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2008 Honda S2000 – Powertrain At-A-Glance

2008 Honda S2000The S2000 powertrain uses a front-engine/rear-wheel-drive layout. The longitudinally mounted engine is mated to a 6-speed, close-ratio manual transmission. A driveshaft carries the output of the transmission to a frame-mounted Torsen limited-slip differential. The differential drives the rear wheels via independent axle shafts. The 2.2-liter, aluminum-alloy, inline 4-cylinder S2000 engine (engine code F22C1) produces 237 hp @ 7800 rpm and 162 lb.-ft. of torque @ 6800 rpm. The aluminum alloy cylinder head has dual overhead camshafts, four valves per cylinder and VTEC (Honda’s variable valve-timing system) on both the intake and exhaust valves. Fuel induction is via Honda’s sequential, Multi-Point Programmed Fuel Injection (PGM-FI) and the ignition system is a high-voltage, computer-controlled direct type with individual spark coils for each cylinder. The engine’s exhaust emissions qualify the S2000 as a California Low-Emission Vehicle 2 (LEV-2) and EPA Tier 2, Bin 5 vehicle.

Powertrain Summary

2.2-Liter (2157 cc) VTEC Engine

  • 237 hp @ 7800 rpm
  • 162 lb-ft. of torque @ 6800 rpm
  • 8000 rpm redline / 8200 rpm rev limit
  • DOHC VTEC cylinder head
  • Sequential, PGM-FI
  • Direct-ignition system with platinum-tipped spark plugs
  • Meets California LEV-2 standard

6-Speed Manual Transmission

  • Longitudinally mounted 6-speed manual transmission
  • Short-throw, direct shift linkage
  • High-performance clutch
  • Torsen limited-slip rear differential

Compact High-output Engine Block

The S2000 engine block is a one-piece, open-deck aluminum-alloy die casting. Of special note are the block’s FRM (Fiber-Reinforced Metal) cylinder liners cast integral with the block. FRM is a composite material consisting of carbon fibers embedded in an aluminum oxide matrix (aluminum oxide is a ceramic material used for spark-plug insulators). As a cylinder lining, FRM offers several advantages over conventional ferrous-metal liners, including lower weight, faster heat transfer and a greater resistance to wear. Additionally, “dummy head honing,” a process where the engine block cylinders are honed with a “dummy” cylinder head tightened to the block, improves machining accuracy for stability of piston movement. Cylinder bore is 3.42 in. (87.0 mm) and the stroke is 3.57 in. (90.7 mm). This results in a slightly “over square” 1:1.04 bore-stroke ratio that facilitates good torque characteristics at lower rpm while delivering high-rpm performance.

Forged-aluminum Pistons

The high-revving nature of the S2000 engine necessitated the use of special high-strength, lightweight forged-aluminum pistons. The piston’s minimal skirt area contributes to friction reduction. The carburized connecting rods and crankshaft, also steel forgings, are heat-treated for added toughness.

DOHC Cylinder Head

The S2000 engine’s DOHC, 16-valve cylinder head is a highly compact design, and like the engine block, is an aluminum-alloy die casting. The combustion chambers are a pent-roof shape, with four valves for optimum high-rpm airflow. A narrow (51-degree) included angle between the intake and exhaust valves helps to concentrate air and fuel around the spark plug, resulting in more complete combustion and greater efficiency. The valve springs are a single-element, round-profile type whose high-rpm design borrows heavily from Honda’s racing-engine building experience.

Variable Valve Timing and Lift Electronic Control (VTEC)

The S2000 engine uses a performance version of Honda’s innovative variable valve-timing system on both the intake and exhaust valves. VTEC maximizes the S2000 engine’s volumetric efficiency – packing the maximum amount of air and fuel into the combustion chamber on each intake stroke and expelling the maximum amount of exhaust gases on the exhaust stroke. VTEC works by varying valve timing and lift to compensate for the time delay and out-of-phase arrival of the air-fuel charge at the intake valve. Ideally, the valves should remain open for a short duration at low engine speeds and for a longer duration at high engine speeds- and that is precisely how VTEC works. In the S2000 VTEC engine, each intake and exhaust valve uses two different cam-lobe profiles: one for low engine speeds and a second for high engine speeds. From idle to around 6000 rpm, the two intake and exhaust valve cam followers at each cylinder are actuated by low-rpm cam lobes. Their short duration and low lift ensures good cylinder-filling at low engine speeds. At around 6000 rpm (depending on throttle position), an electronic control unit commands a spool valve to open and send oil pressure to pins in the cam followers. Under pressure, the pins lock the two intake-valve followers and the two exhaust-valve followers to a third follower. Until this moment, this third follower has been independently following the contour of a separate high-lift, long-duration cam lobe. Now the valves are actuated by the third follower and more closely match the induction and exhaust timing required for optimum torque at high engine speeds.

Compact Camshaft Drive

The S2000 engine’s dual overhead camshafts feature a space-efficient cam-drive consisting of a crankshaft-driven, silent-chain primary drive and a geared-secondary drive. The chain, along with a chain guide and an automatic tensioner, is located in an enclosed gallery at the front of the engine block. The primary chain turns an idler gear at its upper end, which drives the second stage- the intake and exhaust camshaft gears. The camshaft gears are smaller in diameter than conventional toothed sprockets, which allow the camshafts to be placed closer together, further saving space. Geared drives are widely used in racing engines because of their dependability and greater timing accuracy at high rpm. Each camshaft gear is a split (scissors) type, consisting of two concentric, spring-loaded gears, set at a slight angle from each other.

When engaging the teeth of the idler gear, the spring-loaded split teeth of the cam gear take up any backlash, ensuring smooth and quiet operation.

Lightweight VTEC Cam Followers

Because of the high-rpm nature of the S2000 engine and the need to save space, Honda engineers devised a unique VTEC cam follower system. The central element in a DOHC VTEC system is a roller-type, coaxial VTEC cam follower. The adoption of a roller for the area in contact with the camshafts helps to further reduce friction. At the same time, a reduced inertial moment has been made possible by integrating the sliding pin used to operate the cam profile switch into the roller structure. A precise metal-injection molding process is used to obtain the higher degree of rocker-arm finish required by the roller-type, coaxial VTEC design. This allows the use of the high-performance, high-lift cam profile over an extended range of engine speeds, so engine response and power output remain high all the way to its 8000 rpm redline. The two overhead camshafts are hollow in order to supply oil to the valvetrain with lubrication. This eliminates the need for a separate oil line and nozzles, which helps to simplify the cylinder-head lubrication system.

Powdered-metal, Injection-molded, Sintered Steel-alloy Cam Followers

A powdered-metal injection-molding process is used make the S2000 engine’s VTEC cam followers. In this process, powdered steel alloy is mixed with a binder that allows it to be injected into a mold, in much the same way that plastic items are injection-molded. The part is then removed from the mold and the binder is removed by heating. The rocker arm is then sintered, which involves heating the metal to just under its melting point in a special furnace so that the steel particles weld together.

Ladder-type Main-Bearing Carrier

The S2000 engine’s large ladder-type, cast-aluminum stiffener, with cast-iron bearing inserts, runs the full length and width of the lower engine block and contributes considerably to engine rigidity.

Cast-aluminum Oil Pan

A cast-aluminum oil pan bolts to the bottom of the main-bearing carrier. The pan is finned to help dissipate heat, and the use of an aluminum casting instead of a steel stamping provides additional rigidity to the engine and transmission. In addition, cast-aluminum radiates less engine noise than a customary steel-stamped pan.

Externally-mounted Oil Pump

To help minimize engine length, Honda engineers placed the oil pump at the bottom of the engine block instead of its usual location at the front of the crankshaft. This placement provides engine compactness, and the pump scavenges oil more efficiently. Additionally, the oil pump’s low placement helps pressurize the lubrication system more quickly during engine startup.

The oil pump itself also is a compact design that uses a smaller, high-speed rotor and suction-pickup ports on both sides of the pump body. The new design supplies a greater volume of oil to the engine at all engine speeds. The oil pump is driven via a silent chain connected to the crankshaft.

Compact Engine Ancillary Drive

The system for the engine ancillaries, such as the alternator, air-conditioning compressor and water pump, can take up considerable space at the front of the engine. On the S2000, these components are located at the side of the engine block (a practice commonly used on racing engines) and designed with a compact drive system that uses both sides of a serpentine belt. An automatic tensioner is built into the drive system.

Direct-ignition System

Instead of a distributor, the S2000 engine uses a computer-controlled direct-ignition system with individual high-voltage coils located at each spark plug. The spark plugs have non-fouling platinum tips for long life. Timing data for the ignition system is supplied to the engine’s Electronic Control Module by a pair of camshaft position sensors- one located on each camshaft – and a toothed-wheel crank-angle sensor located on the crankshaft. The Electronic Control Module automatically adjusts engine spark timing and dwell based on throttle opening, engine rpm, knock-sensor data, etc.

Integrated Air-intake System

In order to meet the S2000 engine’s performance requirements, the intake system has to be capable of moving a large volume of air. To achieve this, the entire intake system is placed in the space in front of the engine (made possible by the engine’s extreme rearward location in the engine compartment). In this location the system can draw cool air directly from in front of the main-forward engine-compartment bulkhead. Since the system does not sit on top of the engine, it also allows for a lower hood height and better forward visibility. The intake system consists of a large, 5.5-liter expansion chamber, a low-resistance, conical axial-flow air filter and a main resonator (intake-noise attenuator). From the air cleaner, intake air flows in a short, direct path to four large-section, tuned intake runners. The runners, along with the cylinder-head intake ports, have been carefully angled to provide the shortest, straightest airflow path into each cylinder.

Multi-point Programmed Fuel Injection (PGM-FI)

The PGM-FI is a timed, sequential system with sensors for throttle position, coolant temperature, crankshaft angle, intake-manifold pressure, atmospheric pressure, intake-air temperature, vehicle speed and exhaust-gas oxygen content. Information from these sensors is fed to an Electronic Control Module, which then decides when to activate each injector. PGM-FI can alter fuel delivery to match the engine’s needs under varying environmental and engine-load conditions.

Low Emission Vehicle 2 (LEV-2) Technology

Honda engineers designed the S2000 engine to have a high power output and also to be a LEV-2 engine. To accomplish this goal, they installed a high-flow, metallic honeycomb catalyst and applied a Linear Air Fuel (LAF) ratio sensor and an improved fuel injector.

Metallic Honeycomb Catalyst

The S2000 exhaust system uses a thin-walled, low-heat radiating metal honeycomb catalytic converter in place of the more traditional ceramic unit. The catalyst’s low backpressure also contributes to better engine performance.

Low-restriction Exhaust System

The S2000’s engine features a low-restriction, high-efficiency exhaust system. The manifold uses large-diameter stainless-steel tubing, and is a 4-into-2-into-1 design that promotes efficient gas flow. A pre-chamber and two main silencers further reduce back pressure. The S2000 CR eliminates the U-pipe in the muffler for a sportier exhaust note.

6-Speed Manual Transmission Overview

All six speeds and reverse gear of the S2000 are on two parallel shafts. Both transmission shafts are coupled at the output end. The use of carbon synchronizers for second through sixth gears helps reduce shift effort. First gear uses uses a brass synchronizer, while reverse gear uses a single-cone brass synchronizer for smooth shifting and quiet operation.

Transmission Gear Ratios

Gear Ratio
1st 3.133
2nd 2.045
3rd 1.481
4th 1.161
5th 0.943
6th 0.763
Reverse 2.800
Secondary Gear Reduction 1.208
Final Drive 4.100

Direct Shift Linkage

The transmission shift linkage is mounted on the top of the transmission case, helping to eliminate play in the linkage and provide optimum feel when changing gears. Shift throws are short and direct. Shift detents and lateral-spring pressure are set so that the shift-lever neutral position lies on the 3rd-gear/4th-gear axis. The shift lever floats in a rubber mounting that absorbs vibration. Reverse-gear lockout is a mechanical type, which can be released by pushing the shift lever downward. The S2000 CR spherical shift knob effectively shortens the shift throws.

Separate Lubrication Pump

High-performance transmissions that are subject to high amounts of stress can benefit from a separate lubrication system, so the S2000 manual transmission has its own lubrication pump. The pump provides positive and reliable lubrication, regardless of G-loading, and helps to prolong gear and synchronizer life.

Heavy-duty, Pull-type Clutch

The S2000 employs a pull-type clutch mechanism and reinforced friction materials well suited to the high-rpm nature of the powertrain.

Low-vibration Propeller Shaft

The propeller shaft that takes power to the rear differential in the S2000 is a strong, one-piece design. To reduce noise and vibration from the shaft, Honda engineers specified sliding, constant-velocity joints at both ends, instead of the more common U-joints. Constant-velocity joints also transmit power more uniformly over a range of angles.

Torsen Limited-slip Differential

The Torsen limited-slip differential (clutchless type) used in the S2000 is specifically adapted for high power output and automatically distributes torque to both rear wheels simultaneously or variably as traction conditions permit.

One-piece, Highly Rigid Axle Shafts

Power is transmitted from the differential to the rear wheels via a set of rigid, one-piece axle shafts. The shafts’ increased level of rigidity improves the powertrain’s response to throttle input.

Source: Honda

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