Mercury Marine, manufacturer of MerCruiser, is a popular manufacturer of marine engines. The Alpha One 4.3-litre V-6 is the mating of either of the two MerCruiser 4.3-litre engines with Mercury Marine's Alpha One sterndrive power delivery system. The engine is available in two versions: the MPI and the TKS. Both are among the many MerCruiser engines compatible with the Alpha One sterndrive system. When mated, the system is commonly referred to as an "inboard/outbord" because unlike an outboard engine, the engine is mounted inside the boat, but the drive system is mounted on the stern.
TKS 4.3L V-6
Both the TKS and MPI MerCruisers use the same 4.3-litre V-6 engine block. With a modest 9.4:1 compression ratio, it will run on 87 octane pump gas. The TKS delivers 220 horsepower at 4,400 to 4,800rpm. The primary difference between the two engines is their aspiration. The TKS uses a multi-port fuel injection system. With all other components and specifications being the same, the TKS's fuel injection system provides slightly more head flow and better aspiration, delivering more power and fuel economy.
MPI 4.3L V-6
Mercury Marine's MerCruiser MPI version, is identical at its core. It breathes through a single two-barrel carburettor, resulting in a slightly lower maximum output of 190 horsepower at the 4,400 to 4,800rpm range. Carburettors by nature are necessarily inferior in their power production than fuel injection, though the power deliver of an electronically controlled fuel injection provides generally superior power delivery and responsiveness throughout the rev range. MerCruiser V-6 options are primarily about price with the carburetted MPI version saving you some money but not delivering quite the same performance.
Alpha One Drive
The Alpha One inboard/outboard sterndrive system is reported by MerCruiser to be the most popular system of its kind in the world. The Alpha One is an engineering alternative to the outboard engine where the direction of the propeller thrust is moved along with the entire engine. It's an alternative to other inboard drive systems where there is a propeller shaft and rudders. The Alpha One mates to the engine, transmitting power to a propeller unit on the aft-end of the vessel which is steerable by way of a universal joint. The Alpha One system allows the propeller (and boat) to be steered independent of the motor, without rudders. It can safely transmit up to 300 horsepower.