Reinforced inlet valves FORD Sierra Escort RS Cosworth N5B

FORD engines covered

The N5B is the 2.0 litre Cosworth four-cylinder with 16 valves and twin overhead camshafts, built on a Ford block and turbocharged. It delivers 204 hp in the Sierra RS Cosworth from 1985 to 1990 and also powers the Escort RS Cosworth.

The engine has 8 inlet valves with a 6.95 mm stem. More boost, sharper camshafts or a higher rev limit load them far beyond the original tune.

FERREA reinforced inlet valves

In the Ford RS Cosworth (Sierra, Escort), the N5B works 8 inlet valves: the cam pushes each one down to admit the pressurised inlet charge, then the valve drops back with a sharp blow onto its seat face, its stem sliding endlessly deep in the guide. Once the 2 litre is spinning high, the movement exceeds twenty repeats every second. The part sits between 400 and 550 °C; across that interval, the chrome-silicon usually found in stock parts falls from 500 MPa at 500 °C to 250 MPa at 600 °C, losing 50 % of its strength as heat builds, and raised boost adds to this load further.

Both part numbers offered belong to FERREA's 6000 series, in EV8 stainless steel paired with a hard chrome stem. This steel keeps 650 MPa at 500 °C and still 550 MPa at 600 °C, which is 30 % then 120 % extra strength compared with the original steel at the same temperatures. Hard chroming makes the stem surface more resistant to guide friction and limits wear, an asset on a turbo engine spending long minutes at full load on stages or circuit.

The F6747*8 keeps the 35.12 mm standard head; the F6749*8 takes it to 36.12 mm, the +1 mm oversize, with the 6.95 mm stem and 105.44 mm length unchanged. That extra millimetre widens the opening left for the gases against the seat: the cylinders breathe better and the N5B gains power from it, provided a workshop has first recut the 8 inlet seats to 36.12 mm.

Inlet valve technical specification

Stem tip: 1.6 mm.

Fitting details

With the +1 mm size, the 8 inlet seats are cut to 36.12 mm; at standard size they keep their diameter.

Both part numbers have a 6.95 mm stem and a length of 105.44 mm.

Technical guide

The brand offered

FERREA Racing Components dates from 1978 and the Florida city of Fort Lauderdale, founded by a duo of Argentine-born engine builders. Every valve is forged as one piece from bar, then finished entirely on numerical machines; it runs in NASCAR as well as dragster engines.

How to choose

The groove, machined into the stem end, supports the collets locking the retainer; on this page only one thing differs between the two sets: head size.

When reinforced valves become necessary

• Boost raised past the factory setting
• Reprofiled camshafts or uprated valve springs
• Red line moved well beyond stock
• Head prepared for historic rally or track use
• Tired factory valves or seats reground once

Compatible vehicles

Also consider the exhaust valves

To rebuild the whole N5B head, also change its 8 exhaust valves, which we also sell reinforced; you reach them through the next button: