TVR Speed Six engine

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The TVR Speed Six was the name of a normally aspirated straight-6 engine manufactured by TVR, and used in several of their cars including the TVR Tuscan, TVR Cerbera, TVR Tamora, TVR T350 and TVR Sagaris.

The engine's prototypes (sometimes referred to as AJP-6) were designed and delivered by independent engineer Al Melling (the "A" in AJP) as both 3.6 and 4.0 litre units. The key design features were an all alloy block and head, dry sump lubrication system and throttle body electronic fuel injection system. This gave lightweight, extremely fast throttle response and high peak horsepower. The engines that actually went into production however were TVR modified versions of the original AJP-6 prototypes.

The initial 4.0 litre version of the engine as used in the Cerbera produced 350 bhp (261 kW) but later incarnations of the engine have reached claimed outputs of up to 405 bhp (302 kW) in cars like the Tuscan S and Sagaris.

The engine was produced in two different displacements: 3.6, and 4.0. The two versions use the same piston size but different stroke lengths depending on the power needed for the application.

The heads on all versions of the engines are twin-cam 24-valve, with finger follower valve actuation. There is one throttle and injector per cylinder (throttle body EFI), as well as equal length tubular exhaust manifolds. In addition, the engine is canted 30 degrees to the left and the dry sump lubrication system enables the engine to be mounted lower in the vehicle chassis.

There have been complaints of durability issues from some users. In some cases these were attributed to faulty components (particularly the finger followers) provided by TVR's parts suppliers and other cases were attributed to user abuse. The engine is claimed to be extremely sensitive to being revved hard without being allowed to warm up fully first, also, its dry sump oil system can make it difficult for new owners to accurately judge the level of oil in the reservoir and any engine run without adequate lubrication can be subject to mechanical damage.

TVR developed it into the limited-production V12 Speed Twelve racing engine.