Triumph Press Information
DEVELOPMENT OF THE SPRINT ST
The Sprint STs design project team saw from the outset that the ST would have to be a completely new bike, purpose-built in order to satisfy the exacting demands of the design brief. Even so, the Daytona 955i clearly provided a very sound platform on which to base the new machine, so it was used as a starting point to begin the Sprint STs development.
Initially it was planned to use the 885cc engine from the T509 Speed Triple to power the Sprint ST, but in anticipation of advances by the competition it was soon decided to take advantage of the 955cc engine from the 955i for the extra torque which could be achieved, a crucial element in a sports tourers repertoire. The engine would be retuned to enhance its torque at low to medium revs, yet still produce a targeted, market-leading, maximum power of 112PS.
In addition, the Sprint ST needed to be particularly sophisticated and non-intimidating, so a great deal of work went into the engine management system, where exceptionally good transfer between the points on the fuel-injection mapping was achieved. The result is an extremely smooth and easy-to-use engine. This is exactly what the design team was aiming for, but even they were astonished at the amazing fuel consumption figures which resulted from the engines high efficiency. For example, at a steady 1 20kph (75mph) the Sprint ST will return over 50mpg (around 5.2 litres per 100km), and on one route used by Triumphs testers the Sprint ST returned 56mpg (around 4.9 litres per 100km) where a leading competitor could only manage 38mpg (7.5 litres per 100km) under identical conditions. The savings to the Sprint ST rider in fuel costs will be welcome of course, and this also considerably expands the bikes touring ability by endowing it with a 200 mile-plus range between refills.
Exhaust emissions also benefit from this efficiency, with the Sprint ST already meeting the tough new EURO 1 emissions requirements due for introduction in 1999. In addition, for the German market it is fitted with a closed loop catalytic converter, which uses three, small diameter catalyst blocks in the downpipes for faster warm up and reduced power loss compared with a single block.
In California the Sprint features an open loop catalyst, which does without the lambda probe of a closed loop system mounted in the exhaust to measure oxygen content.
The fuel injection of the Sprint ST features the same advances that have been applied to Triumphs other injected bikes (1999 specification), which are revised throttle bodies with 5 degree butterflies in place of the previous 12 degree items for improved low rev control, and a new stepper motor in the air bypass system to improve idle stability and for consistent tickover speed.
The result is a superb engine ideally suited to the application. In keeping the power down to 112PS in what is potentially a 130PS engine a relaxed, highly efficient unit has been created with all the inherent character of a triple and a huge spread of torque. The STs engine keeps producing more than 8ONM (601b.ft) from just over 3500rpm right up to 9500rpm with the peak of 95Nm (701b.ft) occurring at just 6000rpm, while the power delivery is smooth and devoid of flat spots right across the rev range.
In keeping with the design brief, the engines development went beyond its power and efficiency. The refinement was taken to new levels by work on the noise, and type of noise, it produced. A side effect of the twin spar frame is the additional sound insulation it provides around the airbox, but even so the design team came up with new, curved intakes which further reduce intake noise levels, while a noise suppression block on the back of the crankcase deadens gear and sprag drive noise.
Established Triumph sophistications were employed on the Sprint too, such as the highly efficient plug top coils which Triumph was among the first to use, along with an ingenious coolant bypass system. This diverts coolant back around the cylinder block while the engine is warming up, rather than simply blocking its route to the radiator as most thermostat-controlled systems do, a procedure which decreases the warm-up time without inducing localised hot spots. The Sprint ST is also fitted with Triumphs EFI diagnostics, which give dealers much faster servicing and fault-finding times.
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