Volvo Revised N (RN) Modular Engine

Introduction

Volvo’s ‘Revised N’ (RN) engines were a range of modular inline four-, five- and six-cylinder engines that were manufactured in Skövde, Sweden. The five- and six-cylinder RN engines were first introduced in late 1998 for the Volvo S80 and all RN engines were transversely mounted (in contrast, the preceding six-cylinder N Series engines were longitudinally mounted). As such, 90 per cent of main components for the six-cylinder RN engines were new; for five-cylinder RN engines, 50-90 per cent of the components were new. Relative to the N Series engines, however, almost all moving parts for the RN engines were new.

As per the table below, the RN engines were subsequently introduced in the Volvo S40, V40, S60, V70 and C70. For the Volvo S40/V40 Phase II (introduced in 2000), all four-cylinder engines – except a 1.8-litre direct injection petrol engine sourced from Mitsubishi – were members of Volvo’s RN family.

Commonalities with N Series engines

The structure of the RN engines was the same the N Series and consisted of (top to bottom) a camshaft housing, cylinder head, cylinder block, lower crankcase and oil sump. Like the N Series engines, the RN engines also had:

• A cylinder block and lower crankcase manufactured from high-pressure die-cast aluminium, featuring a reinforcing ribbed structure and cast in oil channels and coolant ducts;
• A chill-cast aluminium alloy cylinder head;
• Grey iron cylinder liners that were cast-in during the die-cast process for the cylinder block;
• A forged crankshaft and forged connecting rods;
• Aluminium pistons with cast-in steel expansion control. The piston ring package consisted of two compression rings and one oil scraper ring;
• Double overhead camshafts driven by a toothed belt with automatic belt tensioner; and,
• Pent-roof combustion chambers.

Commonalities with N Series engines

New features for the RN engines included:

• Continuously Variable Valve Timing (CVVT): initially, naturally aspirated RN engines had CVVT for the intake cam and turbocharged engines had CVVT for the exhaust cam, though both had a 20 degree range of adjustment relative to the crankshaft. From 2003, however, there were RN engines with dual CVVT (i.e. for intake and exhaust cams) such as the B5244T7 and B6294T. Subsequently, the B5244T4 and B5244T5 engines also had dual CVVT;
• Lower mass and internal friction: this was achieved through lighter crankshaft counterweights, lighter pistons, gudgeon pins and thinner valve stems that reduced reciprocating masses by 3.5-4.5 kilograms (depending on variant). Since the pistons were shorter, the length of the connecting rod was increased to 139.5 mm – this reduced piston-to-bore friction, improved combustion by holding the piston at TDC and BDC for longer duration and better ignition and cylinder fill, and increased torque;
• More free-flowing cylinder heads;
• Within the cylinder block, breather holes between the cylinders;
• An improved cooling system: for naturally aspirated engines, oil squirting jets beneath the pistons were introduced to improve cooling – for the N series, this had been limited to turbocharged engines). Piston cooling enabled:
  • Higher output without knock; and,
  • The top piston ring to be position 2 mm higher (at 5 mm from the top of the piston instead of 7 mm). As such, the pocket which formed between the piston, the piston ring and the cylinder wall was reduced, as was the amount of unburnt hydrocarbons that could collect in this area;
• All engines were fitted with external oil coolers; and,
• Electronic throttle control.

Furthermore, all RN engines had:

• Coil-on-plug ignition (not all N Series engines were so equipped); and,
• Four valves per cylinder (in the N Series, some engines had two valves per cylinder).

RN engine: mechanical (solid) valve lifters introduced in 1999

While RN series engines generally have mechanical valve lifters, engines produced up to mid-1999 had hydraulic lifters like the N Series engines. AustralianCar.Reviews understands that mechanical lifters commenced from engine number 1817653 and that, for these updated engines:

• The intake ports were approximately 20 per larger;
• The coolant and oil passages were modified;
• The base circle on the camshaft increased by 2 mm;
• Valve stem diameter decreased from 7 mm to 6 mm; and,
• Valve length and lift also changed.

The intake and exhaust valve diameters, however, were unchanged at 31 mm and 27 mm, respectively.

RN engine: mechanical (solid) valve lifters introduced in 1999

From 2002, RN engines were produced with 147 mm long connecting rods (previously 139.5 mm) and smaller gudgeon pins were introduced to reduce weight and friction. To accommodate this change,

• The compression height of the pistons was reduced;
• Piston skirt length was reduced; and,
• A lighter crankshaft was introduced to balance the change in reciprocating weight.

This design change increased the strength of the connecting rods and power output since the longer connecting rods stayed at top dead centre (TDC) for longer.

2004-07 Volvo S60 R and V70 R: B5254T4 engine

The Volvo S60 R and V70 R were powered by the B5254T4 engine. This engine differed from other contemporaneous RN series engines in that it had:

• Reinforced connecting rods that were 143 mm long;
• Reinforced pistons;
• Enhanced cylinder head cooling and airflow;
• A re-designed oil supply to ensure oil supply under extreme G-forces.

Like other post-2003 RN engines, the B5254T4 engine had variable intake and exhaust camshaft timing. The B5254T4 engine had a KKK K24 turbocharger that provided maximum charge pressure of about 1 bar and twin intercoolers.