INTERNALS

The stock crankshaft is a very strong unit, and can be used for almost any power level you want to achieve – as can the Zetec crank if you’re using a Zetec bottom end.

The weak links are the pistons, and in particular the con-rods — forged steel con rods should be fitted in any CVH build that’s not intended for standard power.

The standard rods are basically just too measly to take any serious power.The construction and materials used mean they simply bend, or worse still, break in half if you start increasing the pressures exerted on them.

The same can be said for the stock pistons too. Increased boost levels and higher bhp levels certainly don’t help the stock pistons, but the real killer is when you start increasing the revs. At higher engine speeds the con-rod simply tries to pull itself off the bottom of the piston, resulting in cracked pistons.

The standard 8.2:1 CR is too high, because with any meaningful amount of boost it will start to introduce detonation (especially if the mechanical injection is retained). Most tuners prefer to lower the compression ratio to around 7.5:1(ish) depending on the desired characteristics of the engine. It’s worth noting that a variety of displacements can be achieved, but if you want anything other than 1596cc (using 1.6 crank and block), 1720cc (using 1.9 block and 1.6 crank), or 1998cc (using 2.0 Zetec crank and block), then a custom billet crank will be required — adding at least £2000 to any build.