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Ford Cosworth YB series Engine
The YB series of 1,993 cc (121.6 cu in) engines are based on the older Pinto engine block, and were introduced in the road-going Ford Sierra RS Cosworth in 1986 with 204 PS (150 kW; 201 bhp). With 5,000 units built for homologation purposes in Group A, both for rallies and touring cars. Racing versions could develop about 400 hp (298 kW; 406 PS). A limited edition evolution model was introduced in 1987, the RS500, with power now exceeding 550 hp (410 kW; 558 PS) in full racing trim. The RS500 came to dominate touring car racing in its heyday from 1987 to 1992, winning multiple championships and major races in Europe, Japan and Australia. This included wins in the three major races, the Spa 24 Hours held at Spa-Francorchamps in Belgium, the Bathurst 1000 at Mount Panorama in Australia, and the InterTEC 500 at Fuji in Japan.
At the end of its life in Group A in 1992, the Australian Sierra teams were reportedly getting around 600 bhp (447 kW; 608 PS) from the YB engines.
Ford Cosworth YB with Normally Aspirated induction
The various colour cam covers that distinguished each version were as follows: Red: YBB (Sierra Cosworth 2wd, both 3-door and Sapphire), YBD (Sierra RS500), YBJ (Sierra Sapphire 4wd, non cat); Green: YBG (catalyst equipped 4x4 Sierra Sapphire Cosworth); Blue: YBT (large-turbo Escort Cosworth); Silver: YBP (small-turbo Escort Cosworth).
Further evolutions of the YB included a reduced-emissions road version, as well as the block used in the Escort RS Cosworth (which used the Sierra floorpan). The engine stopped being used on new cars in 1997, with the Focus WRC and road-going Focus RS relying on Zetec designs
A upgraded Ford Cosworth YB
The most common engine is the original YBB (3 dr and 2wd Sapphire), which can be easily tuned with chip and turbo modifications to increase the boost level. However, the 4x4 head is the ideal base since the early type has less water jackets and is susceptible to blowing head gaskets with serious hikes in boost.
To begin with, you’ll need to upgrade the actuator to -31 (dash 31) type and upgrade the management chip to increase the fuel and boost level too - this will typically be to around 270/280bhp. We would recommend that you also fit a good stainless exhaust such as our Mongoose range, plus a K&N filter.
After that stage, you need to swap the injectors for 803s – commonly known as Dark Greens. To this you’ll need a different chip again, plus a 3-BAR MAP sensor to up the boost to 19 PSI (1.3 BAR) resulting in approximately 320-330bhp.
Beyond this level, we’d recommend fitting a Group A or multi-shim head gasket and for extra security in high-boost applications, and an ARP stud and nut kit.
However, around this level, the standard Garrett T3 turbo will have reached its limit although there are now several paths to take in turbo choice. These though are always a trade off between turbo lag and driveability – hence why going straight to a T4 isn’t always a good move. Popular choice is to fit an Escort T34 or a hybrid T3 along with a larger intercooler. T38’s are also available although these aren’t an off-the-shelf Garrett unit and are seen more as a hybrid. You should see power potential with this to around 460bhp, whilst the T34 will give you power to around 380bhp.
At this point – and especially if you want to use a T4 with power potential to the touring car levels of 540bhp - the engine needs to be purpose-built to suit. The reason is you’ll need extra head work in terms of porting, different cams (although BD14s are the limit on the street), lower compression ratios and long stud conversion. The trick is making the most of the unit whilst producing power without huge amounts of lag. Once you get to this stage, we can advise you on the best way forward, depending on the type of engine you have.
A different route, and still popular way to tune the YB, is to return it to the original N/A application, which involves raising the compression. For this, we stock Accralite forged pistons to increase the ratio to as much as 12.5:1 although they can be machined to lower the CR since they have raised crowns for this purpose.
On top of this modification, the head needs the ports seriously opening out and for ultimate horsepower applications, larger valves installed. The cams too need swapping for non-turbo profiles although they aren’t designed to work with the standard YB hydraulic lifters and therefore need converting to solid lifter type.
The bottom end is fine for this type of aspiration since the rods and crank are both steel. We would recommend however, that the rod bolts are upgraded for high-revving applications. For ultimate power though, we also stock steel H-section rods. Lastly, you will need to swap the turbo inlet manifold for a twin DCOE type allowing either 45/48 side draughts or throttle body fuel injection. In this form, you should be able to achieve in excess of 225bhp+.
Technical
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Cosworth YB Engine technical details Sierra Cosworth
No. of cylinders Type 4/DOHC
Capacity 1993 cc
Compression ratio 8.0:1
Firing order 1-3-4-2
Minimum octane rating RON 98/95
Ignition system Type IAW
Fuel system Make Weber-Marelli
Fuel System MFI-s
Ignition coil Make Motorcraft
Ignition coil supply voltage with ballast 11V
Primary resistance 0,72-0,88 Ohm
Secondary resistance 4500-7000 Ohm
Distributor Make Marelli
Contact breaker gap/trigger air gap 0.2-0.3mm
Oil temperature for CO test 60°CSpark plugs
Original equipment Motorcraft Type AGPR901R Electrode gap 0.75mm
Bosch Type FR6DP1X Electrode gap 1.0 mm
Champion Type C59C Electrode gap 0.7 mm
NGK Type BCR8ES Electrode gap 0.7 mmCosworth YB Engine technical details Escort Cosworth
No. of cylinders 4/DOHC
Capacity 1993 cc
Compression ratio 8.0:1
Fuel system Makem Weber-Marelli
Ignition coil Make Motorcraft
Firing order 1-3-4-2
Spark plugs Original equipment Motorcraft Type AGPR901R
Electrode gap 0.75mm
Engine Output: 220
Fuel pump delivery pressure 5.0 bar Min
Radiator cap 0.85-1.10 bar
Thermostat opens 88°C
Drive belt size - alternator 9,5x913mm
Service
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Service checks and adjustments Escort Cosworth
Valve clearance -INLET Hydraulic
Valve clearance -EXHAUST Hydraulic
Engine oil grade - normal climate 5W/50 SAE
Engine with filter(s) 3.4 litres
Manual gearbox oil grade 80W SAE
Manual gearbox oil 4/5 speed 2.55 litres
Differential oil grade - rear 90W SAE
Differential oil rear 1.0 litres
Cooling system 7.5litres
Tightening torques
Cylinder head
Stage 1 Tighten 20-25 Nm
Stage 2 Tighten 45-50 Nm
Stage 3 Tighten 180°
Main bearings
Stage 1 44-50 Nm
Stage 2 88-101 Nm
Big end bearings
Stage 1 27-30 Nm
Stage 2 55-60 Nm
Flywheel/driveplate 63-69 Nm
Crankshaft pulley/damper centre bolt 122-135 Nm
Spark plugs 28-33 Nm
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Maintenance
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