI engine. (Photo: “Triumph 2.5 PI Mk1 interior in Morges 2012” © 2012 Akela NDE; resized 2012 by Aaron Severson and used under a Creative Commons Attribution-ShareAlike 2.0 France license)

From the standpoint of production economy, the better choice was to adopt the newer straight six from the Triumph Vitesse/Sports 6 and 2000 saloons. However, that was no solution to the TR4’s power deficit: As used in the big saloon, the 1,998 cc (122 cu. in.) six gave away 14 hp (10 kW) and 15 lb-ft (20 N-m) of torque to the elderly wet-sleeve four. Tinkering with the carburetion and cam profile improved power but not low-end torque, so Standard decided to redesign the six’s block to allow a hefty 19mm (0.75-inch) stroke increase. The result was a new 2,498 cc (152 cu. in.) engine that could be used both in a six-cylinder TR (codenamed Wasp) and future editions of the big saloon.

For the Wasp, Standard-Triumph raised the six’s compression ratio to 9.5:1, added a much hotter camshaft, and traded the saloon’s Zenith-Stromberg 150CD carburetors for Lucas Mk 2 mechanical fuel injection. Fuel injection was still racy stuff in the mid-sixties and Triumph would be the first British automaker to adopt it for a regular-production petrol engine; even most exotics still used Weber carburetors. Designed by the Lucas Injection Lab, the Mk 2 system was an adaptation of the Mk 1 setup used by some race cars, using a similar constant-pressure fuel pump and distributor-driven metering rotor, but unlike the racing system, fuel flow was controlled by six vacuum-operated butterflies rather than a mechanical throttle linkage. Because fuel metering depended on engine vacuum, its precision at off-idle speeds was less than ideal, but testing in 2000 saloons from the works rally team revealed that the injection system’s long intake runners and improved fuel distribution provided much better drivability with the wilder cam profile than carburetion. The result was a satisfying 142 net horsepower (106 kW) and 164 lb-ft (222 N-m) of torque from an engine very little larger and actually a bit lighter than the old four.

1968 Triumph TR250 bonnet
While the bonnet of the six-cylinder Triumph TR5 PI/TR250 looks the same as that of later TR4s, it is actually yet another variation with different bracing and latches than either of the two previous “long-bulge” versions. The protuberance was unnecessary with the six-cylinder engine, which sits slightly lower than had the four and had no carburetor clearance issues; we don’t know why Standard-Triumph didn’t simply eliminate the bulge. Wire wheels were optional on six-cylinder cars and much better looking than the standard wheel covers. (author photo)

The Wasp’s other changes were few. Larger front discs were added to cope with the additional power and an alternator replaced the previous generator, presumably to better accommodate the demands of the constant-pressure fuel pump. The previously optional brake servo and 165HR-15 tires were standardized, the rear springs were stiffened in an effort to reduce acceleration squat, and the rear axle ratio was reduced from 3.70 to 3.45 in hopes of preserving some semblance of fuel economy. In the cabin, the switchgear was revised to comply with U.S. safety regulations, but the only noticeable cosmetic changes were a slightly revised grille, “2500” badges on the rear fenders, and some rather tacky styled wheelcovers.


Standard-Triumph engineers had high hopes that the fuel-injected six would be an expeditious way to increase refinement, improve power, and meet U.S. emissions requirements all at the same time. Alas, the sticking point once again was cost. Since Triumph’s U.S. distributors had already balked at the price of independent rear suspension, it isn’t difficult to imagine their feelings about fuel injection, which would have added at least $400 to the TR’s list price. Moreover, the injected “2.5 PI” engine ran rich, particularly at low speeds, and Triumph soon discovered that getting the six to pass federal emissions standards would require the addition of an air injection pump, adding to the engine’s already substantial production cost.

1968 Triumph TR250 dash
The TR5 PI and Triumph TR250 had the same dashboard with the same basic layout as the TR4A dash, but with matte-finish wood veneer and new switchgear to comply with U.S. safety standards that took effect January 1, 1968. This dash was retained on the TR6. (author photo)

By contrast, simply lowering the compression ratio to 8.5:1, reverting to two somewhat modified Zenith-Stromberg 175CD carburetors, and making some minor engine changes (such as limiting maximum intake vacuum) would allow the 2,498 cc (152 cu. in.) six to pass muster without add-on hardware, reducing manufacturing costs significantly. The consequence was that the carbureted six was only fractionally more powerful than the big four, making 111 gross horsepower to the four’s 109 (83 kW vs. 81); net ratings were identical at 104 hp (78 kW) for both engines. However, the six still had considerably more torque — gross figures were 152 lb-ft (206 N-m) for the six, 132 lb-ft (179 N-m) for the four — and was much smoother and quieter than the old wet-sleeve four. The carbureted six also promised fewer service headaches than the fuel-injected engine — no doubt a reassuring point for the North American organization, which had been uneasy (rightly, as it turned out) about the warranty implications of the costly and unfamiliar Lucas injection system.

North American cars received a few other changes, many of them at the insistence of J. Bruce McWilliams, the former Rover executive who had become executive vice president of marketing for Leyland’s U.S. organization following the merger with Rover in late 1966. Most of the modifications were cosmetic: brighter colors and a contrasting paint stripe across the nose, tricks McWilliams had developed at Rover as an inexpensive way to pep up sales. North American cars retained the unfortunate mag-style wheelcovers, but more functional changes included the use of wider radial tires (185SR-15 Goodyears in place of the European car’s 165HR-15 Michelins) and the TR4’s shorter 3.70 axle ratio. There was also a new name. While the injected car would be badged TR5 PI (for “petrol injection”), the carbureted edition would be called TR250.

1968 Triumph TR250 side
The stripe across the bonnet and front fenders marks this as a TR250, which traded Lucas injection for two emissions-controlled Zenith-Stromberg 175CDSE carburetors, their mixture controls sealed to prevent tampering. Gross output was 111 hp (83 kW) and 152 lb-ft (206 N-m) of torque, 104 hp (78 kW) and 143 lb-ft (194 N-m) net. The live-axle/leaf-spring suspension standard on North American TR4As was no longer offered, so all TR250s had fully independent suspension. (author photo)


The Triumph TR250 went into production in August 1967 with the TR5 PI following about two months later. Even with the cheaper carbureted engine, the TR250 was significantly more expensive than the TR4A, in part because the independent rear suspension was now standard: base price was $3,395 POE New York, over $300 more than a TR4A IRS. In the U.K., the TR5 PI’s basic price was at launch was a hefty £925 (£1,212 5s 5d with purchase tax), £125 more than a TR4A. By the spring of 1968, the injected TR5 was up to £985 (£1,260 13s 11d with tax), over £100 more than a six-cylinder MGC.

1968 Triumph TR5 PI front 3q © 2009 AlfvanBeem PD AS mod
The Triumph TR5 PI looks almost identical to the TR4A, but the grille is different and there is no longer a hole for the external starter handle optional on the TR4 (although the notch for it below the grille remains). Under the bonnet, the radiator is mounted farther forward than on the four-cylinder cars to allow clearance for the longer six-cylinder engine. The TR5 PI is actually a bit lighter than a TR4A with independent rear suspension, but is slightly more nose-heavy. (Photo: “Triumph TR 5-PI 96-27-FR” © 2009 AlfvanBeem; dedicated to the public domain by the photographer under a Creative Commons CC0 1.0 Universal Public Domain Dedication, resized and modified (recropped, obscured numberplate) 2012 by Aaron Severson)

The American press was less than ecstatic about the TR250, having been presented for the third time in seven years with a new and more expensive TR that was no faster than its predecessor. A few period reviews indicated that the TR250 was actually slower, although the disparity was probably attributable to the fact that the TR4’s optional 4.10 axle ratio was no longer offered except by special order. Either way, performance was not sufficient to keep reviewers from grousing about the overly familiar styling, dated body structure, and a suspension that still didn’t seem quite sorted. Owners soon complained about the emissions-controlled carburetors, which were temperamental and could not be adjusted.

The TR5 PI met a better reception abroad. If there were still doubts about the chassis, they were mostly compensated by the strong new engine. The injected six was much thirstier than the old four, demanded super-premium (100-101 RON) fuel, and had a rather rough idle, but endowed the TR5 with muscular performance. Despite a taller axle ratio, 0-60 mph (0-97 km/h) was now achievable in around 8 seconds and top speed with overdrive was close to 120 mph (193 km/h). That wasn’t fast enough to threaten an E-type Jaguar, but would administer a sound thrashing to almost any new car in the TR’s price range. The rival MGC, marginally more powerful on paper, was no match at all for the Triumph.

1968 Triumph TR5 PI rear 3q © 2009 Robotriot CC BY-SA 3.0 Unported
From the rear, the main distinguishing features of the Triumph TR5 PI are the exhausts (still duals, but with both outlets on the left rather one than on either side of the car), the “2500” badges on the rear fenders, and the backup lights (reversing lamps) beneath the taillights. This car’s luggage rack is not stock, nor are the wire wheels, a £38 6s 8d option on British cars. (Photo: “Triumph TR5 PI Heck” © 2009 Robotriot; resized 2012, 2014 by Aaron Severson and used under a Creative Commons Attribution-ShareAlike 3.0 Unported license)

From a reliability standpoint, however, American buyers may have been better off with the carbureted engine, as the injection system proved quite troublesome. In principle, it was not an overly complicated device (although even the Lucas development engineers thought the use of six separate butterflies was a mistake), but it required a level of manufacturing precision that was hard to achieve on an automotive assembly line or in a dealer service bay. A case in point was the metering diaphragm, whose springs had to be carefully matched to each unit and could not be adjusted; the service manual was full of stern injunctions not to tamper with them. The injectors themselves were designed for easy replacement, but the metering unit required an expert touch and Triumph preferred to replace the unit rather than attempt to repair or rebuild it. Owners were well advised to regularly change the fuel filter, which Triumph recommended every 12,000 miles (19,000 km), and to not let the fuel level drop too low, lest hard turns expose the pump pickup and allow air into the system. The pump seals could also give trouble.

The TR250 sold reasonably briskly in the U.S. — 8,484 units during its short run — but was well off the pace of the four-cylinder TR4. The six-cylinder car also commanded less loyalty than its predecessor; in a 1969 Road & Track owner survey, over 40% of TR250 owners said they wouldn’t buy another. The U.S. competitions department had no great luck with the TR250 either. The SCCA had reclassified the six-cylinder car in C Production, where it was simply outgunned.

The TR5 PI accounted for only 2,947 units, a sign of how important North America was to Triumph’s overall sales volume. Fewer than 1,200 TR5s went to the U.K., but that was actually considerably more than the yearly average for the TR4, which had always been rather scarce in the home market. The 2.5 PI engine found greater success in a different platform: In late 1968, Standard-Triumph installed a more mildly tuned version of the injected six in the 2000 saloon to create the sporty 2.5 PI, which outsold the TR5 by more than three to one.


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  1. Thanks very much for your well-researched article. It brought back many happy memories of my all too brief years with my restored 1967 TR4A IRS. I’ve often fantasized about tracking down and importing a TR5, but your description of the overly fussy PI has driven the last nail in that coffin.

    1. A lot of mechanical injection systems are fairly fussy things, at least in street car applications. The big problem, from an ownership standpoint, is having someone who knows how to work on it when necessary. That can be a big headache with a system not ever sold in the U.S.

      1. Peugeot offered Kugelfischer mechanical injection on the 404 and 504 in some markets, but the United States wasn’t among those markets. The KF6 injected engine was based on an entirely different block from the XN1 carbureted engine. The BMW 2002tii also used Kugelfischer injection. I don’t have any hard data on these systems, but I think it would be out of character for Peugeot and BMW to adopt a troublesome system. And then there was the Spica injection system, which Alfa-Romeo used for some years.

        AFAIK an outfit called Ingram Enterprises in Washington state is the only company in the US that offers parts and service for Kugelfischer and Spica injection. If I were thinking of getting a Kugelfischer- or Spica-equipped car, I’d want to satisfy myself that they have a succession plan for when the owner dies or retires.

  2. Did I miss mention of the TR6 PI listed in the title link?

    1. It is described in the text (it’s not in the title, but the title was already getting long). However, the TR6 PI was in most mechanical respects a TR5 PI with the restyled body. There were some mechanical changes to rationalize production with the 2.5 PI and to back off on the cam timing for a smoother idle, at the cost of some power.

  3. Why wasn’t the TR250 badged TR5 in North America?

    1. I never found an authoritative answer. My guess is that the TR250 name was something the U.S. importer came up with to try to highlight the presence of the new engine, since the six-cylinder car looked basically the same as the TR4/TR4A. Presumably Standard-Triumph was less worried about that in the UK, where the novelty of the PI engine was the main draw.

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