Reinforced inlet valves AUDI S4 RS6 A8 4.2 40V BHF BCY BFM BGK

AUDI engines covered

Audi's 4.2 litre V8 with five valves per cylinder, known as the 40V, powers the B6 and B7 S4 saloon, Avant and cabriolet (BHF, 344 hp) from 2003 to 2009, the twin-turbo RS6 C5 saloon and Avant (BCY, 450 hp) from 2002 to 2005, and the A8 D3 4.2 quattro (BFM and BGK, 335 hp) from 2002 to 2010.

Each engine has 24 inlet valves, three per cylinder, operated by hydraulic tappets. Audi part 077 109 601 Q is 96.5 mm long and is fitted with valve stem seal 036 109 675 A. Higher revs, sharper camshafts or more boost on the RS6: every upgrade increases the impacts and heat these small valves take.

SUPERTECH and FERREA reinforced inlet valves

Set in the stream of fresh air, the inlet valve of the 4.2 40V V8 rises and slams back onto its seat thousands of times a minute, its stem constantly sliding in the guide; its head lives between 400 and 550 °C. In that bracket an everyday chrome-silicon steel falls from 500 MPa at 500 °C to 250 MPa at 600 °C, half its strength gone. A worn-out head ends up warping, sinks into its seat and lets compression slip away; lift, spring stiffness, revs and boost pressure add further to these loads.

The SUPERTECH AIVN-1206S comes from machined stainless steel that is then black nitrided: once hardened, the stem limits friction against its guide and takes longer to wear, an asset on this 40 valve V8 that loves revs. Its single groove, wider than usual, takes dedicated collets that clamp it without piling up notches. Lengthwise it keeps the Audi figure and slots into the standard guides.

Its head diameter rises to 27.90 mm, 1 mm more than the Audi part, while length stays at the factory figure. The opening offered to the air widens, filling improves and power with it, as long as all 24 seats on the inlet side get taken to the new diameter.

Inlet valve technical specification

Fitting details

With a single groove, the SUPERTECH valve is fitted with the KPR-6S-7 single groove collets the manufacturer specifies for this part number; the original collets are not suitable.

At 27.90 mm the head exceeds the factory size: the 24 inlet seats are machined to this diameter before reassembly.

The hydraulic tappets take up the clearance on their own: no adjustment is needed after the valves are replaced.

Technical guide

The brand offered

SUPERTECH, a Californian firm from San Jose, has been designing valvetrains for competition engines for more than thirty years. Each reference is drawn for its engine, screened with ultrasound, X-rays and laser, then put to the test with engine builders, from track to drag strip.

How to choose

A groove is a recess machined into the stem tip; the collets lodge there to keep the retainer in place, shaped to the groove count. On this V8: one size, one groove.

When reinforced valves become necessary

• Higher cam lift or noticeably harder springs
• Fuel cut moved beyond the factory one
• Boost pressure increased on the twin-turbo RS6
• Heads rebuilt for the track or hill climbs
• Fatigued stock valves, seats recut once before

Compatible vehicles

OEM part number (inlet valve): 077 109 601 Q

Related products

While the heads of the 4.2 40V V8 remain off, change straight away the exhaust valves as well as the inlet stem seals designed for this engine.