As the new Si is based on Honda's Global Small Car platform (Civic, RSX, CR-V), it's no surprise that it helps itself to the corporate parts bin when it comes to the drivetrain. For some automakers, this usually results in a variety of quite mediocre cars. But Honda seems to have this platform thing knocked, because they keep building winners. In this sense, the Si is fortunate to have a 2.0L K20 purring under the hood. This i-VTEC gem combines smoothness, quietness, great torque delivery, decent fuel economy, and excellent emissions characteristics. You may be thinking that the drivetrain has been lifted wholesale from a base model RSX, but there are in fact differences in gear ratios and even the rated torque.

i-VTEC

The Si's i-VTEC system utilizes two roller arms per pair of intake valves. During low-rpm operation, intake air is drawn almost exclusively through the primary intake valve, which createsa strong swirl effect to maximize combustion (and therefore torque). At higher rpm, the secondary rocker arm engages the primary roller, opening both intake valves for the same lift and duration, substantially increasing airflow into the cylinder and boosting performance.

VTC (Variable Timing Control)
The i-VTEC system adds a new camshaft VTC (Variable Timing Control) system to VTEC for continuously variable camshaft phasing across the engine's entire power band. As engine rpm builds, a VTC actuator -- controlled by an engine control unit that monitors cam position, ignition timing, and throttle position -- advances or retards the intake cam throughout the 50-degree timing range, optimizing engine output and reducing emissions.

During typical operation, the intake camshaft timing is almost fully retarded at idle to help provide more stable idling while reducing exhaust emissions (NOx). As rpm increases, the intake camshaft is advanced, opening the intake valve sooner and providing additional valve overlap. This results in increased fuel economy (by reducing pumping losses) and a further reduction in exhaust emissions (by creating a large, internal exhaust gas recirculation effect).

Also, to generate additional power throughout the rev range, the intake camshaft is continuously varying the amount of advance or retard, instantly adjusting to provide additional power as required by the driver.

Cylinder Head/Valve Train
The Civic Si engine features an aluminum cylinder head and a double-overhead-cam, four-valve-per-cylinder valve train. A large combustion chamber "squish" area increases gas turbulence for faster flame propagation and excellent efficiency. The camshafts are operated by a silent-chain drive that helps provide smooth, refined performance while also being maintenance-free.

Engine Block/Crankshaft
The powerplant has a compact aluminum block with cast-in iron liners - a design known for its light weight, high rigidity and excellent durability. The block has a one-piece aluminum crankshaft carrier that has ferrous-carbon inserts in the bearing caps for additional strength.

Programmed Fuel Injection (PGM-FI)
The advanced PGM-FI system of the new Civic Si monitors such variables as throttle position, engine temperature, intake-manifold pressure, atmospheric pressure, exhaust-gas oxygen content, and intake-air temperature. Fuel delivery is controlled by four newly developed, multi-holed injectors mounted in the cast-aluminum intake manifold. The ECU also tracks the operation of the engine with position sensors on the crankshaft and both camshafts.

Exhaust System
The exhaust system on the Si is a stainless-steel, low heat-mass design. Emissions performance is improved thanks to the engine's design, which positions the exhaust manifold to the rear of the engine - which shortens the distance that the exhaust gases must travel to the catalytic converter, resulting in faster light-off and more complete conversion of the exhaust gases. The system also employs a new, high-density catalytic converter for improved light-off performance and reduced hydrocarbons and NOx.

The Si reduces NOx emissions by 25 percent compared to the previous (2000) model, and is designed to meet strict 2004 Low Emissions Vehicle II (LEV II) standards.

Noise, Vibration, and Harshness (NVH) Control
The Civic Si engine has been engineered for class-leading smoothness and refinement. To that end, the following NVH-reducing features are incorporated: balancer shaft (integrated with the oil pump); highly rigid, ferrous-carbon inserts in the main bearing caps (for added rigidity); a one-piece crankshaft carrier; and a silent chain cam drive.

A sophisticated engine mounting system plays a key role in limiting noise and vibration in the interior space. Four engine mounts (two liquid-filled) and reinforcements in the engine compartment help further reduce engine noise and vibrations. Centrally mounted at the front of the engine bay is a lightweight, extruded aluminum mount. At the rear of the engine bay is a second mount made from resin that is designed to shear off in an impact, limiting the rearward movement of the engine. The two liquid-filled mounts (one fitted to the transmission) are positioned for maximum absorption on the 2.0-liter's NVH characteristics.

110,000 Mile Tune-Up Intervals
The Civic Si's first scheduled tune-up is required at 110,000 miles (obviously, routine inspections and fluid changes are required during this period). Credit for this longevity goes to platinum-tipped spark plugs, a long-life timing chain, and careful engineering of the DOHC drivetrain - which reliably maintains proper valve tappet clearances until the 110,000 mile first tune-up (under normal conditions)

5-Speed Manual Transmission
The standard (and only) transmission offering for the Civic Si is a close ratio 5-speed manual designed to optimize the performance characteristics of the i-VTEC engine. It is equipped with a short-stroke shift linkage for superb shifting quickness and feel. By employing multiple large-capacity synchronizers (triple cones for 1st and 2nd; larger diameter single cones on 3rd-5th), the 5-speed offers an exceptionally light and positive shifting effort.

For enhanced sportiness and shifting ease, the shift lever is mounted "rally style" within easy reach of the driver on the Civic Si's center console.

Comparing the gearsets of the Civic Si to the base model RSX, you'll see that the gear ratios of the Civic Si are overall a bit shorter than the RSX. Numerically, the Si's ratios for 1st and 2nd are both taller (lower numerically), but with a shorter (higher numerically) final drive ratio, the effective gearing ends up being shorter. In 3rd through 5th, the ratios are the same, but the effective gearing for the Si is shorter by a little over 8%, thanks to its shorter final drive. In case you were wondering, the new Si has an open differential (and there is no option for an LSD).