British Leyland was keen to update the old A-series design in the 1970s. However, attempts at replacement, including an aborted early-70s British Leyland 'K engine' (unrelated to the later Rover K series) and an
OHC version of the A series, ended in failure. During the development of what was to become the
Austin Metro, engineers tested the A series against its more modern rivals and found that it still offered competitive (or even class-leading)
fuel economy and torque for its size. While in the 1970s the A series had begun to seem dated against a new generation of high-revving
overhead cam engines, by the end of the decade a new emphasis on good economy and high torque outputs at low speeds meant that the A series's inherent design was still well up to market demands. Given this, and the lack of funds to develop an all-new power unit, it was decided to upgrade the A-series unit at a cost of £30 million. The result was the 'A-Plus' Series of engines. Available in , the A-Plus had stronger engine blocks and cranks, lighter pistons and improved piston rings, Spring loaded tensioner units for the
timing chain and other detail changes to increase the service interval of the engine (from ). More modern SU Carburettors and revised
manifold designs allowed for small improvements in power without any decrease in torque or fuel economy. Many of the improvements learnt from the Cooper-tuned units were also incorporated, with A-Plus engines having a generally higher standard of metallurgy on all units, where previously only the highest-tuned engines were upgraded in this way. This made the A-Plus engines generally longer-lived than the standard A series, which had a life between major rebuilds of around in normal service. Studies were made into upgrading the engine to use five main
crankshaft bearings but the standard three-bearing crank had proven reliable even in high states of tune and at high engine speeds, so it was not deemed worth the extra funding. The new engines received distinctive 'A+' branding on their rocker covers and the blocks and heads were colour-coded for the different capacities: yellow for and red for engines.
998 Plus The A-Plus version of the motor was produced from 1980 to 1992. Applications:
1275 Plus The larger engine was also given the "A-Plus" treatment. This lasted from 1980 to 2000, making it the last of the A-series line.
1275 Turbo To allow the
MG Metro to compete with larger, more powerful
hot hatchbacks a
turbocharged version of the A-Plus was developed with the assistance of
Lotus Engineering. A
Garrett T3 turbocharger was fitted along with a unique SU carburettor with an automatic pressure-regulated fuel system. The engine block, cylinder head, pistons, crankshaft and valves were all modified from the standard A-Plus engines. The turbocharger was fitted with an advanced two-stage boost control system which only allowed full boost to be achieved at engine speeds above 4000 rpmthis was to prevent damage to the sump-mounted four-speed
gearbox, the design of which dated back to the early 1950s and could not reliably cope with the high torque output of the Turbo engine at low speeds. The quoted power for the A-Plus Turbo was although in practice the tune could vary from car to car and, because the engine was not
intercooled power varied significantly depending on the weather. The MG Metro Turbo was entered in the
British Touring Car Championship in 1983 and 1984, with the tuned engines producing in excess of . Turbo versions lasted from 1983 to 1990. Applications: • 1983–89
MG Metro Turbo, at 6130 rpm and at 2650 rpm • 1989–90
Mini ERA Turbo, at 6130 rpm and at 3600 rpm
1275 MPi A special "twin-port injection" version of the engine was developed by Rover engineer, Mike Theaker. It was the last A-series variant, produced from 1997 to 2000. Few changes were made to ensure the engine complies with Euro 2 (later Euro 3) emission standard, such as adding a 3-way catalytic converter and making it twin-point injection, the engine also receive changes with ignition system by having a
wasted spark instead of the distributor. For the Japanese domestic market the engine maintained the single-point injection version of the engine and the radiator is still on the side due to the space constraint for the air conditioner component. Applications • 1997–2000
Rover Mini MPi 1.3i (TPi), at 5500 rpm and at 3000 rpm
JOHN COOPER GARAGES During the 1990s Mini Cooper revival, John Cooper Garages offered a number of factory-approved "Cooper S" and "Cooper Si" upgrades to the standard Coopers. The conversions came with a full Rover warranty, and could initially be fitted by any franchised Rover dealer. • S pack (carb) • 1st Si pack (Spi) • 2nd Si pack (Spi) • 3rd Si pack (Spi) • 1997 Si pack (Mpi) @ 5500rpm • 1999 Si pack (Mpi) @ 6000rpm == Diesel version ==