TVR Speed Six engine

The TVR Speed Six was the name of a naturally aspirated straight-six engine manufactured from 1999 to 2007 by British car manufacturer TVR, and used in several of their cars including the Tuscan, Cerbera, Tamora, T350, Sagaris and Typhon.

The engine's prototypes (referred to as AJP-6) were designed and delivered by independent engineer Al Melling (the "A" in AJP) as both 3.0 and 3.5 litre units. Many of its key cylinder head design elements (particularly the valvetrain) were first seen in the 1991 Suzuki GSX-R750 (M) motorcycle engine (also a Melling design).

The key design features were an all aluminium alloy block and head, with cast iron cylinder liners, double overhead camshafts, finger follower 24-valve actuation, one throttle and injector per cylinder (throttle-body fuel injection), equal length tubular exhaust manifolds dual 3-way catalytic converters and a dry sump lubrication system allowing the engine to be mounted lower in the vehicle chassis. These features enabled the engine to provide lightweight, compact dimensions, extremely fast throttle response and high peak horsepower.

In order to reduce unit production costs, the engines that actually went into production, called Speed Six, were TVR modified versions of the initial AJP-6 prototypes with 3.6 litres (3,605 cc) and 4.0 litres (3,996 cc) capacities. Prominent modifications were alterations to valve train geometry, a switch from a billet steel crank to cast iron (with a crank damper), different connecting rods, oil filter relocation to the inlet side of the engine, and removal of the exhaust cam oil feed. The two different capacities were achieved through stroke alterations from a con-rod design able to accommodate two different stroke lengths, and different piston crown designs altering the compression ratios. The bore diameters were shared. Pistons were made in Italy by Asso Werke from pre-existing casts, initially designed for the Rotax-Aprilia RSV 1000 engine.