Reinforced exhaust valves VAG 4.2 V8 40V Audi S4 allroad Touareg Phaeton

Audi and Volkswagen engines covered

Audi's 4.2 litre V8 with 40 valves, five per cylinder, powers the B6 and B7 generation S4 under the BHF code (344 hp) and the allroad C5 4.2 under the BAS code (299 hp).

Volkswagen fitted the group's 4.2 litre, 40-valve V8 to the first-generation Touareg (AXQ code, 310 hp) and then to the Phaeton 4motion saloon (BGH and BGJ codes, 335 hp).

It has 16 exhaust valves, original part number 077 109 611 S, which supersedes the earlier 079 109 611 B. On such a hard-working V8, fitted to heavy four-wheel-drive cars, they spend long periods in contact with very hot burnt gases.

SUPERTECH reinforced exhaust valves

On this 4.2 litre V8 with five valves per cylinder, the 16 exhaust valves discharge burnt gases on every second crankshaft turn: the head reaches 760 to 870 °C while the engine breathes naturally, and would exceed 1,000 °C once boosted. The seat drains around 75 % of this heat, while 20 % leaves via the guide. As the benchmark adopted for the original part, EV8 steel keeps 550 MPa at 600 °C yet holds only 300 MPa near 800 °C; on a loaded S4, Touareg or Phaeton, the head ends up fatiguing, warping and leaking.

The AEVI-1206S-16 is made of Inconel, a superalloy whose nickel base keeps 860 MPa at 730 °C and still 554 MPa at 815 °C, in the order of 85 % above EV8 near 800 °C. Its stem carries a single groove, gripped over its full height by matching collets.

Offered at +1 mm, it keeps the 5.94 mm stem and 94.8 mm length, but its head grows to 30.9 mm: the outlet area widens, the chamber purges sooner and fills better. For this, the 16 exhaust seats must be machined to that diameter.

Exhaust valve technical specifications

AEVI-1206S: 30.9 mm head (+1 mm), 5.94 mm stem, 94.8 mm length, Inconel, single groove.

Valve fitting

The single-groove stem is fitted with the matching KPR-6S-7 collets: the original collets are not suitable.

The 16 exhaust seats are machined for a 30.9 mm head before fitting, by a machine shop.

Replace the exhaust valve stem seals during the same job and fit all 16 valves from the same set.

Technical guide

Our brand

SUPERTECH Performance has built racing valvetrain parts in California for over three decades: valves, titanium retainers, springs, guides. Stainless, titanium or Inconel, the material follows the use, and every valve, born for one engine, is dialled in with drag, rally and track engine builders.

How to choose

For the 40-valve 4.2 V8s from Audi and VW, one version: the AEVI-1206S-16, in Inconel, 30.9 mm head at +1 mm, single-groove stem. Two prerequisites for fitting: machined seats and single-groove collets:

When reinforced valves become necessary

• Boosted V8, supercharger or turbo (Inconel advised)
• Higher-lift camshafts or uprated springs
• Track use or heavy load sustained while towing
• Burnt or distorted exhaust valves at high mileage
• Rebuild of both heads on an S4, Touareg or Phaeton

Vehicle compatibility

OEM part number (exhaust valve): 077 109 611 S

Don't forget the inlet valves

Once both V8 heads are on the bench, refresh the inlet side too, with its valves and every stem seal on both banks. The part suited to these engines: