TVR Speed Six engine

"Speed Six" redirects here. For the Ruger revolver, see Ruger Speed Six.

TVR Speed Six engine

Manufacturer	TVR
Production	1999 – 2007
Configuration	Straight-6

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. It is reputed that many of its key design elements (particularly the valvetrain) were first seen in the 1991 Suzuki GSX-R750M motorcycle engine, which was also a Melling designed unit.

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. Prominent modifications were a switch from a billet steel crank to cast iron and to remove an oilway from the exhaust side of the cylinder head (the original Melling engine design had an oilway on both the inlet and exhaust sides). It was suggested that this caused poor lubrication and cooling to the head around cylinder 6 leading to premature valvegear failures, detonation and a reputation for poor reliability. Subsequent development work has shown that the primary cause was actually mismatched surface hardnesses between the cam lobes and the finger followers resulting in accelerated wear rates to the finger followers. Later versions of the engine and aftermarket components have since eliminated these problems.

It is not clear exactly why these modifications were done, however amongst rumors of a soured business relationship between Melling and TVR, it is believed that the primary reason was to reduce the unit production costs.

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 specialists TVR Power now offer core exchange engines [1] taken out to 4.3 and 4.5 litres, giving more power.

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