Holden LN3 ‘3800’ V6 engine (1989-90)

Introduction

The LN3 was a 3.8-litre pushrod V6 petrol engine that was first used in Australia in the VN Commodore. Developed by General Motors, the LN3 engine was also known as the Buick-Oldsmobile-Cadillac (BOC) V6 and had 90-degree V’ cylinder banks, 96.5 mm bores and an 86.3 mm stroke for a capacity of 3791 cc. The LN3 engine was initially assembled in Australia from components that were exported from Canada.

Although the LN3 engine had its origins in a GM engine that was in 1962, the BOC V6 was completely redesigned for 1988 and was the fifth generation of V6 engines produced by GM. As part of the redesign, the new cylinder block was redesigned with 23 per cent less reciprocating mass and a balance shaft was introduced.

LN3 block

The LN3 block was made from cast iron and, despite its greater capacity, weighed 5kg less than the 3.0-litre RB30 engine of its VL predecessor. Unlike other GM vehicles, the LN3 engine was mounted longitudinally and at a three degree incline for its use in Holdens. At the time, Holden’s VN version was the world’s only rear-wheel drive application of the BOC V6; Chevrolet followed later with its Camaro and Firebird.

LN3 internals

The LN3 engine had an offset crankshaft that was supported by four main bearings and counterbalanced by the flywheel/torque converter, crankshaft balancer and weights that were cast into the crankshaft itself.

The camshaft was supported in the crankcase by four bearings and driven from the crankshaft by sprockets and chain. To reduce inertial forces, the LN3 also had a balance shaft within the block that was positioned above and parallel to the camshaft and driven by the camshaft gearing.

Furthermore, the aluminium alloy pistons had full skirts, were tin-plated and cam-ground.

LN3 cylinder head

The LN3 had a cast-iron, cross-flow cylinder head with integral valve stem guides. For use in Holden vehicles, the one-piece aluminium intake manifold was locally-designed to allow for the Manifold Absolute Pressure (MAP) sensor of the Delco management unit (described further, below). The intake manifold was bolted to the inner faces of both cylinder heads to connect with the inlet ports.

LN3 valves

The LN3 engine had pushrod-operated overhead valves (OHV) with two valves per cylinder. The tubular pushrods operated overhead rocker arms which pivoted on pedestals that were bolted to the cylinder head. In addition to the normal function as a cam-follower, each hydraulic valve lifter served as an automatic adjuster so that manual valve adjustment was not required. Furthermore, the hydraulic valve lifters maintained zero lash in the valve train under all operating conditions.

Each exhaust and inlet valve had a double valve spring for positive valve seating throughout the rpm range (though single valve springs were subsequently introduced, see October 1989 LN3 upgrades’, below).

LN3 injection and ignition

The LN3 engine had electronic, multi-point port fuel injection which used a Bosch fuel rail and Bosch director plate-style injectors. Designed for 91 RON unleaded petrol, the fuel system was controlled by a Delco GMP4 electronic speed-density engine management system. Furthermore, the LN3, L27 and L36 engines all had MEMCAL (Memory Calibration) chips were detachable from the main ECU and contained calibrations for specific vehicle/engine combinations such as spark timing, fuel control and idle speed. For each model, it was not uncommon for a number of different MEMCAL settings to have been developed.

The computer-controlled coil ignition system had three ignition coils that were packaged in a single unit and only one coil was fired at any one time. Each coil fired two spark plugs simultaneously, but the plugs allocated to each coil were grouped so that when one plug was fired on the compression stroke, the other plug would fire on the exhaust stroke. Furthermore, dual electro-magnetic Hall-effect sensors were mounted at the front of the engine (behind the harmonic balancer) for ignition timing.

The LN3 engine operated at a compression ratio of 8.5:1.

LN3 exhaust

For the LN3’s use in Holden models, Holden developed new exhaust manifolds (and throttle controls) due to the position of the rack-and-pinion steering system. Australian-manufactured catalytic converters were also located in the exhaust pipe for emissions compliance.

LN3 performance

Upon its release in the VN Commodore, the LN3 engine produced peak power and torque of 125kW at 4800 rpm and 292Nm at 3600 rpm. Impressively, however, 92 per cent of peak torque (i.e. 268.6 Nm) was available from 1200 rpm. Due to its significantly higher outputs than the RB30 engine which it replaced, the LN3 engine had an axle ratio of 3.08:1 compared to 3.45:1 for the RB30.

Maximum engine speed for the LN3 was 5500 rpm.

LN3 transmissions

The LN3 engine was offered with Borg Warner T5 five-speed manual and GM Turbohydramatic (THM) 700 four-speed automatic transmissions. For its use in Holden vehicles, a new flywheel was developed for vehicles with manual transmission.

October 1989 LN3 upgrades

In October 1989, the following upgrades were introduced for the LN3 engine:

• Introduction of moulded plastic rocker covers with revised seals and retainers;
• Single valve springs (previously double valve springs);
• The steel pushrod guide plate was replaced by three alloy retainers with revised rocker arm pivots;
• For the camshaft, changes included decreased lobe lift, increased valve timing duration and installation of a thrust washer;
• For models with automatic transmissions, a retaining plate was fitted to the drive plate;
• The gasket between the pick-up pipe and the cylinder block was replaced by an O’ ring and the direction arrow on top of the pistons was omitted;
• For the cooling system, a reserve coolant tank was installed, while an overflow hose and cap were fitted to the surge tank; and,
• During 1990, high flow hydraulic tappets were introduced – these were identifiable by a yellow snap ring above the pushrod seat.