Reinforced exhaust valves Audi R8 V8 4.2 FSI BYH CNDA

Audi engines covered

A 4.2 litre V8 with direct injection and four valves per cylinder, the FSI V8 of the first generation Audi R8 exists under two engine codes: BYH, 420 hp, in the coupé from 2007 to 2010, then CNDA, 430 hp, in the coupé and the Spyder from 2010 to 2015.

It has 16 exhaust valves, two per cylinder. The versions offered start from the makers' standard size, with a 28 mm head, a 5.96 to 5.97 mm stem and a length of 101.8 to 102 mm, held by single or 3-groove collets depending on the brand. Designed for production power, the original valves are quickly pushed to their limit once tuning raises the load, the revs or the gas temperature.

SUPERTECH and FERREA reinforced exhaust valves

The exhaust valve lets the burnt gases out on every cycle. The metal of its head reaches 760 to 870 °C on a naturally aspirated engine, and 1,000 °C and more with forced induction. About 75 % of that heat leaves through the seat and 20 % through the guide. Yet steel quickly loses strength as it heats up: an EV8 family valve steel, used here as a reference, still holds 550 MPa at 600 °C, but only 300 MPa at 800 °C. Rising load, revs and boost pressure make the head hotter, so it fatigues, distorts and eventually stops sealing.

Reinforced valves use materials made for these temperatures. All the SUPERTECH versions offered here are in Inconel, a nickel base superalloy that keeps 860 MPa at 730 °C and still 554 MPa around 815 °C, about 85 % more than EV8 steel beyond 800 °C; one of them has a hollow stem filled with sodium, which carries heat from the head to the stem and the guide. FERREA offers its Super Alloy, a nickel base alloy intended for boosted engines. The SUPERTECH valves get a polished head, the FERREA valves a 3-groove stem that keeps the production setup.

Versions at +1 mm and +2 mm complete the range: only the head grows, from 28 to 29 or 30 mm. The burnt gases leave the cylinder faster, which then takes in fresh charge more easily and helps the power gain. They require exhaust seats machined to the new size.

Exhaust valve technical specifications

Valve fitting

Each valve is fitted with collets matching its groove: KPR-6S-7 for the single groove SUPERTECH valves, 3-groove collets for the FERREA valves. Collets made for three grooves never hold a single groove valve.

A +1 or +2 mm head needs exhaust seats machined to that size: plan a visit to the machine shop.

The stem slides in the guide: measure its clearance and replace the 16 exhaust valve stem seals at every cylinder head rebuild.

Technical guide

Our brands

	SUPERTECH, which grew out of Silicon Valley, has been designing valves, springs, titanium retainers and guides for racing for more than thirty years. Each valve, in stainless steel, titanium or Inconel, is drawn for a given engine and refined with drag, rally and circuit engine builders.
	FERREA Racing Components, launched in 1978 by Horacio Ferrea and Daniel Urrutia, makes its valves in Florida and Argentina, from stainless steel to nickel base superalloys and titanium. Engine builders all over the world, from NASCAR to drag racing, fit its parts.

How to choose

Under the retainer, the collets sit in the groove or grooves of the stem and hold the valve. With one groove or three, the valve is not held in the same way, and that choice decides what you gain from it.

When reinforced valves become necessary

• Higher lift camshafts or stiffer valve springs
• Raised maximum engine speed
• Fitting a turbocharger or supercharger (Inconel version recommended)
• Cylinder head rebuild on a circuit, drift or rally engine
• Original valves marked, worn or already reworked

Vehicle compatibility

OEM part number (exhaust valve):

Don't forget the inlet valves

A rebuilt 4.2 FSI V8 cylinder head goes back together with new parts: replace the inlet valves and the valve stem seals at the same time as the exhaust valves.