Dynamic Force Series — Toyota
A25A-FKS 2.5L
Inline-4 naturally aspirated gasoline engine. Toyota’s founding Dynamic Force design, in production since 2017.
- Displacement
- 2,487 cc
- Power
- 203–206 hp
- Torque
- 184 lb-ft
- Compression
- 13.0:1
Overview
The A25A-FKS is a 2.5-liter inline-four gasoline engine and the founding member of Toyota’s Dynamic Force family — the design that replaced the older 2AR-FE and set the template for Toyota’s current naturally aspirated four-cylinder lineup.
Toyota reached roughly 40% thermal efficiency with this engine, among the best figures achieved with a conventional gasoline design, through a long-stroke layout, dual injection, and a high 13.0:1 compression ratio.
Vehicles That Use This Engine
- Toyota Camry XV70, 2018–present
- Toyota RAV4 XA50, 2018–present
- Toyota Highlander XU70, 2019–present
- Toyota Avalon XX50, 2018–present
- Toyota Venza / Harrier XU80, 2020–present
- Lexus ES250 A25A-FXS hybrid
Crankshaft
Converts the up-and-down motion of the pistons into rotational force sent to the transmission. Supported by five main bearings, with balance shafts fitted to cancel out secondary vibration from the long-stroke design.
Why forged steel: the A25A-FKS’s long 103.4mm stroke puts more torsional stress on the crankshaft than a shorter-stroke engine. Forging aligns the steel’s grain structure for higher fatigue resistance than a cast crank, which matters more here than in a shorter-stroke design.
Pistons
Slide inside the cylinder bores, transferring the force of combustion to the connecting rods. Toyota uses a T-shaped design with a resin coating on the skirt and DLC (diamond-like carbon) coating on the rings.
Why aluminum: aluminum’s low weight reduces reciprocating mass, letting the engine rev more freely and reducing strain on the crankshaft and rods. Oil jets cool each piston from below to offset aluminum’s lower heat tolerance versus steel.
Cylinder Block
The structural core of the engine — houses the cylinders, crankshaft, and coolant passages. Uses an open-deck design with cylinder sleeves cast directly into the block.
Why this combo: aluminum keeps the block light, while thin cast-iron liners give the cylinder walls the wear resistance aluminum alone can’t provide. The tradeoff: less material for a rebuild compared to older cast-iron blocks.
Connecting Rods
Link each piston to the crankshaft, transferring the force of combustion into rotational motion. Described by Toyota as “high-strength” rods, built lightweight to keep reciprocating mass down.
Why forged steel: connecting rods take repeated tension and compression loads thousands of times per minute. Forging gives the steel a continuous grain flow along the rod’s shape, which resists fatigue cracking far better than a cast or machined-from-billet alternative at this weight.
Cylinder Head
Sits atop the block and houses the valves, camshafts, and combustion chambers. The A25A-FKS uses a 16-valve aluminum head with two chain-driven camshafts mounted in a separate casing on top.
Why aluminum: the head dissipates heat faster than iron would, which matters for an engine running a high 13.0:1 compression ratio. The tradeoff, noted by independent engine reviewers, is that the laser-clad intake valve seats and cast-in sleeves leave little material margin for a head rebuild compared to older cast-iron designs.
Timing Chain
Keeps the crankshaft and both camshafts synchronized. The A25A-FKS uses a single-row, low-friction roller chain with an 8.0mm pitch and a hydraulic tensioner — no belt, and no scheduled replacement interval under normal maintenance.
Why steel: unlike a rubber timing belt, a steel chain runs submerged in engine oil and is built to last the life of the engine. Toyota’s own service guidance calls for inspection around 200,000 km (125,000 miles), not replacement, under normal conditions.
Intake Manifold
Routes filtered air from the throttle body to each cylinder. Toyota uses a fixed-geometry plastic manifold on the A25A-FKS, paired with an electronically controlled throttle body (ETCS-i).
Why plastic: composite intake manifolds are significantly lighter than cast aluminum, and intake air temperatures are low enough that plastic’s heat tolerance isn’t a limiting factor here. The weight savings and lower manufacturing cost outweigh any durability edge aluminum would offer at this location.
Exhaust Manifold
Collects exhaust gas from all four cylinders into a single path. On the A25A-FKS, the exhaust manifold (header) is stainless steel with an integrated catalytic converter and EGR pipe built in.
Why stainless steel: exhaust gas exiting the cylinders runs far hotter than intake air, and stainless steel resists the heat cycling and oxidation that would corrode ordinary steel over time. Integrating the catalyst directly into the manifold also gets it hot faster on cold starts, cutting emissions sooner.
Spark Plugs
Ignite the compressed air-fuel mixture in each cylinder. The A25A-FKS uses coil-on-plug ignition with iridium-tipped spark plugs (Denso FK20HR11 or equivalent, OEM part 90919-01289), gapped at 1.0mm, with a long 120,000-mile replacement interval.
Why iridium: iridium is harder and has a higher melting point than the platinum or nickel used in older plug designs, letting Toyota use a finer electrode tip that ignites more precisely while lasting roughly 2-4x longer than a standard nickel plug before replacement is needed.
Piston Rings
Seal the gap between the piston and cylinder wall, keeping combustion pressure in the chamber and oil out of it. The A25A-FKS uses DLC (diamond-like carbon) coated compression rings and oil rings, a step up from the plasma-moly or chrome coatings used industry-wide on this ring type.
Why moly/DLC coating on a steel base: the ring body needs steel’s strength and heat tolerance to survive direct contact with combustion, but the coating is what actually touches the cylinder wall thousands of times per minute — DLC and moly coatings cut friction and wear far more than bare steel could on its own.
Valve Cover
Caps the top of the cylinder head, sealing in the camshafts and valvetrain while keeping oil contained. Toyota specifies a polymer (plastic composite) head cover on the A25A-FKS, torqued to just 9 Nm — noticeably lighter spec than the metal bolts elsewhere in the engine.
Why polymer: the valve cover carries no structural or combustion load — its only jobs are sealing and covering — so plastic’s weight savings come with essentially no downside. It also resists the minor corrosion that a stamped steel cover would eventually show from oil and condensation exposure.
Head Gasket
Seals the joint between the cylinder block and cylinder head, containing combustion pressure, coolant, and oil in their separate passages. Toyota’s Dynamic Force family uses a multi-layer steel (MLS) gasket design — several thin steel layers rather than a single composite sheet.
Why multi-layer steel: MLS gaskets conform to microscopic surface irregularities in the aluminum head and block better than a single-layer gasket, and steel tolerates the repeated heat-cycling of this engine’s 13.0:1 compression ratio far longer than older composite or copper gasket designs.
Intake & Exhaust Valves Industry-standard for this valve type
Open and close to let air/fuel in and exhaust out, sealing tightly against the valve seat under every combustion cycle. The A25A-FKS runs 35.8mm intake and 29.0mm exhaust valves at a 41-degree included angle, actuated via roller rocker arms with hydraulic lash adjusters.
Why chromium steel: intake valves typically use a chromium-silicon alloy (often called “Silchrome”), while exhaust valves — which run far hotter — commonly use a higher-chromium martensitic or austenitic stainless steel, sometimes with a nickel addition for extra heat resistance. Toyota’s exact alloy grade for this specific engine isn’t published, so this reflects the standard construction for valves of this type rather than a confirmed Toyota spec.
Valve Springs Industry-standard for this part type
Close each valve after the camshaft lobe releases it, keeping the valve seated against the head until the next opening cycle. The A25A-FKS uses hydraulic tappets to maintain continuous zero valve clearance alongside these springs.
Why chromium-silicon steel: valve springs cycle thousands of times per minute at redline and need to resist fatigue failure over hundreds of thousands of cycles without losing tension. Chromium-silicon spring steel is the industry-standard choice for this reason across nearly all modern gasoline engines.
Camshafts Industry-standard for this part type
Convert rotational motion into the precise up-down timing that opens and closes each valve. The A25A-FKS runs dual overhead camshafts with VVT-iE electric control on the intake side, driven by the single-row timing chain.
Why chilled cast iron: camshafts need lobe surfaces hard enough to resist wear from constant contact with the rocker arms, while the shaft itself stays cost-effective to cast at this shape. Chilled casting hardens just the surface layer, which is the industry-standard approach for this part.
Fuel Injectors
Meter and spray fuel into the cylinder. The A25A-FKS uses Toyota’s D-4S dual system: six-hole direct injectors delivering up to 20 MPa into the combustion chamber, plus 10-point port injectors on a steel-stamped low-pressure fuel rail.
Why stainless steel: injector nozzles and internals need to resist corrosion from constantly-flowing fuel and, on the direct injectors, extreme heat right at the edge of the combustion chamber — stainless steel handles both without degrading the precision of the spray pattern over time.
Throttle Body Industry-standard for this part type
Controls airflow into the intake manifold based on accelerator input. The A25A-FKS uses Toyota’s electronically controlled ETCS-i throttle body — no mechanical cable linkage to the pedal.
Why aluminum: the throttle body needs a stable bore that won’t warp with heat cycling, since even small dimensional changes would affect airflow precision. Aluminum holds tolerance well at low weight, which is why it’s the standard choice industry-wide for this part.
Oil Pan Industry-standard for this part type
Bolts to the bottom of the block and holds the engine’s oil supply, with the oil pump drawing from it. Toyota’s Dynamic Force engines generally use an aluminum pan, which also adds structural rigidity to the bottom of the block.
Why aluminum: beyond weight savings over stamped steel, an aluminum pan dissipates heat from the oil faster, and its added rigidity helps damp engine noise and vibration versus a thin steel stamping.
Oil Pump
Circulates pressurized oil to every moving part in the engine. The A25A-FKS uses Toyota’s second-generation variable-pressure oil pump, electronically controlled by the ECM to match oil pressure to actual engine load rather than running at a fixed rate.
Why this combo: the housing is aluminum for weight and heat dissipation, while the internal gears (gerotor or vane-type) are steel because they need to resist wear from constant meshing under pressure — a soft aluminum gear would wear out quickly.
Water Pump
Circulates coolant through the block, head, and radiator. The A25A-FKS uses an electric motor-driven water pump rather than a belt-driven one, letting the ECM run coolant flow independently of engine RPM for faster warm-up.
Why aluminum and composite: going electric let Toyota move away from the traditional cast-iron pump housing bolted directly to the block; the electric unit’s housing is typically aluminum with a composite impeller, since the impeller no longer needs to survive being belt-driven at engine speed.
Thermostat Industry-standard for this part type
Regulates coolant flow to the radiator based on engine temperature, keeping the engine at its optimal operating range. The A25A-FKS uses an electronically controlled thermostat as part of its broader variable-flow cooling system.
Why composite: electronically controlled thermostats typically use a composite housing around a wax-pellet actuator, which expands predictably with heat to open the valve — composite resists the corrosion a metal housing would face from long-term coolant exposure.
Radiator Industry-standard for this part type
Sheds engine heat from the coolant before it recirculates back through the block and head. Standard modern construction pairs an aluminum core with plastic end tanks.
Why this combo: aluminum’s thermal conductivity is what actually sheds the heat, while plastic end tanks are lighter and cheaper to mold into complex shapes than the brass tanks older radiators used — a tradeoff that shows up as the plastic tanks being the more common failure point over a vehicle’s life.
Alternator Industry-standard for this part type
Generates electricity to recharge the battery and power the vehicle’s electronics while the engine runs. The Euro 6 A25A-FKS uses an enhanced alternator paired with battery monitoring for idle stop/start energy management.
Why this combo: the aluminum housing sheds heat from the internal windings efficiently at low weight, while copper is used for the windings themselves because of its excellent electrical conductivity — there’s no practical substitute for copper in this role.
Starter Motor Industry-standard for this part type
Cranks the engine over to initiate combustion. Toyota’s closely related M15 Dynamic Force engine specifies a 1.0 kW starter for standard models and a 1.2 kW unit with integrated relay for models with idle stop/start.
Why this combo: a steel housing contains and directs the magnetic field the motor relies on, while copper windings again handle current flow — the same fundamental tradeoff as the alternator, just optimized for a short burst of high torque rather than continuous generation.
Drive Belt Industry-standard for this part type
Drives the alternator and other accessories off the crankshaft pulley. Because the A25A-FKS uses an electric water pump rather than a belt-driven one, this serpentine belt has fewer accessories to power than on older engine designs.
Why EPDM rubber: EPDM (ethylene propylene diene monomer) is the industry-standard material for accessory belts because it resists the heat, oil exposure, and ozone degradation found in an engine bay far better than older neoprene rubber compounds did.
Drive Pulleys Industry-standard for this part type
Guide the serpentine belt around the accessory drive system. Most are simple steel pulleys, though some idler and tensioner pulleys use a composite outer wheel to reduce belt noise.
Why steel: pulleys need to hold a precise, stable diameter under constant belt tension and vibration for the belt to track correctly — steel’s dimensional stability makes it the standard choice, especially for the crankshaft and alternator pulleys carrying the most load.
Flywheel
Bolts to the rear of the crankshaft, smoothing out power delivery between combustion pulses and providing the mounting surface for the clutch or torque converter. Toyota specifies 85 Nm for the flywheel bolts on the A25A-FKS.
Why steel: the flywheel’s entire job depends on rotational mass, which steel provides efficiently and at low cost — the added weight is the point, not a tradeoff, since it’s what smooths out the engine’s power pulses.