Reinforced exhaust valves Toyota GT86 4U-GSE

Toyota engines covered

The 4U-GSE is the 2 litre, 16-valve flat four fitted to the Toyota GT86 (ZN6); Subaru calls it FA20D. Mounted low in the body, it revs high and is the base for many naturally aspirated or forced induction builds.

Each cylinder has two exhaust valves, 8 per engine, with a 29 mm head and a 5.45 mm stem. Two lengths followed each other depending on model year: 95.15 to 95.3 mm on the first cars, 97.6 to 97.7 mm afterwards. These valves take the burnt gases as they leave the chamber, hotter as load and rpm rise.

SUPERTECH and FERREA reinforced exhaust valves

Naturally aspirated, the metal of an exhaust valve head reaches 760 to 870 °C; with a turbo or a supercharger it goes beyond 1,000 °C. The head gives about 75 % of its heat to the seat and 20 % to the guide. An EV8 family steel holds 550 MPa at 600 °C, but only 300 MPa at 800 °C: beyond that the head distorts, fatigues and ends up sealing poorly.

FERREA offers two ranges: Competition Plus in Super Alloy, a nickel-based alloy quoted 20 % stronger when hot with a seat that lasts 25 % longer, and the 6000 series in special alloy. 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 % better than the reference steel near 800 °C, the material to choose for a turbocharged engine.

At +1 mm oversize the head grows to 30 mm with the same stem and length: the flow area at the seat increases, burnt gases leave faster, with 10 to 12 cfm more flow per millimetre of head, and the 8 exhaust seats are machined to the new diameter.

Exhaust valve technical specifications

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

Valve fitting

The collets must match the groove of the chosen valve: check them when refitting the springs and replace them if they are marked.

A 29 mm head sits on the exhaust seats at their factory size; a 30 mm head needs the 8 seats machined by the workshop.

Choose the length from the valves removed: 95.15 to 95.3 mm or 97.6 to 97.7 mm, depending on the cylinder head version.

Technical guide

Our brands

	SUPERTECH Performance, in California, has designed valves and valvetrain parts for racing for more than thirty years. On the GT86 it uses Inconel for its exhaust valves, at standard size in both lengths and at +1 mm in the long version.
	FERREA, founded in 1978, makes its valves in Florida and Argentina. For the GT86 it offers its Competition Plus in Super Alloy in both lengths and its 6000 series in special alloy in the long version, at standard size as well as +1 mm.

How to choose

Three criteria separate the nine versions: size, length and material.

When reinforced valves become necessary

• Turbo or supercharger conversion (Inconel or Super Alloy version recommended)
• More aggressive camshafts or raised rev limit
• Track, drift or hill climb use
• Cylinder head rebuild with burnt or distorted exhaust valves

Vehicle compatibility

OEM part number (exhaust valve):

Don't forget the inlet valves

With the 4U-GSE cylinder head off, take the opportunity to replace the inlet valves and the valve stem seals as well.