This gave the Sierra Cosworth instant racing pedigree, and is well deserved.  It earned its racing stripes by using a combination of tried and trusted robustness along with a genuine desire to succeed.

This table is a basic overview of all the Sierra and Escort Cosworths, just to show how they all compare.

  *=5545 examples built, 5000 sold to the public, 500 reserved for RS500, 40 used for racing, 4 RS500 prototypes, 1 kept by Ford.

Engine

The block:

The cast iron block came from the humble OHC Ford Pinto engine, which had powered most Fords since the seventies, and was powering Sierras until 1991, when it was finally succeeded by the CVH and 8 valve DOHC I4.  The 2.0 litre '205' blocks were specially selected at the factory before being shipped to Cosworth - bore sizes were only permitted to be size 2 or 3, this was indicated by a four digit casting on the block near the distributor mounting hole.

The RS500 used a re-inforced 205 block to help keep the 560+ BHP that they would eventually develop in Group A racing, under control.

The modifications used in the RS500's block were carried over to the 4x4 Sapphire's '200' block.  The 200 block was a further development of the YBD block, and is generally used as the basis for big power engines.

The head:

The YB head was cast by Cosworth in aluminium, and carried two overhead camshafts, which actuated 16 valves - 4 per cylinder.  The combustion chamber is of the pent-roof type, with the spark plug centrally mounted in the chamber.

There are two versions of the head - the 2 wheel drive version, and the 4 wheel drive version.  The 4 wheel drive version had no provision for a turbo vibration damper, as the redesign eliminated the need for one.  4 wheel drive heads are also used as the basis for big power engines as they're typically stronger than 2 wheel drive ones.

The exhaust manifolds are different between the 2wd and 4x4 engines, as they are designed for slightly different purposes.  The 2wd manifold is designed for high power at the top end, while the 4x4 manifold is designed to improve throttle response and decrease turbo spool time (turbo lag).

Did you know?

• The fuel pump on the Escort Cosworth was the same pump used on the Orion 1600i Ghia, instead of the more suitable Bosch 941 unit seen on the Sierra Cosworths.  The Orion unit was (just) adequate for the Orion, but not really suitable for the Cosworth's high flow fuel demands.  It's safe to say that most have probably been replaced with Bosch 941 or high pressure Bosch 044 units due to failure or simply because of the original's inadequacy.

• Sierra Cosworths used a Bosch 941 fuel pump, which is perfectly adequate for delivering enough fuel for 350bhp
  

• Leather interiors were not an option until 1989.

• The drivers' outer seat bolster often wears out quicker than the passengers one - these seats are actually interchangeable.  To install a passenger seat on the drivers side, attach it to the drivers seat sub-frame before installation.

• The Sierra Cosworth should have been run by Ford's own EEC IV engine management system, however, Cosworth were doing alot of work with Weber and Marelli.  In order to maintain their relationship with Weber/Marelli, Cosworth insisted that the management system be theirs, instead of Ford's.  Ford eventually got their way with the small turbo Escort, which is EEC IV controlled (the EEC IV derivative code is COSY).

• The water pump in the YB engine is the same pump found in the 1985 onwards 2.0 OHC (Pinto) engine.

• The 3 door Cosworths (RS500 included) have better designed Track Control Arms than the Sapphires that succeeded them.  The arms were designed for Group A racing, Sapphires weren't.
  

• The only Sapphires with bonnet vents were 4 wheel drive.  The vents were removed from the 2 wheel drive Sapphire to fit in with the more executive image of the Sapphire.  After it transpired that many were suffering from overheating, the designers added bonnet vents to the 4x4 Sapphire Cosworth to aid cooling.  As all Crystal Blue Sapphires are 2 wheel drive, getting a 4x4 bonnet on a Crystal Blue Sapphire can be difficult as they need to be painted - the other factory colours that were carried over to the 4x4 are easier to match.

• ABS ECUs from 4x4 and 2wd Cosworths cannot be mixed and matched.  Apart from having slightly different braking hardware at the wheels, the ABS wiring loom is different between the two; the ECUs are wired slightly differently and will pop if they're put in the wrong loom.  4x4 ABS units are easily identifiable by a big 4X4 sticker.  The 2wd loom has an orange relay in position VII in the fuse box, while the 4x4 does not.

• There are two versions of the L8 ECU - lambda enabled and non-lambda enabled.  The lambda enabled ECU carries a green sticker.

• The ABS system used in the Cosworth range is the Teves Mark II system, also found in ABS equiped Sierras, Mark 3 Granadas and Scorpios.  Later Granadas and Scorpios used the Teves Mark IV and Mark 20 ABS systems.  The Teves Mk II system is also found in many other vehicles of the time.

• The Sierra Sapphire Cosworth, is actually known by Ford as the Sierra RS Cosworth.  What's printed on the log book is whatever the original dealer wrote on the registration form.  The only appearance of 'Sapphire' is a small badge on the rear door quarter panels.  Ford's differentiation between the 3 door and Sapphire is the 'hatchback' and 'notchback', respectively.

• Small Turbo and Large Turbo Escort Cosworths use the same boost control solenoid: a Lektron device, which can operate at 100hz as apposed to the SEM 25hz device on the Sierras.  The Lektron valve is 2 port as apposed to 3 port - an external t-piece is used as apposed to internal on the SEM valves.

• Crystal Blue was one of the three original Sapphire Cosworth colours, the other two were Mercury Grey and Diamond White.

• Crystal Blue Sapphires appear to have only been built between January 1988 and July 1988 - if you have one that's outside these dates, I'd love to hear from you!