The Honda K23A1 is a 2.3-liter turbocharged inline-four gasoline engine produced by Honda Motor Co., Ltd.. It belongs to the K-series family and was developed specifically for use in the Honda RDX (first generation) as a high-torque, low-lag turbo engine — a unique approach within Honda’s mostly naturally aspirated lineup.
Released in 2006, the K23A1 was Honda’s first production turbocharged gasoline engine sold in North America. It powered the first-generation Acura RDX and represented a shift in Honda’s engineering philosophy — prioritizing low-end torque and everyday drivability over the high-revving nature typical of engines like the K20A or K24A.
Featuring a single scroll turbocharger and advanced i-VTEC system on both intake and exhaust cams, the K23A1 was designed for smooth torque delivery, minimal turbo lag, and high reliability. It’s part of Honda’s K-series family but differs significantly in compression, boost control, and head design compared to its naturally aspirated relatives.
| Manufacturer | Honda Motor Co., Ltd. |
| Engine family | Honda K-series |
| Configuration | Inline-4, DOHC 16-valve, turbocharged |
| Displacement | 2,347 cc (2.3 L) |
| Bore × stroke | 87.0 mm × 99.0 mm |
| Compression ratio | 8.8 : 1 |
| Valvetrain | i-VTEC (intake & exhaust cam phasing) |
| Induction | IHI RHF5-style turbocharger (8.7 psi stock boost) |
| Power output | 240 hp (179 kW) @ 6,000 rpm |
| Torque | 260 lb-ft (353 Nm) @ 4,500 rpm |
| Fuel system | Multi-point PGM-FI |
| Fuel type | Premium unleaded gasoline (91 AKI+) |
| Redline | 6,800 rpm |
| ECU | Honda/Acura PCM (OBD-II compliant, drive-by-wire) |
| Production years | 2006–2012 |
The K23A1 was conceived during the early 2000s as a response to growing demand for torque-rich crossover engines. Unlike traditional VTEC engines that relied on high RPM for performance, Honda aimed to produce a compact turbo unit delivering instant torque at low speeds for daily drivability and all-wheel-drive systems.
Honda engineers selected an IHI RHF5 turbocharger with electronically controlled wastegate and air-to-air intercooler, ensuring consistent boost while maintaining smooth throttle response. Combined with a low-compression forged bottom end and strong cylinder head design, the engine could handle sustained boost pressure while meeting stringent U.S. emissions regulations.
The K23A1 retains Honda’s die-cast aluminum block with cast-in iron sleeves, similar to the K24A, but features reinforced cylinder walls and upgraded pistons to withstand boost. The crankshaft and connecting rods are forged steel, and the engine uses an oil-squirter system for piston cooling.
The aluminum head employs a dual-VTC i-VTEC system, controlling both intake and exhaust cam phasing for improved turbo spool and emissions performance. Unlike high-revving K20A heads, the K23A1’s valve timing prioritizes torque and midrange efficiency over peak power.
An IHI RHF5 turbocharger delivers around 8.7 psi (0.6 bar) of boost. The wastegate is electronically controlled by the ECU, providing smooth power delivery. Intake air is cooled through a front-mounted intercooler. The turbocharger’s modest sizing ensures minimal lag and instant throttle response — ideal for an SUV application.
The engine features an upgraded oil pump and high-capacity radiator system. Oil jets under each piston maintain stable temperature, critical for reliability under sustained boost. Honda’s cooling architecture allows consistent performance in both high-load and stop-and-go driving conditions.
| Model | Chassis | Market | Years |
|---|---|---|---|
| Acura RDX (1st Gen) | TB1 | North America | 2006–2012 |
The K23A1 produces a broad torque curve, reaching 90% of its peak torque from just 2,000 rpm. Acceleration in the Acura RDX is strong, with minimal turbo lag and linear power delivery — a result of Honda’s precise boost management and i-VTEC calibration.
In stock form, the RDX achieves 0–100 km/h in approximately 7.5 seconds, with fuel economy around 11 L/100 km (21 mpg US combined). Despite its forced induction, the engine retains Honda’s trademark refinement and throttle response.
The K23A1 is considered highly reliable for a factory turbo engine. It was engineered conservatively — low boost, robust internals, and an advanced knock-control system — allowing long lifespan even under spirited driving. However, as the first turbocharged Honda engine sold in the U.S., it introduced maintenance requirements unfamiliar to traditional Honda owners.
With proper maintenance, engines regularly surpass 300,000 km (≈185,000 mi) without major repairs. Turbochargers typically last 200,000+ km under moderate use.
The K23A1 has strong tuning potential thanks to its forged internals and turbo foundation. Common modifications include ECU tuning, larger intercoolers, and exhaust upgrades. The factory turbo can safely handle 10–12 psi with proper fueling, yielding ~280–300 hp on stock internals.
Aftermarket tuning solutions like Hondata FlashPro or KTuner enable recalibration of boost, ignition, and fueling. Flash tunes often unlock 30–40 hp with improved throttle response.
Stock bottom ends handle up to 350–380 hp safely. Beyond that, forged pistons and rods are recommended. The engine’s design lends itself well to daily-driven, reliable performance builds.
Major issues with the K23A1 are rare. Typical wear items include:
Owners on Acurazine and Reddit praise the K23A1 for its reliability and torque, often calling it “the turbo Honda that feels OEM perfect.” Mechanics highlight the engine’s simplicity compared to modern direct-injection turbos and appreciate its tolerance for boost tuning without internal upgrades.
Despite its modest power output by today’s standards, enthusiasts respect the K23A1 as a durable and balanced turbo platform that laid the foundation for later engines like the L15B7 (Civic 1.5T) and K20C1 (Civic Type R).
Disclaimer: Performance and specifications may vary by region and production year. Always consult official Honda service literature for precise data.