1UZ-FE Lexus engine

Introduction

The 1UZ-FE was a 4.0-litre V8 petrol engine that was developed for the Lexus XF10 LS 400. Key features of the 1UZ-FE engine included its aluminium alloy construction, double overhead camshafts per cylinder bank and four valves per cylinder. The 1UZ-FE engine underwent upgrades in late 1994 and 1997 – these changes are described in detail in the sections below.

Like the related 2UZ-FE and 3UZ-FE, the 1UZ-FE was a member of the UZ engine family.
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1UZ-FE block

The 1UZ-FE had an aluminium alloy cylinder block with a 90 degree ‘V’ angle for the cylinder banks. The 1UZ-FE engine had 87.5 mm bores – with bore pitch of 105.5 mm – and an 82.5 mm stroke for a capacity of 3969 cc; the cylinder banks were offset by 21 mm. Within the cylinder bores, the 1UZ-FE engine had cast-iron cylinder liners.

The 1UZ-FE cylinder block had water passages for coolant circulation, aluminium engine mount brackets and liquid-filled compound engine mounts.

From late 1994, the 1UZ-FE engine had 31 mm diameter passages in the crankshaft bearing area to relieve back pressure at the bottom of the pistons that was generated by the reciprocal movement of the pistons.

In late 1997, Lexus claimed that the rigidity of the cylinder block was increased for quieter operation.

Crankshaft, connecting rods and pistons

The 1UZ-FE engine had a forged steel crankshaft with six bolt main bearing caps, five main journals, four connecting rod pins and eight balance weights. The crankshaft bearings were made of kelmet (an alloy consisting of mainly copper and lead), while plastic region tightening bolts were used for both the crankshaft bearing cap bolts and connecting rod cap bolts.

Whereas most V8 engines have six crankshaft counterweights, the 1UZ-FE and 3UZ-FE V8 engines had eight counterweights. With eight counterweights, each weight was offset 180 degrees from its journal and provided better balance, particularly at higher engine speeds since the centripetal forces generated by any imbalance increase exponentially in proportion to speed. Due to cost, eight counterweight crankshafts are most common in racing engines, and their use in the UZ engines reflected their design being based on a racing CART/IRL engine and planned use in GT500 vehicles. Other race-style design features for the UZ engines included six-bolt cross mains and over square dimensions (bore exceeding stroke).

The 1UZ-FE engine had sintered and forged steel connecting rods, with connecting rod pins and journals that were induction-hardened for reliability. Furthermore, a weight-adjusting boss was provided at the big end to reduce fluctuation of weight and balance the engine assembly

The hypereutectic pistons had steel struts to control thermal expansion and full-floating type pistons pins that were held in place with snap rings. The skirt of each piston was striation finished (finely grooved) for proper lubrication and to reduce frictional losses. Furthermore, the surfaces of the no.1 compression ring and the oil ring side rail were nitrified to prevent oil consumption and blow-by gas. Like the connecting rods, each piston had a weight-adjusting boss to minimise fluctuation of weight among pistons and balance the engine assembly

As part of the 1UZ-FE update in late 1994, a lighter crankshaft and lighter connecting rods were introduced. For the pistons,

• The piston skirt area was made more compact and lightweight;
• Piston shape was modified;
• Lower tension piston rings were introduced to reduce friction;
• Shorter and thinner piston pins were used; and,
• The oil return hole in the oil ring groove was changed to a slot-less type.

In late 1997, a lighter and more rigid crankshaft was introduced. Furthermore, the piston head adopted a taper squish shape for improved combustion efficiency, while the shape of the piston was revised and a resin coating was applied to the piston skirt to reduce friction.

Cylinder head

The 1UZ-FE engine had an aluminium cylinder head in which the intake and exhaust ports had a cross-flow configuration. The intake ports were on the inside and the exhaust ports on the outside of the left and right banks, respectively. To conserve mass, the cylinder head had plastic region tightening bolts.

The original 1UZ-FE engine had a carbon graphite head gasket. In late 1997, however, a steel laminate type cylinder head gasket was introduced for greater reliability and to reduce cylinder bore deformation; its cross-sectional shape was also changed.

In late 1994, the water jacket in the cylinder head was modified to improve cooling performance in the area surrounding the combustion chamber. In turn, this improved anti-knocking performance.

Belt and gear driven camshafts

The 1UZ-FE engine had double overhead camshafts per cylinder bank (sometimes referred to as ‘quad cam’). The camshafts were made from cast iron and each cam nose was chill treated. The intake camshafts were driven by a timing belt, while the exhaust camshafts were driven by gears on the intake camshaft. For the exhaust camshafts, the scissors gear mechanism used a sub-gear with the same number of teeth as the drive gear and was attached to the gear on the driven side. Through the reaction force of the scissors springs, these two gears acted to pinch the drive gear, reducing backlash to zero and eliminating gear noise. For the timing belt, an auto-tensioner – which consisted of a spring and oil damper – maintained proper tension at all times. The camshaft journals and camshaft driven gear were lubricated by oil supplied to an oil passage in the centre of the camshaft.

In late 1997, the scissors gear was relocated from the centre of the camshaft to the front of the camshaft.

Valves

The 1UZ-FE engine had four valves per cylinder (two intake and two exhaust) that were actuated by aluminium alloy valve lifters. The 1UZ-FE engine had a narrow included valve angle (i.e. the angle between the intake and exhaust valves) of 21 degrees and 33 minutes.

The original 1UZ-FE engine had steel outer shim type valve adjusters that were located on top of the valve lifters. Valve dimensions for the original 1UZ-FE engine were as follows:

• Intake valve diameter: 33.5 mm;
• Intake valve stem diameter: 6.0 mm;
• Exhaust valve diameter: 28.0 mm; and,
• Exhaust valve stem diameter: 6.0 mm.

In late 1994, lower tension valve springs were introduced.

In late 1997, the valve diameter of the intake and exhaust valves was increased to reduce intake and resistance; valve stem diameter was also reduced. As such, valve dimensions for the post-1997 1UZ-FE were:

• Intake valve diameter: 34.5 mm;
• Intake valve stem diameter: 5.5 mm;
• Exhaust valve diameter: 29.0 mm; and,
• Exhaust valve stem diameter: 5.5 mm.

Other valve changes for the post-1997 1UZ-FE engine included:

• Increased valve lift;
• The introduction of inner shim type valve lifters that were made from aluminium; and,
• For mass reduction, the cross-sectional shape of the valve spring was changed from an egg-shape to a round shape with a smaller diameter.

Valve timing: non-VVTi

The original 1UZ-FE engine did not have variable valve timing and its valve timing is given in the table below. As such, valve overlap was 6 degrees, intake duration was 224 degrees and exhaust duration was 229 degrees.
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[/su_table]In late 1994, valve timing and valve lift for the intake valves were modified (see table below). As a result of these changes, valve overlap increased to 9 degrees, intake duration to 232 degrees and exhaust duration to 229 degrees.
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Valve timing: VVT-i

From late 1997, the 1UZ-FE engine was fitted with ‘Variable Valve Timing – intelligent’ (VVT-i) which controlled the intake camshaft within a range of 50 degrees of crankshaft angle to provide optimal inlet valve timing. As such, intake valve overlap ranged from -11 to 39 degrees, intake duration was 230 degrees and exhaust duration was 229 degrees.
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[/su_table]The VVT-i controller consisted of:

• An outer gear that was driven by the timing belt;
• An inner gear that was affixed to the camshaft; and,
• A movable piston that was placed between the outer gear and inner gear.

The movable piston had helical splines (twisted, vertical grooves) on its inner and outer periphery; as the piston moved in the axial direction to shift the phase of the outer gear and inner gear, valve timing was adjusted. The camshaft timing oil control valve controlled the position of the spool valve in accordance with signals from the ECM and applied hydraulic pressure to the intake camshaft timing pulley (to the advance or retard side).

Intake and throttle

The intake for the 1UZ-FE engine featured a dual mode type resonator chamber that was separated by a partition and used to reduce intake air noise.

The original 1UZ-FE engine had EGR (Exhaust Gas Recirculation) and ISC (Idle Speed Control) passages within the intake air chamber. Of these,

• The EGR system recirculated a portion of the exhaust gas back into the intake air-fuel mixture to slow down combustion in the cylinder and lower the combustion temperature – this, in turn, reduced the amount of NOx emissions. In late 1994, an EGR cooler was introduced to improve anti-knocking performance; and,
• The ISC valve was on the intake air chamber and intake air bypassing the throttle valve was directed to the ISC valve through a hose

The EGR cooler was enclosed in the rear water bypass joint (at the back of the engine) and used the engine coolant to cool exhaust gases that were subsequently drawn into the intake chamber. The EGR cooler limited the increase in intake air temperature from the exhaust gases and improved anti-knocking performance. As part of the late 1997 update for the 1UZ-FE engine, exhaust gas recirculation was omitted.

The throttle body contained the throttle valve that regulated the amount of intake air. The throttle position sensor detected the throttle valve opening and the dash pot that reduced the closing speed of the throttle valve.

In late 1997, the ‘Electronic Throttle Control System – intelligent’ (ETCS-i) was introduced such that the throttle valve opening was controlled electronically according to accelerator pedal effort and engine conditions. ETCS-i controlled the Idle Speed Control (ISC) system, cruise control and Vehicle Skid Control (VSC)

For the intake manifold, the ports were crossed to increase port length and the inertia effects of the intake air. In late 1997, a long port intake manifold was introduced to improve torque at low to mid engine speeds, and an upright intake port was adopted to improve intake efficiency.

From late 1997, the 1UZ-FE engine was fitted with an ‘Acoustic Control Induction System’ (ACIS). ACIS used a bulkhead to divide the intake manifold into two stages with an intake air control valve in the bulkhead that varied the effective length of the intake manifold according to engine speed and throttle valve opening to utilise the effect of inlet pulsations.

In late 1997, a heat-barrier gasket was introduced between the cylinder head and the intake manifold to limit heat transfer – this reduced intake air temperature and improved charging efficiency.

Injection and ignition

The original 1UZ-FE engine had multi-port fuel injection (MFI) which used a 4-group type injection pattern and injected into two cylinders each via two-hole injectors (four-hole injectors were introduced in late 1997). When a solenoid coil received a signal from the ECU, the plunger was pulled against spring force. Since the valve needle and plunger were a single unit, the valve needle was also pulled from its seat and fuel was injected. Fuel volume was controlled by the duration of the signal.

In late 1994, the 1UZ-FE adopted sequential multiport fuel injection (SFI). With SFI, the air-fuel mixture was introduced into each cylinder every time the engine completed two revolutions and injection timing was regulated according to engine condition.

The original 1UZ-FE engine had a cold start injector that injected fuel into the intake air chamber during engine cranking. In starting the engine when the engine coolant temperature was 22 degrees Celsius or lower, the cold start injector’s operation time was controlled by the start injector time switch. When starting the engine when engine coolant temperature was 60 degrees or lower, the operation time of the cold start injector was controlled by the ECU. The cold start injector, however, was discontinued in late 1992.

The original 1UZ-FE engine had an optical Karman-Vortex type air flow meter that was positioned between the air cleaner and the throttle body. The Karman-Vortex air flow meter measured the intake air volume electrically: as air flowed past the vortex generator, vortices were generated at a frequency proportional to the velocity of the air flow. The vortices were detected by subjecting the surface of a thin metal foil (mirror) to the pressure of the vortices and optically detecting the vibrations in the mirror by means of a luminous diode and a photo transistor. A calculation of the frequency could then determine the amount of air flow.

In late 1994, the Karman-Vortex type air flow meter was replaced by a hot-wire type mass air flow meter for improved accuracy in measuring intake air volume. In late 1997, the hot wire mass air flow meter was changed to a plug-in type.

The 1UZ-FE engine had pentroof type combustion chambers in which squish areas guided the air-fuel mixture to the centre of the combustion chamber to increase combustion speed. In late 1997, taper squish combustion chambers were adopted to improve anti-knocking performance and intake efficiency. The 1UZ-FE engine had twin knock sensors and the firing order was 1-8-4-3-6-5-7-2.

The original 1UZ-FE engine had a compression ratio of 10.0:1. From late 1994, the compression ratio was 10.4:1; from late 1997, the compression ratio was 10.5:1.

Exhaust

For the 1UZ-FE engine, both exhaust manifolds were made of stainless steel and covered with heat insulators to protect surrounding parts from exhaust heat. The catalytic converters (start and main) were monolithic type three-way catalytic converters.

The stainless steel exhaust pipe consisted of three sections: front, centre and tail. The centre section consisted of a single pipe, while the front and tail sections had dual pipes to reduce exhaust resistance.

In late 1994, the exhaust manifold was changed from the single type to the semi-dual type to reduce exhaust gas interference during low- and mid-range, and to reduce back pressure during high-speed operation. Furthermore, the method for joining the exhaust pipes together was changed from the flange type to the clamp type.