Reinforced exhaust valves Subaru BRZ FA20

Subaru engines covered

Under the bonnet of the Subaru BRZ (ZC6), the FA20 is a 2 litre, 16-valve flat four, the same unit Toyota calls 4U-GSE. Its very low centre of gravity has made it a favourite base for tuners, naturally aspirated or with a turbo or supercharger.

The engine has 8 exhaust valves, two per cylinder, with a 29 mm head and a 5.45 mm stem. Their length changed over the model years: 95.15 to 95.3 mm first, then 97.6 to 97.7 mm. Placed at the exit of the combustion chamber, they take the burnt gases at their hottest, especially at full load and high rpm.

SUPERTECH and FERREA reinforced exhaust valves

On an engine without forced induction, the exhaust valve head reaches 760 to 870 °C metal temperature; a turbo or supercharger pushes it beyond 1,000 °C. It cools for about 75 % through its seat and 20 % through its guide. An EV8 family steel offers 550 MPa at 600 °C and only 300 MPa at 800 °C: at that level the head sags, cracks through fatigue and loses its seal.

SUPERTECH makes its valves in Inconel, a nickel-based superalloy that keeps 860 MPa at 730 °C and 554 MPa at 815 °C, about 85 % more than the reference steel near 800 °C: the choice for turbocharged engines. FERREA offers its Competition Plus in Super Alloy, a nickel-based alloy given 20 % more strength when hot and a seat life extended by 25 %, as well as its 6000 series in special alloy.

The +1 mm oversize takes the head to 30 mm, stem and length unchanged: the passage for burnt gases grows, with 10 to 12 cfm more flow per millimetre of head, provided the 8 exhaust seats are machined to that diameter.

Exhaust valve technical specifications

Standard size: F2356P, F2378P, F6347, SEVI-1050 and SEVI-1050-2; +1 mm: F2359P, F2380P, F6348 and SEVI-1052-2. SEVI-1050, F2356P and F2359P are 95.15 or 95.3 mm long, the others 97.6 or 97.7 mm.

Valve fitting

When refitting the springs, check that the collets match the groove of the chosen valve; marked collets are replaced.

The 29 mm head sits on the exhaust seats as they leave the factory; the 30 mm head requires the workshop to machine the 8 seats.

Measure a removed valve to choose the length: 95.15 to 95.3 mm or 97.6 to 97.7 mm depending on the cylinder head.

Technical guide

Our brands

	SUPERTECH Performance has designed valves and valvetrain parts for competition in California for more than thirty years. For the BRZ its exhaust valves are in Inconel: standard size in short or long length, +1 mm in long length.
	FERREA, founded in 1978, produces its valves in Florida and Argentina. For the BRZ the Competition Plus in Super Alloy comes in both lengths, the 6000 series in special alloy in the long length, each at standard size and +1 mm.

How to choose

The nine versions differ by three criteria: size, length and material.

When reinforced valves become necessary

• Turbo or supercharger fitment (Inconel or Super Alloy version recommended)
• Higher lift camshafts or raised rev limiter
• Track, drift or hill climb
• Cylinder head to rebuild after a burnt or distorted exhaust valve

Vehicle compatibility

OEM part number (exhaust valve):

Don't forget the inlet valves

When the FA20 cylinder head is off, it is the right time to change the inlet valves and the valve stem seals too.