Theturbo

The good news here is that the stock RS Turbo exhaust manifold is good for 300 bhp without even touching it. Some porting will see it support over 400 bhp.

Using the original manifold means you can fit almost any turbo with a T3 flange (disregard the Fiesta RS Turbo manifold as it has a smaller T2 flange). The original T3 turbo can still support impressive increases, but it does need tweaking. The first step is commonly to go for a 55 trim compressor wheel and a 0.48 A/R exhaust housing. This is good for a solid 250 bhp.

The original turbo set up uses an elbow attachment on the exhaust housing, to which the rest of the exhaust system is fitted. This elbow is very restrictive and literally robs power potential. By changing to a Cosworth housing and downpipe the same turbo will support up to 280 bhp. The next step would involve upping to a T34 hybrid with 0.55 exhaust housing (good for 330 bhp) or even a modified T4 turbo for higher bhp levels.

The compound valve angle of the CVH is one of its main characteristics and is what gives many of the engine’s benefits. Unfortunately it is also the cause of one of its biggest drawbacks — the inability to rev.The rocker geometry required to operate the awkwardly angled valves is not suited to high revs.The valvetrain components are also quite heavy, again reducing the ability to rev freely. Most recommend setting the rev limit at around 7000 rpm for a moderately tuned fast road engine.A real screamer of a track engine could potentially raise this limit to around 7500 rpm, but anything above this and there’s a serious risk of valvetrain failure.