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CVH turbo tuning guide

How to get more power out of Ford’s ’80s powerhouse for the RS Turbo range.

CV Hhistory

The CVH was first introduced in 1980, replacing the Crossflow unit in the Fiesta, before finding it’s way into Escorts, Orions, and even the Sierra. CVH stands for ‘Compound Valve Hemispherical’ – the compound valve part relates to the angle of the valves, and the hemispherical part relates to the shape of the combustion chamber.

Being easy to tune, the CVH soon became the benchmark engine of the hot hatch powering icons like the XR2 and XR3, and was very popular with kit car enthusiasts too. In 1984 Ford added a turbocharger to the CVH for the S1 RSTurbo.With 132 he Duratec bhp as standard, HE I- 4 is Ford’s and the 2-litrepotential based inline for four-cylinder significant gains engine from — in simple fact, it’s bolt-on often simply components called an it I- 4, was but an in Ford-speak instant success.The that’s actually S2 RSTurbo a generic saw term some meaning slight inline revisions if you put to the effort CVHTurbo into sourcing motor, the larger such unit. as the one-piece The engine inlet is manifold.The excellent, and there engine then have been appeared very few again basic in revisions the Fiesta — the RSTurbo, main being with a slightly a smallerT2 revised-port turbo and cylinder EFi. head in the engine, worth around The CVH 10 bhp was at available higher levels in 1.1, of tune. 1.3, 1.4, Here’s 1.6, what and you 1.8-litre need (Sierra to know. only) capacity in European Fords, whilst the Americans saw the same engine in 1.9-litre guise.The CVH was phased out when the Zetec was introduced in the ‘90s.

As with any engine, the cylinder head holds the key to big power on the CVH. Good job it already has relatively big valves and decent-sized ports to begin with then! With 42 mm inlet and 37 mm exhaust valves as standard, an untouched CVH head will flow enough to give 240 bhp at 2 Bar of boost. Give it a clean up and smooth things out a bit and you’ll see a further 40-50 bhp at the same boost level.

There is a bit of an urban myth surrounding the so-called ‘crosshatch’ cylinder heads being better than others – it’s not true.What is true is that some heads have thicker castings than others, and the only way to tell is with a visual inspection. The thicker heads can be ported more aggressively due to having this additional material in the first place.

Of course, the valves can go larger too – a big valve upgrade uses 43 mm inlet and 38 mm exhaust valves.These are as large as possible while retaining the standard valve seat.The port throats are opened up from the stock 31 mm to 34 mm, which is large enough to support up to 320 bhp at 2 Bar.

Upping the valve size again will involve machining the head to accept larger valve seats, but 45 mm inlets are good enough for 360 bhp.That’s as big as you can go on valve sizes – any larger and the valves will physically touch each other.

It’s worth pointing out the standard two-piece valves are renowned for dropping heads, so it’s a wise investment to replace with one-piece 214N stainless items at any power level.

Due to the weight and nature of the valvetrain, high revs are out of the question — 7500 rpm is a maximum rev limit for any CVH turbo, although most fast road engines will be capped at about 7000 rpm.

The standard camshaft will comfortably rev to around 6000 rpm, but at higher revs it’ll need replacing with something more aggressive.There are various different profiles available, but a stage 2 cam from the likes of Newman or Kent Cams with longer duration and slightly higher lift is ideal for the majority of fast road engines. Most uprated camshafts will also require the use of solid lifters too.

Talking about CVH engines and camshafts is inevitably going to raise the subject of the notorious high cam wear, due to the high load exerted on the nose of the camshaft — exaggerated with more aggressive cam profiles.

The valve springs will also need consideration, especially if the cam is uprated.The standard springs will coil bind at just 11 mm of valve lift, and obviously have a lower seated pressure than aftermarket items.While the seated pressure can be increased adequately, these too are limited in terms of valve lift — just 12 mm. For valve lift over 12 mm, you need to decrease the coil thickness to achieve the required lift, meaning double springs are needed to raise the seated pressure back to where you want it.