Within the YB range of Cosworth engines there are two distinct variants. These are the 2wd and 4X4 heads. The main difference between these two types of heads are in the combustion chamber shape and volume (smaller on the 4X4). The porting and valves are identical in size on all versions of cylinder heads meaning all heads have the same restrictions and offer the same tuning potential. Std valve sizes are 35mm inlet and 31mm exhaust and use a sodium cooled exhaust valve as std. 

With 2wd heads the general rule of thumb is later the better. Early 3dr heads are best avoided allthough it is possible to weld and machine a 3dr head so that it is converted to late 2wd spec. The easiest way to identify the early 2wd head is by the 2 bolt thermostat housing flange, where as late 2wd heads use a 3 bolt flange as found on the 4X4 heads. All 2wd heads however have a different cooling jacket (termed "open") around the exhaust ports to the 4X4 head (termed "closed") and is less "stable" than the 4X4 type and prone to water leakage under the exhaust manifold. Likewise the exhaust manifold gasket face is smaller on the 2wd head and again inferior in design to the 4X4 head.

However provided your 2wd head is in good rot free condition and above minimum height of 138.63mm it can certainly be successfully to use one of these heads on any level of tune, so is not a necessity to change to 4X4 spec.

If your head has been skimmed below the minimum 138.63mm there are ways around this to avoid scrapping the head and advise you email me for details, although I must advise that in the long run it is easier to find a good usable head in the first place.

Although there are many different specifications of head available, for your chosen spec of engine I have categorised 3 general levels of head that  I most commonly use:

Stage 1: This is essentially a fully reconditioned head featuring new bronze valve guides, stem seals, multi angle valve seats, refurbished and recut valves, a light port to remove all casting flash and original machining and essentially gives you an as new head suitable for use up to 400bhp.

Stage 2: 400bhp+, This head has all the features of the stage 1 but how has enlarged inlet/exhaust ports and is more commonly known as a "low lag 400" head. It is used on all my 400+ engines and is suitable for power up to 500bhp with the correct turbo. (e.g. T4). I use 2 different types of valve spring, a single that allows valve lift to 9.5mm and a double item that allows valve lift to 11.5mm. Cam choice should be made based on these factors as well as the intended power output, characteristics and obviously the rest of the engine specification.

Stage3: Touring car spec, This head is appropriately named as it is similar in spec to the original touring car heads. Featuring larger ports (26 - 27mm) than the previous head this spec is advised for engines requiring in excess of 500bhp.

Another area of great interest is camshaft choice and I do of course use a variety of camshafts and would advise you email me for advice on this topic rather than list out all the options in this section.

Picture : Cosworth Cylinder Head

Picture : Cosworth Cylinder Head combustion chamber