Editing TVR Speed Six engine (section)

{{Use dmy dates|date=August 2017}}
{{Use British English|date=August 2017}}
{{Refimprove|date=January 2008}}
{{Infobox automobile engine
| name = TVR Speed Six engine
| image = TVR Cerbera speed six engine.jpg
| caption = Engine installed in a TVR Cerbera
| manufacturer = [[TVR]]
| production = 1999 &ndash; 2007
| configuration = [[Naturally aspirated]] [[Straight-6]]
| block = [[Aluminium alloy]]<ref name="Tuscan">{{cite web
|url=https://www.carfolio.com/specifications/models/car/?car=88594
|website=Carfolio.com
|title=2001 TVR Tuscan S
|date=2013-02-28
|accessdate=2018-09-24}}</ref>
| head = Aluminium alloy<ref name="Tuscan"/>
| displacement = {{convert|3605|cc|L cuin|1|abbr=on}},<ref name="Tamora">{{cite web
|url=https://www.carfolio.com/specifications/models/car/?car=88770
|website=Carfolio.com
|title=2001 TVR Tamora
|date=2013-02-28
|accessdate=2018-09-24}}</ref> {{convert|3996|cc|L cuin|1|abbr=on}}<ref name="Sagaris">{{cite web
|url=https://www.carfolio.com/specifications/models/car/?car=120208
|website=Carfolio.com
|title=2003 TVR Sagaris
|date=2013-02-28
|accessdate=2018-09-24}}</ref>
| bore = {{convert|96|mm|2|abbr=on}}
| stroke = {{convert|83|mm|2|abbr=on}}<ref name="Tamora"/><br/>{{convert|92|mm|2|abbr=on}}
| valvetrain = [[DOHC]] [[Multi-valve#Four valves|4 valves]] per [[Cylinder (engine)|cylinder]]
| power = {{unbulleted list
|{{convert|350|bhp|PS kW|0|abbr=on}} at 6800 rpm<ref name="Cerbera">{{cite web
|url=https://www.carfolio.com/specifications/models/car/?car=30503
|website=Carfolio.com
|title=2000 TVR Cerbera Speed Six
|date=2016-06-05
|accessdate=2018-09-24}}</ref>
|{{convert|390|bhp|PS kW|0|abbr=on}} at 7000 rpm<ref name="Tuscan"/>
|{{convert|406|bhp|PS kW|0|abbr=on}} at 7000-7500 rpm<ref name="Sagaris"/>}}
| torque = {{unbulleted list
|{{convert|290|lbft|0|abbr=on}} at 5500 rpm<ref name="Tamora"/>
|{{convert|310|lbft|0|abbr=on}} at 5250 rpm<ref name="Tuscan"/>
|{{convert|330|lbft|0|abbr=on}} at 5000 rpm<ref name="Cerbera"/>
|{{convert|349|lbft|0|abbr=on}} at 5000 rpm<ref name="Sagaris"/>}}
| compression = 11.0:1, 11.8:1, 12.2:1
| fueltype = [[Petrol engine]]
| fuelsystem = [[Multi-point fuel injection]]
| oilsystem = [[Dry sump]]
| coolingsystem = [[Water cooling (engines)|Water-cooled]]
| designer = [[Al Melling]]
}}

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 [[TVR Tuscan Speed Six|Tuscan]], [[TVR Cerbera|Cerbera]], [[TVR Tamora|Tamora]], [[TVR T350|T350]], [[TVR Sagaris|Sagaris]] and [[TVR Typhon|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.<ref name=Dodds>{{cite book|last1=Dodds|first1=Ralph|title=TVR: Cars of the Peter Wheeler Era|date=31 July 2015|publisher=The Crowood Press Ltd|isbn=978-1847979971}}</ref> Many of its key [[cylinder head]] design elements (particularly the [[valvetrain]]) were first seen in the 1991 [[Suzuki GSX-R750#GSX-R750 (M) 1991|Suzuki GSX-R750 (M)]] motorcycle engine (also a Melling design).

The key design features were an all [[aluminium alloy]] block and head,<ref name="Tuscan"/> with [[cast iron]] [[cylinder liner]]s, [[double overhead camshaft]]s, finger follower 24-valve actuation, one [[throttle]] and injector per cylinder ([[throttle-body fuel injection]]), equal length tubular [[exhaust manifold]]s dual 3-way [[catalytic converter]]s 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.<ref name=Dodds />  

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 {{convert|3605|cc|L|1|order=flip}} and {{convert|3996|cc|L|1|order=flip}} capacities. Prominent modifications were alterations to valve train geometry, a switch from a billet steel [[Crank (mechanism)|crank]] to cast iron (with a crank damper), different [[connecting rod]]s, [[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 ratio]]s. 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. Those casts, refused by Rotax, were modified and used to produce the smaller Speed Six pistons.

Unfortunately, during TVR’s development of the original MCD design, it was decided to remove the drilled lubrication oil-ways from the camshaft centres to the peak of each of the camshaft lobes, resulting in starvation of lubrication and early versions of the Speed Six engine suffering from poor valve-train durability leading to many warranty claims against TVR. 

German and French tuners and owners have, since, re-introduced these oil-ways, returning the motor to its original, efficient and reliable design. 

Other third party development work has also mitigated this issue by using revised material hardness for the cam lobes, finger followers and valve guides. Softer valve springs and valves with thicker stems were also utilised. Engines that have had these modifications performed have also improved durability.

The initial 4.0 litre version of the engine as used in the Cerbera produced {{convert|350|bhp|PS kW|0|abbr=on}} with the final incarnations of the engine having TVR claimed outputs of {{convert|406|bhp|PS kW|0|abbr=on}} in the [[TVR Tuscan Speed Six|Tuscan S]], [[TVR Sagaris|Sagaris]] and [[TVR Typhon|Typhon]] and being the most powerful naturally aspirated straight-six engine in any production road car.

TVR further developed the Speed Six into the limited-production [[V12 engine|V12]] [[TVR Speed Twelve engine|Speed Twelve]] racing engine. TVR also experimented with [[supercharging]] the Speed Six engine for use in the Typhon/T440 model. However this proved unsuccessful due to cooling challenges so the few Typhon/T440 models that made production were instead fitted with standard naturally aspirated 4.0L Speed Six engines.