A straight-seven engine or inline-seven engine is a straight engine with seven cylinders. Wärtsilä, with their RTA96-C, and MAN Diesel produce crosshead two-stroke diesel engines in this configuration. Wärtsilä also produces regular trunk engines in this configuration. It is more common in marine applications because marine engines are usually based on a modular design, with individual heads per cylinder.
Only one straight-seven engine for land propulsion is known to be in production, the AGCO Sisu 7-cylinder diesel engine. This engine configuration was chosen because of size, parts commonality, and power range issues. A straight-8 would be too long for the farm machinery application the engine was intended for, whilst a V engine would require a higher investment compared to the expected low sales volume for this power range. The straight-7 configuration is a lower investment because Sisu has reused cylinder heads from their I3 and I4 diesel lineups. This is possible because the cylinder volume, pistons and con rods are identical across the Sisu model range.