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Ford Cosworth YB Turbo Tuning Guide

Ford Cosworth YB Turbo engine

An incredibly famous engine, the Cosworth YB Turbo actually began life in 1984 as a N/A Cosworth YAA concept. However, the turbo version was launched in the 1986, 3 door Sierra with 204bhp. The infamous RS500 version of the same car followed in 1987 with 225bhp, a bigger T4 turbo, eight injectors (only four connected) and an engine designation of YBD.

Perhaps the most plentiful Sierra, the Sapphire hit the roads between 1988-89 with a 4x4 version being produced from 1990-92. The engine was subsequently available in two versions for this latter car – The YBJ, which incorporated many of the RS500 motorsport type revisions, plus the green cam covered YBG, meant for the US emissions sensitive market. This had three cats, closed loop lambda control and ran on 95 octane unleaded.

Finally the Escort Cosworth took over from 1992 with the big turbo YBT engine, featuring a T34 and four wheel drive, whilst the series came to a halt with the introduction of the T25, small turbo Escort between 1994-96. This also featured Ford EEC IV management, with wasted spark ignition, twin coils, a different series of injectors and a unique black cam cover.

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+.