2004 Acura TSX -- Powertrain - Part 2

The i-VTEC 4-cylinder engine features Programmed Fuel Injection (PGM-FI), which relies on an array of sensors to constantly monitor a number of critical operating variables. The system tracks throttle position, intake air temperature, water temperature, ambient air pressure (altitude), intake manifold pressure, exhaust/air/fuel ratios and the position of the crankshaft and camshaft. High-efficiency air-assisted fuel injectors deliver fuel to each cylinder. These multi-hole injectors direct fuel around the intake valve stem for improved atomization, better power output and reduced emissions.

The TSX uses a single-stage intake manifold that is specially tuned for the engine's power characteristics. Fixed-length intake runners are tuned in length, size and shape to provide an optimal blend of low-rpm torque and high-rpm response, while supporting the advanced i-VTEC valve control system.

Exhaust flow is critical to performance and figures heavily in the strong power characteristics of the TSX. The high-flow rear-mounted exhaust manifold is constructed of stainless steel. Downstream, large pipe sizes increase flow, and the system splits to feed into free-flowing dual silencers and exhaust tips.

As automotive emissions standards tighten, a trend toward decreased power output is the natural result. The challenge with the new TSX was to advance power output while simultaneously reducing emissions. The payoff for these efforts was a strong 83 horsepower per-liter peak output, coupled with compliance with some of the toughest emissions regulations in America, the California Air Resources Board (CARB) LEV-2 standard. Compared to LEV-1-LEV, this stricter standard mandates a 75-percent reduction in NOx level and extends the emissions compliance/useful life by 20 percent, to 120,000 miles.


Tier 2-Bin 5

50,000 mi.

100,000 mi.

50,000 mi.

120,000 mi.

CO (g/m)





NMOG (g/m)





NOx (g/m)





*NMOG = Non Methane Organic Gas

The foundation for exceptional emissions performance was laid by the basic architecture of the TSX. The exhaust port and exhaust system are positioned to the rear of the transversely mounted engine. This means the catalytic converter can be positioned closer to the engine than is possible with a conventional front-exhaust configuration that sweeps under the engine to reach the converter. With the under-floor catalyst, light-off of the multi-cell converter is quick after starting. A low heat-mass stainless steel exhaust manifold also speeds converter light-off.

The i-VTEC cylinder head plays a large role in emissions reduction as well, by fostering internal exhaust gas recirculation, which cuts NOx. Air-assisted fuel injectors reduce hydrocarbons after starting, while a Linear Air/Fuel sensor positioned in the exhaust system just upstream of the catalyst improves air/fuel mixture control.

The cylinder head is pressure-cast aluminum alloy and features four-valves-per-cylinder driven by dual overhead cams. An automatically adjusted silent-type chain drives the cams; it is maintenance free and runs in an oil bath for maximum durability. The combustion chambers have large "squish" areas to promote faster flame propagation and more complete burning-factors in reduced carbon monoxide (CO) and hydrocarbon (HC) exhaust emissions.

The TSX uses a forged-steel crankshaft with a relatively long 99 mm throw. To reduce friction and improve long term durability, the crankshaft journals are micropolished. The die-cast lightweight aluminum block has cast-in iron cylinder liners with 87 mm bores. The liners are made using a spin casting, centrifugal process. To maximize the rigidity and minimize noise and vibration, the block is a 2-piece design that fully supports the five main bearings with a single cast-alloy bed-plate assembly.

The high output in-line 4-cylinder engine features comprehensive NVH reduction features. The pressure-cast block with its bed-plate type main bearing cap is a highly rigid assembly, helping to resist vibration. A pair of chain-driven balance shafts further smoothes the inherent vibration of a large displacement in-line 4-cylinder layout. A self-adjusting silent-type camshaft chain and a serpentine accessory drive belt also reduce NVH.

With a self-adjusting silent-type cam chain, long wearing platinum-tipped spark plugs and a precision-engineered valve train, the TSX is engineered for low maintenance. Other than routine fluid changes and inspections, the first scheduled engine tune-up is required at 110,000 miles.

One of the standard transmissions in the TSX is a close-ratio 6-speed manual gearbox. With exceptionally short 45 mm shift throws (most European sedans have shift throws of about 60-65 mm) and a precise, light shifting action, this transmission perfectly complements the car's sporting character. With six gear ratios instead of the more common 5-ratio arrangement, the TSX has closely spaced gears for superior acceleration, yet still has a top gear that allows for a low and efficient cruising rpm.

To reduce weight, the compact new transmission case and bellhousing are cast of a special magnesium alloy-the first use of this lightweight material in the transmission of an Acura product. This complex casting is seven pounds lighter than the comparable aluminum version, and is highly rigid to damp out noise and vibration. Inside, the gearbox has multi-cone synchronizers on all gears (including reverse) to reduce shifting effort.

A lightweight clutch with low-inertial mass allows the engine to rev quickly, the clutch pedal stroke is short and the effort is comfortably low. A broad and progressive engagement band makes the TSX easy to launch from a stop smoothly. The clutch incorporates a wide-angle clutch-torsion mechanism that reduces the gear rattling sound that is common in many manual-transmission designs.

To deliver the smoothness and convenience of an automatic transmission, coupled with the performance and sporting feel of a manual gearbox, the TSX offers a 5-speed Sequential Sport-Shift automatic. With five closely spaced ratios, the automatic transmission helps deliver impressive acceleration performance. An advanced Grade Logic Control System and intelligent shift programming combine with new drive-by-wire throttle control to deliver remarkably swift and smooth shifts and intuitively correct gear selection.

The TSX automatic transmission reduces shift shock and improves shift smoothness with the use of an industry-leading linear solenoid direct-acting control. The TSX also utilizes an intuitive 5-position shift gate design.

The SportShift transmission can be operated in two different modes: fully automatic or with driver-selected ratios. In automatic mode, its Grade Logic Control System provides smart ratio selection regardless road gradient. With sensors that monitor throttle position, vehicle speed and acceleration/deceleration, the system compares these parameters with a map stored in the transmission computer. Based on this information, the system can determine if the vehicle is on an incline and adjusts the shift schedule for improved climbing power or downhill engine braking.

To switch SportShift to the manual mode, the driver simply moves the selector lever to a special gate to the left of the "Drive" position. When in manual mode, a forward push of the lever selects a higher gear and a rearward pull selects a lower gear. An LED display between the tachometer and speedometer indicates which of the five available gears is in use.

Shift logic is unique in manual mode, with firmer, faster gear change programming that has a feel similar to that of a manual gearbox. Built-in safety override features make SportShift smarter than any conventional manual transmission, however. Under acceleration, the transmission will hold the selected ratio until commanded to upshift. If the driver doesn't make the upshift in time, the engine ECU will cut off the fuel flow to prevent the engine from over-revving. If the high-rpm condition continues for an extended period even after the fuel is cut (as might be possible on a steep downhill) the transmission will upshift automatically to preclude engine damage. Another important safety feature: The logic will not allow a downshift that would cause the engine to over-rev if the driver selects too low of a gear ratio. To preclude the vehicle starting from a stop in a high gear if the driver inadvertently forgets to downshift, the transmission automatically downshifts as the car decelerates to a complete stop.

To accommodate the high-revving engine's horsepower and torque output, a heavy-duty torque converter is used and the countershaft is constructed of high-strength material. To boost efficiency, the transmission has a low-friction clutch and a special super-thin torque converter. The thin torque converter results in a compact transmission unit. Other space saving measures include a double-row idle gear and a tightly packaged second-gear clutch.

To improve fuel economy and while maintaining a high level of drivability, the 5-speed automatic transmission includes a new generation of active lockup torque converter. With the precise control afforded by a linear solenoid, the system expands the speed and throttle setting range in which lockup can be engaged in the top four gears. The resulting reduction in transmission slippage results in a 2-percent improvement in fuel mileage in both city and highway driving. Due to its efficiency and taller (higher numerically) final drive ratio, the SportShift automatic transmission-equipped TSX actually delivers better fuel economy than does the standard 6-speed manual gearbox counterpart under similar driving conditions.

With the TSX drive-by-wire system, the operation of the automatic transmission and engine are fully integrated, resulting in remarkable shift smoothness, and a significant reduction in shifting time. With this cooperation between engine and transmission, shift time from second to first gear drops from 1.15 second to just 0.7 second-a 40-percent improvement.

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