User:Graham.Fountain/sandbox



The Triumph TR7 Sprint version of the Triumph TR7 sports car was produced in only very limited numbers by the Triumph Motor Company, then part of British Leyland, from about February to October 1977. There were probably a maximum of 61 cars in total; where only 3 cars are recorded as being made after early July 1977, all 3 for specific motorshows. Instead of the TR7 base model's 105 bhp DIN, 8-valve, 2-litre version of the Triumph slant-four engine, the TR7 Sprint used a 16-valve version of the Triumph slant-four, almost identicle with that fitted to the Triumph Dolomite Sprint, which gave 127 bhp DIN, but had originally been specified at 135 bhp SAE.

Why BL produced so few TR7 Sprints has been a matter of some debate. Of 30 cars built on the line at Speke over the end of June 1977, all but one have "UK PRESS VEHICLE" hand written in felt-tip pen on their build records. These cars are therefore assumed to have gone to the Press Garage at Canley when they left Speke in mid-July 1977; although, there does not seem to be any actual proof for that. Also, two cars went to the BL test track at Solihul, presumably as part of testing for UK type approval. Hence, it is widely assumed that the TR7 Sprints must have been built as part of a planned 16-valve TR7 production model, which was then cancelled after only these few had been made; though there are also no contemporary records for this. Whereas, author and Triumph TR enthusiast Bill Piggott argues that by 1977 "there was no need for it, especially as the TR8 was almost at production status", and notes that their disposal is unusual. However, changes to the FIAs rules for homologating cars for competion meant that BL needed at least 50 TR7s fitted with Dolomite Sprint 16-valve engines, and suitable for sale. This was to gain re-approval for the use of the 16-valve head on the Group 4 TR7 rally car, which would otherwise have been banned from the end of 1977 by these FIA rule changes. Also, the FIA required that rally cars must have type approval from April 1978. A second approval of the 16-valve head for the Group 4 TR7 was granted on 1 Feb. 1978; where similar approvals are known to have been given on production of 50 cars.

Technical specification
Engine:  Triumph Slant Four 1,998cc 16 valve

Capacity:  1998 cc

Valves:  16

Compression ratio:  9.5:1

Fuel system:  Twin 1¾" choke SU HS6 carburettors

Maximum Power:  127 bhp @ 5200 rpm (estimated)

Maximum Torque:  122 lb ft @ 4500 rpm (estimated)

Performance Data
0–60 mph:  8.5 seconds (estimated)

Max speed:  120 mph (estimated)

The improvements in the 0–60 time and top speed over the TR7's 9.6 seconds and 111 mph are not huge. However, the figures for the 16 valve version of the TR7 are almost identical to those for the US specification carburettor version of the 3.5 litre 135 bhp V8 TR8, which are 120 mph and 8.4 seconds. Also, one of the then Triumph engine development engineers is quoted as saying "The real test was the 30–50, 50–70 [mph] times and here the Sprint was significantly superior to the 2V [2 valves per cylinder] engine and even challenged the TR8's abilities. Certainly, if we were going 'off site' the preferred vehicle to 'borrow' was a Sprint TR7 over all others and that includes the TR8."

Also, The Sprint not only had more torque and power than the TR7, but peak values significantly higher in the rev range - presumably leading to a significant improved driver experience and the preference for this vehicle mentioned above. However, the production TR7 Sprints retained the gearbox and 3.9:1 final drive ratios of the TR7; where a number of converters of TR7s to TR7 Sprints suggests it benefits significantly from the use of the 6-cylender SD1's 3.45:1 final drive or, with tuned engines, even the SD1 3500 or TR8 3.09:1 ratio (which all fit the 5-speed TR7 axle). Hence, given a change in ratio, even to an available alternative value, the resulting figures might have been an even bigger improvement over the TR7's.

Further, despite being specified at 127 bhp, Spen King related "how he went away on holiday and came back to find an engine running on the bed giving 150 bhp at the first build." This would be very close to the 153 PS DIN (±5%) that was given by the Rover V8 engine in the UK Specification TR8 (and higher in the rev range). Hence, it is possible that had Triumph produced the TR7 Sprint and TR8 to UK specification, as was apparently planned at one time, there likely would have been significant debate of their relative merits.

Production details


According to the British Motor Industry Heritage Trust (BMIHT) archives at the British Motor Museum, Gaydon, there are production records for chassis numbers ACH/4 to ACH/25, and ACH/00501 to ACH/00535 and ACH/00700: 58 cars. Also, ACH 1 is identified by the TR Drivers Club, as UK registration WAC 274S, and that ACH 2 and ACH 3 existed might have been inferred from this: "One [unattributed] source states that there were three batches of Sprints, ACH 1 to ACH 25, ACH 501 to ACH 536 and ACH 700 on its own, a total of 62 vehicles." However, following a requested search of the BMIHT records it was discovered that "the build records we have for ACH/000535 cover 4 separate sheets and there is no record or build card for chassis number 536 as the next vehicle is chassis number 700."

While the 'A' in the ACH prefix to the commissioning numbers indicate that the factory TR7 Sprints were built at Speke, a Triumph engine development engineer is quoted as saying "Some if not all of these cars were definitely converted at Canley from 8-valve to 16-valve". The reason given for this is that "the Speke unions wanted added bonuses for dealing with 'non-standard' cars." However, at least some were built on the production line at Speke: another Triumph employee, responsible for engineering liaison between Speke and Canley, is quoted as saying that "At the changeover in July 1977 (to the new common underframe) we built a batch of thirty TR7 Sprints."

What production records there are at the BMIHT do not provide registration details from which cars might be traced; however, some further details of the cars known to have been produced are provided by the TR Drivers Club. The TR Drivers Club website gives details for only two of the first group of 25 chassis numbers: what was presumably the first prototype, WAC 274S, and one other, WAC 253S. Both known cars from this group were registered in Coventry in September 1977. It is suggested that most of the other cars in this batch were LHD and sold abroad. According to an inspection of the BMIHT archives, of the cars in this batch of 25 chassis numbers, at least were 11 LHD (some records have been lost) and 3 were UK specification - the remaining 11 are 'unknown' but assumed to be LHD.

The second batch of chassis numbers begin at ACH/00501. The addition of two leading zeros to this second group of chassis numbers to make them five digits, the same length as production TR7's chassis numbers, may indicate these were pre-production cars, not prototypes. However, the differences in where and by which division of BL they were registered (from their (V55) registration documents), indicates that they may still not have been manufactured as a single batch. Hence, it is possible that the press garage (SJW) cars were the "batch of thirty TR7 Sprints" built at "the changeover in July 1977", and the cars in the first group, and possibly some of the second, may have been those built as 8-valve cars at Speke, and converted to 16-valve at Canley.

The first two cars of the second group of chassis numbers were both white, and registered in Coventry as VVC 696S and VVC 697S in August 1977. These were, according to an owner written article in the TR Driver's Club Magazine from 1991, used for reliability testing. While there are no reliable details for BL's use of these actual cars, according to one source the procedure used with the TR7 and TR8 was to run a test car on the Belgian pavé track at MIRA for 1000 miles, "effectively providing wear harder than a vehicle might experience in a lifetime of normal use". The same source also states that "A related assessment exercise for the TR7 was the '90 day corrosion test', for which a prototype was built without the usual zinc primer or anti-corrosion treatments and the body painted white, the best colour to show up any rust streaks." A Triumph engineer is quoted as saying, "this prototype was run around a variety of road surfaces under wet conditions and then the damp areas were checked. The vehicle was then fitted with a series of nozzles which sprayed salt solution into these same areas".

Thirty cars from this second group of chassis numbers were sequentially registered SJW 521S to SJW 550S (see Figure 4) in Birmingham in three groups in November 1977. Most of these cars have"UK PRESS VEHICLE" handwritten in felt-tip pen on their build cards, and it has been claimed that these cars went to the BL press garage at the Canley site, Coventry; presumably for publicity purposes. There are transport stamps on their build records showing they left Speke in mid-July 1977. However, there is no indication to where they were transported, only that they were in the keeping of the Sales and Marketing Dept., Longbridge, when they were registered and transferred to Power Train and Foundry Division, indicated as the "selling dealer" in November 1977. It is also claimed that these cars were stripped and re-trimmed, and possibly also re-sprayed, as would have normally been the case with press cars; and that they would have had their turret tops smoothed over in that case. However, the TR7 Sprint Homologation pictures show no evidence of this work, even though the pictures were taken only days before that car's disposal by Sales and Marketing Dept., and months after its production and departure from Speke in July 1977. Many of these SJW cars do state on their build record search certificates from the BMIHT that they were for a press release. However, according the BMIHT archive staff, that note is only due to the "UK PRESS VEHICLE" notes on their build cards.

Another car of this second group of chassis numbers was registered in Coventry as ARW 181S in July 1978. According to a letter from the then archivist, reporting the research of the BMIHT records, "This car was originally intended for display at the 1977 [ Daily Express ] Motorfair in Earls Court, London. We can not verify whether it was in fact displayed here." This car was factory fitted with engine CH 2 HE which it still has as of September 2017. It seems that the last car built in October 1977, ACH/00700, was also intended for a motorshow in Scotland. However, again, it is not known if it was actually used for that.

Distinguishing features
"There are a [comparatively] large number of privately built Sprint conversions about... Buyers should beware of this if they are asked a premium price for an alleged 'genuine' TR7 Sprint": all the essential parts to turn a TR7 into a functional copy of a TR7 Sprint, though not an identical one, can either be sourced from a Dolomite Sprint or remain available from suppliers; several companies sell conversion kits online; and several sources provide information and advice on this TR7 Sprint conversion. One of which states, "this upgrade brings you into the same power band as an original TR8, but for a fraction of the cost, effort and time." There are also a number of websites dedicated to the Sprint and Sprint conversions, and at least one forum.

It seems that there is no disagreement that "[a]ll [factory TR7 Sprint] cars were fixed-head coupes", that the period over which they were built spans the changeover between the 1977 and 1978 year models, and both right and left hand drive cars were produced. Those TR7 Sprints that are known were fitted with the 5-speed gearbox mated to the 3.89:1 rear axle that was standard on the 5-speed TR7s. The pre-production cars had the alloy wheels that were optional for later TR7s and standard on Solihull built fixed-heads.

Engine and interior
The factory produced TR7 Sprints have chassis numbers that are prefixed with letters ACH; whereas, UK/Australian/European specification TR7s of the time were prefixed ACG: Figure 5 shows a chassis or commissioning plate from a TR7 Sprint car, mounted on the left-hand door, below the door lock. The TR7 Sprint engines are also prefixed with CH, rather than GC on the TR7's and VA on Dolomite Sprint engines; however, the TR7 Sprint engine numbers can, at least in some cases, be very hard to read (see Figure 6).

There are a number of auxiliary engine parts specific to the TR7 Sprint, and not used on the Dolomite Sprint engine: the cast steel exhaust manifold (RKC2788), the front pipe of the exhaust system (which has been remanufactured, RB7385), and a water transfer plate at the back of the cylinder head (also remanufactured, RB7240).

A number of parts in the throttle linkage are also unique to the TR7 Sprint, most obviously the (unused) air-conditioning full-throttle cut-off switch mounting plate between the two carburettors (just visible in Figure 2, and partially obscuring the inlet manifold in Figure 3), which was not fitted to the Dolomite Sprint; and the throttle lever/link rod (visible just over the air box in Figure 3), which looks the same as the TR7 part, but is longer to allow for the carbs being further apart.

The front disks were specific to the TR7 Sprint, although the callipers and dust shields, etc., were as those used on the TR8; so TR8 disks fit.

There are also at least two different Engine information panels (UKC 8605 and TKC 5228), on the underside of the bonnet, some of which only indicate TR7, but provide slightly different information to that on the equivalent TR7 part (UKC 6246).

There are online photographs of some of these parts.

At least some of the cars were fitted with the large semi-circular pad on the steering wheel from the US specification TR7 (RKC82) (see Figure 7).

There is one unsupported claim that "Having a higher-revving engine, the Sprint received a recalibrated rev counter". However, this is incorrect: both engines had a rev limit of 6500 rpm indicated on the rev counter, though both owners' manuals give the "Maximum recommended engine speed (intermittent)" as 6,000 rpm. Hence, the TR7 and TR7 Sprint shared a common rev counter.

Exterior


It appears that the exterior of the pre-production TR7 Sprints was, and presumably the production cars would have been, indistinguishable from the TR7 of the day, apart from the decals and side stripes. However, it is reported that a number of different decal sets were being tried out on the prototype cars.

There are a number of published photographs of TR7 Sprints bearing decals simply comprising the word "SPRINT" on the front panel and boot lid below the 'TR7' decal of Speke built TR7s,  and described as "The logo that appeared on the boot lid of most of the few TR7 Sprints that escaped from the factory." These used the same font as the TR7 decal applied to Speke built TR7s and in the side stripes used later on the TR7 Premium edition. There is also a description of a car "with the word 'Sprint' written large on the right of the boot lid, the TR7 decal being on the left". However, none of these photographs can be identified to cars that had not been owner modified. Whereas, these decals form part of the set displayed on the FHC TR8 shown in the TR8's homologation papers (FIA #654), identifying it as a "Sprint TR7 V8". These Sprint decals were at one time available (in three sizes) from Moss Europe (previously TriumphTune), though they were not catalogue items or identified to a BL part number or numbers. One size is still available as supplier part No. RB7206BLACK/SILVER/GOLD.

There is also a published photograph of what appears to be a US Spec., pre-1978 year model car carrying side stripes with the word "Sprint" on the rear wings, the caption to which states "The sides of the TR7 Sprint were supposed to have received this striping treatment, designed by John Ashford, had the car gone into production." These stripes were later reworked for the TR7 Premium edition after the TR7 Sprint was still born. These side stripes were, at one time, listed by Moss Europe under BL part numbers YKC2082-2087. They are also shown in a series of 6 "TR7 Sprint Homologation" photographs in the BMIHT Film and Picture Library, taken on 1 November 1977 before the car was sold-off by BL. The car in these photographs from the BMIHT does not carry the "SPRINT" decals, described above, on either boot lid or front panel. The TR7 Sprint shown in figures 1 and 8 is, in this respect, identical with these photographs, except for the colours.

Publications
The BL TR7 Repair Operations Manual, AKM3079A, covers both the 4 and 2 valve (per cylinder) engines; however, an erratum stuck to the title page states "At the time of going to press the 4 valve engine referred to in this manual has not been fitted to the Triumph TR7".

An owner's handbook, AKM 3967, was also produced for TR7 Sprint in 1977, but is apparently for the 1977 year model: it shows the interior light in the headlining not the doors. Also some of the information is incorrect for the TR7 Sprint, i.e. pictures show the 8 valve engine and the TR7's AC Delco distributor. However, it also lists only the 5 speed (LT77) gearbox, unlike the similar handbook for the TR7, RTC 9210, which lists the 4 speed, and the 5 speed as an option.

The FIA's 1976 rules for homologation, which applied to the re-homologation of the 16-valve head for the group 4 TR7 rally car, approved in February 1978, state that in "checking of a model of car against its recognition form" the scrutineers may refer to "the maintenance booklet published for the use of the make's distributors". These two documents may have been intended to fulfil such a requirement, since the handbook is not intended for the distributor and the ROM is not well described as a booklet.

Motorsports
The TR7s used by BL in Group 4 rallying, from their advent in the Welsh rally of 1976 to the Circuit of Ireland in 1978, also used (tuned) 16-valve 2 litre Sprint engines, which by 1977 was rated at "rated at 225 bhp at 8000 rpm". These 16-valve TR7 rally cars proved competitive on asphalt, winning a number of events including the Belgian Boucles de Spa rally in 1977. They were replaced by the Rover V8 3.5 litre engined TR7V8.

Four of the later BL works rally cars carried the registrations of cars from the press garage, SJW 533S, SJW 540S, SJW 546S, and SJW 548S. SJW 533S was initially campaigned as a 4 cylinder 16 valve car, and later as a V8 3.5 Litre TR7V8 specification. The other three were only ever campaigned as TR8s. However, it is not clear whether or not the four rally cars bearing these registrations actually were, in any real sense, the TR7 Sprints from the press garage, or whether only the registrations were used. There is a story at one TR7 related website, and already current in the 1980s, that John Davenport, "needed white cars without sunrooves [sic] and these were the nearest four." However, Bill Price wrote "As I think is known, four of the [TR7] Sprint press release car registration numbers were 'inherited' by BL Motorsport and used to identify four TR7 V8 'works' rally cars." Also, according to the press garage data (Figure 4), SJW 533S was russet, SJW 540S was java green, SJW 546S was brooklands green, and SJW 548S was carmine; though none had sun-roofs. While there are suggestions that the cars sent to the press garage were re-trimmed and even possibly re-sprayed, there are no suggestions that their paint colours were changed, and the competitions department could, presumably, have managed that themselves, were it significant. Equally anecdotally, a more complete reproduction of the 1991 owner written article from the TR Driver's Club magazine states "Although the SJW TR7V8 rally cars began life as TR7 Sprints, the rally cars were scratch built using bodies taken off the line and prepared by Safety Devices. So only the registration numbers from the sprints were used."

Initial homologation
There is some confusion over exactly how the TR7 was homologated (for group 4) with the 16 valve engine, close ratio sprint gearbox and overdrive, and heavy duty rear axle before any TR7 Sprints were produced. Rally journalist and historian Graham Robson refers to the "famous 'inventive homologation' skills" of Bill Price, then workshop manager at BL Special Tuning (ST) at Abingdon, and to him "perhaps, taking lessons from Ralph Broad, who was an old hand at the black art of 'reading the rules'", and states that "Bill [Price] managed to gain approval for a TR7 which was only loosely related to the production car." Bill Price himself wrote on this issue "Careful consideration was given to the existing specification with the result that we decided to list the 16-valve Sprint cylinder head to enable us to virtually transplant the Sprint rally engine into the car. The Sprint gearbox was homologated as the 77mm five-speed [LT77] gearbox was not yet available and it would take time to produce close ratio gears for it. The heavy duty axle which would be standard with the five-speed gearbox was also listed [for Group 3] as an [export] option". However, Graham Robson quotes BL Motorsport director John Davenport remembering "that the '100-off' rule applied to alternative engines at the time (which explains why Ford was able to race 24-valve four-cam Capris in 1974), but this waiver never applied to transmissions."

The 100-off rule, to which John Davenport referred, was a section of the FIA's rules for homologating Group 4 cars (actually, for homologating Group 2 cars, but also applicable to Group 4). It covered a list of "Optional equipment which may be recognized with a minimum production of 100 units per year to equip 100 cars". While John Davenport was correct that, in 1975, this list included alternative cylinder heads with different numbers of valves, it also did include alternative gearboxes with overdrives, flywheels, clutches and their housing, and many other engine, transmission, and suspension components. Such optional equipment could be recognized as "bolt-on option kits", which had to be "available freely at the manufacturer's or his dealers' for any one wishing to purchase it" - as would have been the case with the 16-valve head and its drive (pistons, carbs, and manifolds could be changed freely for Group 4), and for the overdriven gearbox, which would have been available as spare parts for the Dolomite Sprint (the heavy duty axle was homologated for Group 3, and thus 4, by a different means). But when the 16-valve TR7 was homologated for Group 4 in October 1975, the 100-off rule did not require the production of any 16-valve engined TR7 road cars, only the kits needed to equip them.

A number of other modifications were listed in the amendment (1/1V) to the TR7's homologation for the Group 4 TR7, such as larger front callipers and rear disk brakes. These were allowed from a list of "Optional equipment which may be recognized without a minimum production". Other modifications that are not listed in the papers, such as suspension components and axle locating arms, etc., were given as freely allowed to be changed or added without need of being specifically recognized as part of the homologation process.

FIA Rule change for 1976
In the rules applying for 1976, published soon after the TR7 was homologated for Group 4 in December 1975, and "[e]ffective from the end of 1977, the FIA banned alternative cylinder heads", and many other parts homologated in 1975; in effect, they revoked their 1975 approvals from the end of 1977. As a result, those cars fitted with alternative heads, etc., either had to return to the components of the cars used to homologate the model, or have the parts re-homologated under the new rules; and without the 100-off rule that meant producing cars fitted with them. Several teams are reported to have removed such multivalve heads from their cars, including the Toyota Celica, Vauxhall Chevette HS, and Lancia Stratos. Ford, however, produced additional Ford Escort RS1800 (X0) cars in 1977 and were able to continue to use it (transferred to Group 4 as the Escort RS) with the BDG engine (a 16-valve Cosworth head on an aluminium alloy version of the Kent block) in 1978.

This ban would come into effect before the TR8 - which was intended to replace the TR7 in rallying -, would be ready: "John Davenport's team had not been certain it would be available to them until the very day that homologation was granted - on 1 April 1978." Hence, BL had the Sprint 16-valve head recognized for use on the Group 4 TR7 a second time, which was granted in February 1978 in time for its use in the Mintex rally of that year. This required the production of at least some 16-valve engined TR7s "meant for normal sale", i.e. "distribution of cars to individual purchasers through the normal commercial channels of the manufacturer". While the rules did not specify that any of these cars actually had to have been sold for approval to be granted, it is noted that "[f]ollowing the cancellation of the project, normal practice might have been to dismantle the cars or convert them to normal TR7 power, but surprisingly most were sold off to private buyers." This is supported by what happened to the 25 or so cars of the failed O-series engine TR7 development programme, which were either scrapped or converted to TR8s before sale.

While the number of cars required by the FIA to homologate a modification to a Group 4 car does not appear to given, the production of 50 or so cars is known to have been sufficient for some similar modifications of the era, such as the 1977 RS1800 X0 version, the Vauxhall Chevette HSR, and the Porsche 924 Carrera GTS. The role of the TR7 Sprints in this process is shown by the series of 6 photographs of one of the press garage cars (later registered as SJW 530S), taken on 1 November 1977, listed in the BMIHT Film and Picture Library as "TR7 Sprint Homologation".

It may also be noted that production of the TR7 Sprints began almost immediately after the homologation of the 5-speed TR7 for group 3 (in January 1977), when the specification of the 16-valve cars needed to re-homologate the head would have become clear, and that production basically stopped soon after 50 cars had been produced around the end of June 1977 (only 3 cars produced after that, probably all for specific purposes). It may also be noted that in mid-November 1977 (9th to 23rd), just after the homologation pictures had been taken, the 30 SJW cars, supposed to have gone to the press garage, were transferred out of the keeping Sales and Marketing Longbridge, into that of the Power Train and Foundry Division (listed as the "Selling Dealer"), which is identified in the process of the disposal of similar cars.

Cancellation
There had been significant speculation regarding the possible production of a 16-valve version of the TR7 from the outset. This was because the two engines used the same block, etc., so it seemed an obvious development. It is even claimed that the 16-valve version of the TR7 was one of the most anticipated sports cars of the 1970s. As these cars were clearly built to be sold, and at least most were, it has been widely assumed that the TR7 Sprints were built as the start of full series production that was cancelled after only these few cars had been made.

The usually suggested reason for this unusually timed cancellation is the 17-week-long strike at the BL Speke plant, where the TR7 and at least some of the TR7 Sprints were manufactured, which started on 1 November 1977. This resulted in the closure of the Speke plant in May 1978 and the move of production to Canley, Coventry. This caused major losses to production and so a significant loss of BL's market share. These issues, it is claimed, then led to the cancellation of the TR7 Sprint, and is why the production of the 16-valve TR7 Sprint module did not restart at Canley after the move. However, these events all occur well after the main production of the TR7 Sprints ceased in early July 1977 (only 3 more were made after that, all for specific motor shows), and too late to be responsible for the change of status indicated by the export of the LHD cars on 2 Nov. 1977, and the 9 November 1977 start of the transfer of the press garage cars out of the keeping of Sales and Marketing to Power Train and Foundry Division as the "Selling Dealer". Neither do they address the question implied by Bill Piggott in stating "it could be argued that there was no need for it, especially as the TR8 was almost at production status in 1977 when the Sprints were manufactured." Nor yet is it explained why "surprisingly most were sold off to private buyers" when "[f]ollowing the cancellation of the project, normal practice might have been to dismantle the cars or convert them to normal TR7 power" - as happened to the 25 or so O-series engined TR7 version development cars when that programme was cancelled a few years later. It was also noted in 2009 "One might imagine that for a vehicle built less than 35 years ago definitive records would still be available, but... this is not so." Another possible reason given for the cancellation is that "the Marketing department killed it because the 0-60 acceleration times were identical to the 2V engine with little increase in top speed". However, this lack of significant difference is also disputed, and no reason is given for why any TR7 Sprints should have been produced if Sales and Marketing did not want it.

Whereas, author and journalist David Knowles explains the cancellation with a quote from Mike Dale, then BL US VP of Sales and Marketing, stating that "The next shoe to fall was the four valve. It died and wiped out a model option for us." Knowles identifies this "four valve" as the electronic fuel injected (EFI), cost-reduced, slant-four engine from the Triumph SD2 programme, which was intended to be compliant with upcoming (1976) US emissions requirements: this parallels the use of the V8 engine from the much larger production Rover SD1 in the TR8, the relatively small production uprated version of the TR7 that actually was produced for the US. Triumph car enthusiast and author Bill Piggott also states "at the time the [TR7] Sprint was aborted, a fuel injected version of the 16-valve engine was under development for it". There does not appear to be any evidence that this 16-valve EFI engine was intended to be used with the Dolomite Sprint, and no Dolomites are known to have been fitted with it - though it seems there was a black TR7 fitted with this engine and used by BL for development in the early 1970s. Also, a prototype SD2 in the BMM at Gaydon is fitted with an EFI engine that appears identical with the Dolomite Sprint engine, other than the EFI system, ancillaries, additional connections for a smog pump, and manifolds. Note: the exhaust manifold used in this SD2 bears the same cast-in part number (with a separate letter "A") as that used on the TR7 Sprint, and appears to have the same fitting to the exhaust pipe. It also appears to have the same casting for the cabin heater at the back of the head, though the part number is not visible.

It is also widely noted that the SD2 programme was cancelled in 1975 as a result of the 1975 Ryder report. That report followed the effective bankruptcy of BLMC in December 1974, and provided the nearly £3 billion rescue plan for BL through ownership by the National Enterprise Board, and identified BL’s critical need for rationalization of the range of competing models and engine types produced by BLMC. It also appears that the 16-valve TR7 was to be aimed very much at the US market, like the TR7 itself and, even more so, the TR8 uprated version of the TR7 that did go into production for that market. It would therefore have been produced in such small numbers that it needed a US emissions compatible engine from a car of much larger production numbers, just as the TR8 used the Rover V8 engine from the Rover SD1, which not even the Ryder plan was able to stop. In which case, the US emissions compatible engine would have been cancelled with SD2, and that would mean the 16-valve TR7 model was cancelled in 1975, well before the TR7 Sprints were built.

However, even with the catalogued 16-valve TR7 production model cancelled, the TR7 Sprint still needed to be built for the re-homologation of the 16-valve head for use on the Group 4 TR7 rally car, as is described above. Their being built solely for that reason then explains why they were built when "the TR8 was almost at production status", and the reported lack of documentation for the production of the model in 1977. It also explains why they were sold to private buyers rather than dismantled or returned to normal TR7 power, the timing of the start of that production in Feb. 1977 with the Group-3 homologation of the 5-speed gearbox and heavy-duty back axle, and the timing of the end of main production in July 1977 when just over 50 properly documented cars needed for the homologation and the model type approval had been built. The FIA requirement for supporting documentation for the model to be made available to scrutineering also explains the publication of the owners handbook and a version of the TR7 repair operations manual covering the 16-valve engine.