Forged connecting rods Audi 4.2L 40v BCY-BRV for forged pistons

The Audi RS6 C5 4.2L 40v BCY / BRV engine

Launched in 2002, the Audi RS6 (type C5) uses a 4.2-litre twin-turbo V8 with 40 valves (5 per cylinder), engine codes BCY and BRV, co-developed with Cosworth Technology. Bore 84.5 mm, stroke 93 mm, displacement 4172 cm³. Two KKK/Borg Warner K04 turbochargers, one per cylinder bank, push output to 450 hp (331 kW) on the RS6 quattro (BCY) and 480 hp (353 kW) on the RS6 plus quattro (BRV, Avant only).

On such a highly stressed block, the original sintered-steel connecting rods become the weak point as soon as displacement or boost pressure increases. NSB Concept offers a set of 8 forged ZRP I-beam connecting rods, machined from 4340 high-yield-strength steel, to secure the bottom end on a tuned build.

Technical specifications

Torque and stretch specification

4340 forged steel

Unlike the original sintered-steel rod, the NSB Concept rod is machined from a forged 4340 billet: a chromium-molybdenum alloy, quenched and tempered, offering a markedly higher yield strength and fatigue resistance than the original sintered metal. Forging aligns the grain flow with the load path, improving tension/compression behaviour and service life under repeated cycles, essential once engine speed or boost pressure increases.

How to choose your connecting rod bolts?

Bolt grade selection depends on the targeted power level. Our rods are offered with two ARP grades in 3/8" diameter:

ARP 2000
	Alloy steel bolt rated at 220,000 psi (1517 MPa) tensile strength, suited to roughly up to 200 hp per cylinder: a solid base for a naturally aspirated or moderately boosted engine.
ARP L19
	Alloy steel bolt rated at 260,000 psi (1793 MPa), aimed at heavily boosted engines or high rpm, up to roughly 250 hp per cylinder, with better fatigue resistance under cyclic loads.

Measuring bolt stretch

Connecting rod bolt tightening is controlled by measuring bolt stretch (ARP's recommended method), more accurate than a simple torque wrench reading. A dedicated dial gauge measures the actual stretch of each bolt while tightening, to bring it to the value shown in the table above.

→

Available brands

ZRP is a Greek manufacturer based in Athens, specialised in high-performance forged connecting rods. Each set of 8 rods is weight-matched to within ±1 gram to limit vibration and preserve crankshaft balance. The I-beam profile offers an excellent stiffness-to-weight ratio, suited to high rpm as well as heavily boosted large-displacement engines.

Glossary

1) Small end 2) Small-end diameter 3) Rod beam 4) Rod bolt 5) Big end 6) Rod nut / bolt 7) Rod cap 8) Big-end diameter 9) Center-to-center

Vehicle compatibility

Forged connecting rods: for which disciplines?

A forged connecting rod only makes sense if the rest of the bottom end follows: forged pistons, reinforced rod bolts and, depending on the build level, suitable bearings. On an RS6 C5 base, this type of reinforcement targets engines built for circuit racing, drift, drag, hillclimb, rally or time attack, once boost pressure, rpm or torque exceed the tolerances of the original part. Tuners generally distinguish several stages (Stage 2, Stage 3, Stage 4 and beyond) depending on the extent of the engine modifications; switching to a forged rod becomes relevant once the targeted power or boost pressure exceeds the safety margin of the original part.

A calculated investment

Given the risk of engine damage from a connecting rod failure, investing in a forged rod kit remains modest compared with the cost of a full bottom-end rebuild. It is a safety component for any engine whose power is significantly raised above stock.