Honda K24A8 Specifications
| Engine Model: Honda K24A8 |
| Engine Type: 4-cycle inline 4-cylinder DOHC 16-valve i-VTEC liquid-cooled gasoline |
| Total Displacement: 144 cu.in (2.35 L) |
| Rated Engine Power: 166 Hp (124 kW) at 5800 rpm |
| Fuel System Type: Multi-point electronic fuel injection |
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The Honda K24A8 is a 2.4-liter naturally aspirated
inline-four engine, serving as the final and most refined iteration of the
“economy” K24A series. Produced primarily for the North American market, it
represented the pinnacle of this specific lineage before the transition to the
subsequent K24Z family. Introduced in the mid-2000s, the K24A8 was engineered to
deliver a balance of respectable performance, enhanced fuel economy, and
stringent emissions compliance, achieving Partial Zero Emission Vehicle (PZEV)
status in certain applications.
Building upon the foundations of its K24A4 and K24A6 predecessors, the A8
variant incorporated a series of strategic internal and external refinements.
The primary focus was optimizing airflow and combustion efficiency. Key updates
included a higher-flow intake manifold, revised exhaust tuning with a larger
diameter pipe, and an updated engine control unit (ECU) calibration.
The engine retained Honda’s i-VTEC (intelligent Variable Valve Timing and Lift
Electronic Control) system but maintained the “economy” configuration, where the
system operates exclusively on the intake camshaft to promote low-speed swirl
for efficiency before switching to a high-lift profile for increased power. The
result was a marginally higher power output, smoother operation, and a
reputation for robust reliability and longevity, making it a well-regarded
powerplant in the final years of the seventh-generation Honda Accord.
The K24A8 is a water-cooled, four-stroke, spark-ignition engine.
Engine Type: Inline-4, naturally aspirated.
Displacement: 2,354 cc (144.0 cu.in).
Bore: 87.0 mm (3.43 in).
Stroke: 99.0 mm (3.90 in).
Compression Ratio: 9.7:1.
Valvetrain: DOHC (Double Overhead Camshaft), 16-valve, i-VTEC.
Firing Order: 1-3-4-2.
Maximum Power: 166 hp @ 5,800 rpm (124 kW)
Maximum Torque: 160 lb-ft @ 4,000 rpm (217 Nm)
Redline: 6,500 rpm
Engine Management: Honda PGM-FI (Programmed Fuel Injection) with Drive-by-Wire
throttle control.
Emissions Standard: Certified LEV2-PZEV (Partial Zero Emission Vehicle) in
applicable applications.
The engine’s power delivery is characterized by a broad torque curve, aided by
the early engagement of the VTEC system. The maximum figures represent a slight
increase over earlier K24A series engines due to improved volumetric efficiency.
VTEC Engagement Point: 2,400 rpm (intake camshaft switches from low-lift,
12-valve mode to high-lift, 16-valve mode).
The cylinder block is constructed from high-pressure
die-cast aluminum alloy to reduce overall engine weight, a critical factor in
vehicle dynamics and fuel efficiency. To ensure durability and a long service
life under various operating conditions, the aluminum block is fitted with
cast-iron cylinder liners. These liners provide a robust wear surface for the
pistons and piston rings.
The block is an open-deck design, meaning the cylinders are not fully supported
by the upper deck of the block. This design aids in cooling efficiency and
weight reduction. A structural aluminum oil pan is bolted to the lower
crankcase, adding to the engine’s overall rigidity and helping to dampen
vibration. The engine incorporates a dual counter-rotating balance shaft system,
housed within a module bolted to the lower crankcase and driven by the
crankshaft. This system is specifically designed to cancel out the secondary
vibrations inherent to a four-cylinder engine, resulting in a smoothness
characteristic of a larger-displacement six-cylinder engine.
The cylinder head is a lightweight aluminum alloy
casting, designed with a cross-flow pattern to optimize intake and exhaust
efficiency. It houses dual overhead camshafts, with the intake camshaft
featuring the i-VTEC mechanism. The valve arrangement consists of four valves
per cylinder - two intake and two exhaust - actuated by roller rocker arms that
reduce friction.
The i-VTEC system on the intake side uses three rocker arms per cylinder: a
primary rocker arm for one intake valve, a secondary rocker arm for the other
intake valve, and a middle rocker arm that is pinned to the primary and
secondary arms during high-lift operation. Below the VTEC engagement point
(2,400 rpm), the system operates in a 12-valve mode. In this mode, one intake
valve opens a minimal amount, while the other remains almost completely closed.
This creates a powerful swirl effect within the combustion chamber, promoting
leaner, more efficient combustion and reducing fuel consumption. Above the
engagement point, hydraulic pressure locks the rocker arms together, forcing
both intake valves to follow a higher-lift, longer-duration cam lobe for maximum
airflow and power.
Valve Material: Steel.
Valve Seat Inserts: Wear-resistant sintered alloy.
Valve Guides: Powder metal.
Camshaft Drive: Silent timing chain with automatic hydraulic tensioner.
The K24A8 utilizes Honda’s PGM-FI system, which is a
multi-point, sequential fuel injection setup. This system employs a fuel
injector for each cylinder, positioned to spray fuel directly onto the back of
the intake valves. Sequential injection means the ECU triggers each injector
individually in time with the engine’s firing order, allowing for precise fuel
metering under all operating conditions.
The system is fully integrated with the electronic throttle control
(Drive-by-Wire). This allows the ECU to manage idle speed, throttle progression,
and torque output seamlessly. The fuel system operates at a standard pressure
regulated by a returnless system, where the fuel pressure regulator is located
inside the fuel tank, reducing fuel heating and evaporative emissions. The
engine is calibrated to operate on regular-grade unleaded gasoline.
The lubrication system is a full-flow, pressure-fed
type, utilizing a high-efficiency trochoid pump. The oil pump is integrated with
the balance shaft assembly, located in the lower crankcase and driven by the
crankshaft via a chain. This integration provides a compact and efficient
design.
The system features a spin-on, full-flow oil filter with a built-in bypass valve
to ensure oil supply to the engine even if the filter becomes clogged. A piston
oil jet system is incorporated to spray oil onto the underside of the pistons.
These jets provide critical cooling to the piston crowns, particularly under
high-load conditions, improving durability and reducing the risk of detonation.
Recommended Oil Viscosity: SAE 5W-20.
Oil Capacity (with filter): 4.2 L (4.4 US qt).
Oil Pressure: Minimum 70 kPa (10 psi) at idle.
Oil Pressure: Nominal 350-490 kPa (51-71 psi) at 3,000 rpm.
The cooling system is a pressurized, thermosiphon-type
system using a cross-flow radiator to maintain optimal engine operating
temperatures. A belt-driven centrifugal water pump circulates coolant through
the engine block and cylinder head, where it absorbs heat before passing through
the radiator.
The system includes a wax-type thermostat with a bypass circuit to allow the
engine to reach operating temperature quickly. The thermostat begins to open at
approximately 78°C (172°F). A dual-speed electric cooling fan, controlled by the
ECU based on coolant temperature and A/C system pressure, ensures adequate
airflow across the radiator during low-speed operation or idle. The cylinder
head’s open-deck design and the aluminum construction of both block and head
contribute to rapid heat dissipation and uniform thermal management.
Coolant Capacity (engine only): 1.3 L (1.4 US qt).
Coolant Capacity (total system): 5.8 L (6.1 US qt).
Recommended Coolant: Honda Long-Life Antifreeze/Coolant Type 2.
| Intake and Exhaust Systems |
Intake System: The intake system features a
large-volume air cleaner housing and a high-flow intake manifold. The manifold
was updated for the K24A8 with longer, tuned runners to enhance low-end torque
while maintaining high-rpm flow. The Drive-by-Wire throttle body has no physical
cable connection to the accelerator pedal, allowing the ECU to modulate throttle
opening for functions such as idle control, traction control, and cruise
control.
Exhaust System: The exhaust manifold is a tubular stainless-steel design
optimized for flow. It is connected to an exhaust system with a larger diameter
pipe - 57 mm (2.24 in) compared to the 48 mm (1.89 in) used on earlier K24A
models - reducing backpressure and contributing to the engine’s modest power
increase.
The engine employs a direct ignition system with a
coil-on-plug setup. Each cylinder has its own ignition coil mounted directly
over the spark plug, eliminating the need for spark plug wires and providing a
powerful, precisely timed spark. This system allows the ECU to control ignition
timing with high accuracy for optimal performance and emissions control. Spark
Plugs: NGK IZFR6K-11 (Iridium, pre-gapped).
Overall Length: 610 mm (24.0 in)
Overall Width: 670 mm (26.4 in)
Overall Height: 670 mm (26.4 in)
Dry Weight (complete engine): 137 kg (302 lb)
Valve Clearance (cold
engine):
Intake: 0.21-0.25 mm (0.008-0.010 in).
Exhaust: 0.25-0.29 mm (0.010-0.011 in).
Spark Plug Replacement Interval: 160,000 km (100,000 miles). Timing Chain:
Inspect for noise and tensioner function. Engine Oil Change Interval:
8,000-10,000 km (5,000-6,000 miles) depending on driving conditions and oil
quality.
Coolant Replacement Interval: 160,000 km (100,000 miles) or 10 years, then every
80,000 km (50,000 miles) or 5 years thereafter. Drive Belt (Accessory): Inspect
for cracks and tension at regular intervals; replacement as needed.
Cylinder Head Bolts: 29 Nm (21 lb-ft); then 90° turn;
then 90° turn
Main Bearing Cap Bolts: 39 Nm (29 lb-ft) + 90° turn
Connecting Rod Cap Nuts: 24 Nm (18 lb-ft) + 90° turn
Camshaft Carrier Bolts: 24 Nm (18 lb-ft)
Camshaft Thrust Cover Bolts: 12 Nm (9 lb-ft)
Crankshaft Pulley Bolt: 181 Nm (133 lb-ft)
Flywheel/Flexplate Bolts: 98 Nm (72 lb-ft)
Intake Manifold Bolts: 24 Nm (18 lb-ft)
Exhaust Manifold Nuts: 27 Nm (20 lb-ft)
Spark Plugs: 18 Nm (13 lb-ft)
Oil Pan Bolts: 12 Nm (9 lb-ft)
Balance Shaft Assembly Bolts: 29 Nm (21 lb-ft) + 90° turn
Water Pump Bolts: 12 Nm (9 lb-ft)
The Honda K24A8 engine was utilized across several
models in the North American and select Asian markets during the mid-to-late
2000s. Its application was characterized by a focus on refined economy and
emissions compliance.
2006-2007 Honda Accord (North America): Fitted in the LX, SE (Special Edition),
and EX trims for both sedan and coupe body styles. This was the primary
application, where the engine replaced the earlier K24A4 and K24A6 variants.
2007-2008 Honda Element (North America): Served as the sole engine option across
all trims (LX, EX, SC) for the final two model years of the first-generation
Element.
2008-2014 Honda Odyssey (Japanese and Asian Markets): Installed in the RB3 and
RB4 chassis codes of the Odyssey Absolute and other high-end variants in markets
such as Japan, Singapore, and Hong Kong. In this application, the engine was
often tuned for slightly different power characteristics to suit the
multi-purpose vehicle (MPV) platform.
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