2006 Honda Ridgeline - Powertrain


The 2006 Honda Ridgeline's engine, transmission and four-wheel drive system are designed to handle medium duty payloads and towing or off-road driving with toughness, efficiency and agility. Respected worldwide for its ability to build engines that are both powerful and environmentally sensitive, Honda's 3.5-liter V-6 engine in the Ridgeline is no exception with high-output performance, a good level of fuel efficiency and ultra-low emissions. The standard 5-speed automatic transmission integrates design features to make towing uncomplicated from an equipment standpoint - just add a Honda accessory hitch and a quick connect electrical harness, then tow a properly equipped trailer weighing up to 5,000 pounds. The fully automatic Variable Torque Management 4-wheel drive (VTM-4) system provides confident, decision-free operation in rain, snow, ice, sand and mud, while also improving on-road and towing performance.

Compared to any other Honda vehicle, exclusive Ridgeline powertrain components include a high-mounted fresh air intake, tuned induction, standard automatic transmission fluid and power steering fluid coolers, a high capacity radiator with dual electric fans, a low final drive ratio, increased VTM-4 torque transfer and high capacity transmission components.

2006 Honda Ridgeline Powertrain Highlights:


  • 3.5-liter 60-degree V-6 with belt-driven single-overhead camshafts and four valves per cylinder
  • 255 horsepower @ 5,750 rpm and 252 lb.-ft. of torque @ 4,500 rpm
  • Variable Valve Timing and Lift Electronic Control (VTEC)
  • Drive-by-Wire throttle system
  • Computer-controlled Programmed Fuel Injection (PGM-FI)
  • Dual-stage intake manifold
  • Direct Ignition system
  • High-mounted fresh air intake
  • 105,000-mile tune-up intervals

5-speed Automatic Transmission

  • Wide-ratio design provides a first gear with extra pulling power to start heavy loads in combination with a high top gear for efficient highway cruising
  • High capacity components are engineered for towing, heavy payloads and off-road use
  • Standard ATF cooler (no additional ATF cooler needed for maximum tow rating)

Variable Torque Management 4-Wheel Drive (VTM-4)

  • Fully automatic operation provides confidence in all driving conditions
  • Lock feature for getting unstuck in slippery conditions

Fuel Economy and Exhaust Emissions

  • EPA estimated fuel economy ratings of 16 mpg in city driving and 21 mpg on the highway
  • Exhaust system uses two close-coupled primary catalyzers, and an underfloor secondary catalyzer
  • Standard Federal Tier 2, Bin 5 emissions and LEV-2 ULEV California emissions

Fun-to-Drive Performance with Towing and Hauling Capabilities

The Ridgeline's engine has been tuned to provide good performance in everyday driving situations and high-demand situations alike with a broad and flat multi-stage powerband. By combining the advanced engine technologies of VTEC with a dual stage intake manifold, a three-stage torque curve is produced that maximizes the engine's torque output at low, middle and high RPMs. This translates into good off-the-line performance with generous power being delivered right at throttle tip-in and all the way up to the engine's redline. The Ridgeline has the power to get a heavy trailer moving, confidently pass a vehicle on a two-lane road or pull onto the freeway with authority.

Engine Architecture

The Honda Ridgeline's engine is an advanced transversely-mounted 3.5-liter, SOHC, 24-valve, 60-degree, V-6, aluminum-block-and-head design that is compact, lightweight and powerful. A long list of technologies has been engineered to provide 255 horsepower, a unique three-stage torque curve, very low emissions, high fuel efficiency for a truck, and instantaneous throttle response. The VTEC valvetrain and dual-stage intake manifold optimize cylinder filling efficiency across the engine's entire operating range while also enhancing low end torque. Low-restriction intake and exhaust systems, a 10.0:1 compression ratio, and roller-type rocker arms also aid efficiency.

Engine Block

The Ridgeline's 3.5-liter die-cast engine block is made from heat-treated aluminum to minimize weight. A deep-skirt configuration rigidly supports the crankshaft, minimizing noise and vibration. Thin-wall, centrifugally cast iron liners help reduce overall weight. Each liner's rough as-cast exterior surface bonds securely to surrounding aluminum during the manufacturing process to increase strength and enhance heat transfer.

Crankshaft, Connecting Rods and Pistons

A forged-steel crankshaft is used for maximum strength, rigidity, and durability with minimum weight. Instead of bulkier, heavier nuts and bolts, connecting rod caps are secured in place with smaller, high-tensile-strength fasteners that screw directly into the connecting rod. Short-skirt, cast-aluminum, flat-top pistons are notched for valve clearance and fitted with full-floating piston pins.

Cylinder Head

The Ridgeline utilizes innovative cylinder heads that include tuned exhaust manifolds as an integral part of the casting. Made of pressure-cast, low-porosity aluminum, these lightweight components improve overall packaging, enhance exhaust flow and permit optimal positioning of the primary close coupled catalytic converters.

Unlike many trucks, the Honda Ridgeline has four-valve combustion chambers, the best approach to optimum performance with excellent fuel efficiency and very low emissions.

Valves are clustered near the center of the bore to minimize combustion chamber volume and to provide ample squish area. A 10.0:1 compression ratio helps maximize thermal efficiency, power output, and fuel mileage. One centrally located camshaft per bank is driven by a fiberglass-reinforced toothed belt. Head gaskets are made of high-strength materials to contain combustion pressures.

Variable Valve Timing and Lift Electronic Control (VTEC™)

The Ridgeline's innovative Variable Valve Timing and Lift Electronic Control (VTEC) is one key to maximizing engine output across the full operating range. The high-rpm induction lobes of the camshaft provide additional valve lift to help increase peak horsepower. Ordinary engines have fixed valvetrain parameters - the same timing of valve lift and overlap whether the tachometer needle is struggling to climb out of the low-rpm range or screaming at the redline. The VTEC approach, however, has two distinct modes so that operation of the intake valves changes to optimize both volumetric efficiency (breathing) and combustion of the fuel-air mixture. In order to achieve the optimum volumetric efficiency in the lower portion of the engine's operating range, rocker arms are programmed to follow cam lobes that provide low lift and reduced duration (shorter time open with less valve lift).

At 4400 rpm, the Ridgeline's powertrain control module commands the VTEC system to switch intake valve operation to the high-rpm mode. In response, an electric spool valve opens to route pressurized oil to small pistons within the intake-valve rocker arms. These pistons then slide to lock the three rocker arms provided for each cylinder together. As a result, both intake valves follow a central high-lift, longer-duration cam lobe. The switching process takes just 0.1 second and is undetectable by the driver.

The extra lift and longer duration provide the added air and fuel the engine needs to produce high peak horsepower and a broader torque band. Instead of a peaky engine, the Ridgeline has a powerplant that provides excellent performance at any engine speed whether it's towing a boat, hauling a load of gravel, or just getting on the freeway.

Dual Stage Induction Manifold

The induction system atop the Ridgeline's V-6 engine works in concert with the VTEC valvetrain to significantly boost torque across the engine's full operating range. Internal passages and two butterfly valves commanded by the powertrain control module are configured to provide two distinct modes of operation. The valves are closed at lower rpms. In this mode, the three cylinders on each bank draw air from only the nearer half of the manifold's internal chamber, or plenum. The volume of the plenum and the length of inlet passages are both tuned to maximize the resonance effect, wherein pressure waves are amplified within each half of the intake manifold at certain rpm ranges. The amplified pressure waves significantly increase cylinder filling and the torque produced by the engine throughout the lower part of its rpm band. Funnel-shaped intake ports - similar to those used on racing engines - are built in at the uppermost end of each intake runner to improve air flow.

As the benefits of the resonance effect dwindle with rising rpm, the butterfly valves open at approximately 3700 rpm to interconnect the two halves of the plenum, doubling its volume. An electric motor commanded by the powertrain control module directly opens and closes the connecting butterfly valves. Now each cylinder draws intake air from the full plenum chamber. The inertia of the mass of air rushing down each intake passage helps draw in more charge than each cylinder would normally ingest. This phenomenon is the same effect produced by a low-pressure supercharger. The inertia effect greatly enhances cylinder filling efficiency and the torque produced by the engine at higher rpm. Concurrently, the VTEC system has switched from low-speed to high-speed valve timing to further enhance air flow through the intake valves and into each cylinder.

The net effect of the Ridgeline's dual-stage intake manifold and VTEC valve train is that Ridgeline delivers more than many of the large V-6s and small V-8s used by the competition, while also providing superior fuel efficiency and very low emissions. More than 90-percent of peak torque is available from 2500 to 5500 rpm.

High-Mounted Fresh Air Intake

The Ridgeline has a high-mounted fresh air intake system that reduces air intake temperatures to help improve low-end torque while protecting against water intrusion into the engine. To supplement good off-road and towing capabilities, the fresh air intake is mounted just above the front bulkhead (underneath the front of the hood.)

Programmed Fuel Injection

Fuel is delivered in sequence and timed to each cylinder's induction stroke by six injectors mounted on the lower portion of the intake manifold. These injectors optimize the fuel spray pattern, and improve fuel atomization for increased fuel mileage and reduced emissions. A 32-bit, 80MHz central processor unit (CPU) within the Ridgeline's powertrain control module calculates injection timing and duration after assessing an array of sensor signals: crankshaft and camshaft position, throttle position, coolant temperature, intake manifold pressure and temperature, atmospheric pressure, and exhaust-gas oxygen content. The CPU controlling the Ridgeline's Programmed Multi-Point Fuel Injection (PFM-FI), VTEC valvetrain, dual-stage intake manifold and the transmission also communicates with CPUs that regulate the drive-by-wire throttle, the Variable Torque Management 4-wheel-drive system and the Vehicle Stability Assist (VSA).

Drive-by-Wire Throttle

The Ridgeline features an innovative drive-by-wire throttle system that replaces a conventional throttle cable arrangement with an all-electronic system that senses the throttle pedal position and relays that information to a computer. The computer then performs the actual throttle activation instantaneously. The Ridgeline's drive-by-wire system works by means of a throttle pedal sensor, a throttle angle sensor, an electronic control unit and a DC motor to control throttle opening and provide fail-safe throttle operation. This system allows for throttle control to be integrated into the VSA and VTM-4 systems and also incorporates the cruise control function. To improve shifting smoothness, the drive-by-wire system controls the throttle during transmission shifts. To maximize driving feel, throttle pedal characteristics are calibrated to be smooth and linear during start up, when driving on ice or other low traction surfaces, and more responsive during acceleration.

Direct Ignition System and Knock Control

Maintaining the correct ignition timing throughout all operating conditions is essential to producing maximum power, using fuel efficiently and minimizing emissions. A powertrain control module (PCM) examines various engine functions as well as a block-mounted acoustic knock sensor to determine optimum ignition timing. In relation to octane rating of fuel, the PCM retards ignition timing as needed to forestall detonation. As a result, the engine constantly operates at the point of peak efficiency. Spark is supplied to iridium-tipped, long-life spark plugs by six coil units positioned directly over the plugs in the cylinder-head access bores.

105,000 Mile Tune-Up Intervals

Before 105,000 miles of driving, the only maintenance necessary is routine inspections and fluid and filter changes. At 105,000 miles, the valves should be adjusted, the timing belt should be replaced, the water pump should be inspected and the iridium-tipped spark plugs should be replaced.

Exhaust System

The Ridgeline employs a high-flow single exhaust system that helps to generate additional horsepower while still maintaining strict emissions standards. A low-restriction, high-flow exhaust system is crucial to efficient power and torque production. The Ridgeline features a high efficiency system that incorporates several key elements that work in concert with the engine's uniquely designed cylinder heads to help boost performance, reduce tailpipe emissions and trim weight. Major system components include two close-coupled catalytic converters, a secondary underfloor catalytic converter, a centrally positioned, high-flow resonator and a silencer. The close coupled catalytic converters provide almost double the surface opening of the single underfloor unit they replace and mount directly to the cylinder head to reduce light off time, thereby allowing the catalyst to begin cleansing the exhaust as soon possible. The catalysts, muffling element, and piping are all sized for high flow and low restriction. High-chromium stainless steel is used throughout the exhaust system for excellent durability.

5-Speed Automatic Transmission

The Ridgeline features a compact 5-speed automatic transmission that utilizes a 4-shaft design layout. This configuration, together with a super flat torque converter allows for a compact transmission design. This unit's design utilizes wide gear ratios, which enhance low-speed pulling capability and the ability to cruise efficiently on the highway.

A lock-up torque converter helps maximize fuel efficiency. Torque-converter lock-up and shift timing are both managed by a 32-bit, PGM-FI CPU that maintains a communications link with the engine's CPU.

Creative use of clutched idler gears permits the transmission to provide five forward speeds with little more weight or bulk than a typical four-speed automatic. A one-way clutch is provided for first gear to smooth upshift quality.

The Ridgeline has the highest tow rating of any Honda vehicle. In response, powertrain engineers further enhanced transmission capabilities. Gear and shaft materials, as well as the transmission case itself, are all engineered to support towing, off-road, and payload hauling needs. A direct-control strategy provides real-time pressure management of the transmission's clutches. Various safety and control strategies coordinate engine and transmission operation. For example, driveline shocks during up- or downshifts are minimized by momentarily reducing engine torque during the shift. For driving through hilly terrain, a Grade Logic Control system monitors throttle position, vehicle speed, acceleration and deceleration to avoid hunting and excessive shifting. A lower gear is held for a longer-than-normal period to provide better climbing ability on hills and more engine braking on downhill grades.

Automatic Transmission Cooler and Power Steering Cooler

The Ridgeline provides "simplified towing for everyone" by including a large ATF cooler as standard equipment. An ATF cooler contributes to long-term reliability by keeping damaging heat out of the transmission. Often an option, most vehicles used for towing require a transmission cooler in order to properly utilize the maximum advertised towing capacity. The Ridgeline's standard ATF cooler is mounted in front of the engine's radiator. Also related to towing and heavy payloads, the Ridgeline features a power steering cooler to help dissipate power steering fluid heat build up that can occur when hauling heavy loads or towing (see the chassis section for more information).

Variable Torque Mangement 4-Wheel Drive System (VTM-4™)

After studying various all-wheel- and four-wheel-drive systems offered by the wide variety of pickups on the market today, Ridgeline engineers concluded that virtually every one had functional shortcomings and was undesirably bulky and heavy. The direct result of that research was to use Honda's innovative fully automatic VTM-4 system. This fully automatic 4WD system is the best match for the Ridgeline owner and proactively distributes torque to all four wheels as needed. This system provides front-wheel drive for dry-pavement cruising conditions and engages all-wheel drive when needed to improve stability or maneuverability. Unlike many competitive systems that use an engagement strategy triggered by wheel slippage, the Ridgeline's VTM-4 system anticipates the need for all-wheel drive and engages the rear wheels before slippage begins. Additional torque is redistributed to the rear for improved performance during acceleration, especially on low friction surfaces and during towing. In addition, the VSA system provides a limited-slip differential effect by applying braking force to a slipping front wheel thereby directing driving force to the wheel with more grip.

Another special feature is a "VTM-4" lock button, located on the instrument panel, which temporarily holds engagement of both rear wheels to aid traction

VTM-4 Modes of Operation

There are three distinct modes of VTM-4 engagement. The first - called the acceleration torque control (ATC) mode - is unique to this system. It works even on dry pavement to proactively distribute driving torque to all four wheels as the Ridgeline accelerates from a stop to cruising speed. One notable benefit of this mode is that traction is immediately available to move the vehicle from rest through a slippery intersection before slippage occurs. (Once a wheel slips, the traction available for forward propulsion and lateral restraint is significantly diminished.)

A second advantage is that apportioning drive torque among all four wheels greatly diminishes the likelihood of torque steer. Handling dynamics are also improved. Reducing the propulsive force carried by the front tires leaves more adhesion for steering the vehicle into a tight bend or for holding cornering arc in the middle of a turn. In other words, the Ridgeline's dynamic balance is greatly enhanced by ATC logic.

Rear wheel torque rises smoothly from zero to the optimum setting in proportion to vehicle acceleration (both forward and reverse). At higher speeds, the front wheels are capable of providing the desired thrust with excellent handling so torque delivered to the rear wheels automatically diminishes with speed. While cruising, all driving torque is delivered by the front wheels in the interests of smoothness, quietness, and fuel efficiency.

The second engagement mode uses wheel slippage control logic. If the difference in rotational speed between front and rear wheels rises because of a slippery surface or poor traction at the front of the vehicle, that condition is detected by wheel-speed sensors which are monitored by VTM-4's ECU. In response, the ECU commands an increasing amount of torque for the rear wheels. Torque is proportional to both slip rate and the rate at which the slip rate is increasing. This operation is similar to conventional slip-based all-wheel-drive systems already on the market.

The third mode of all-wheel-drive engagement activates when the driver presses the lock button mounted on the instrument panel. The maximum amount of rear-drive torque is locked in until the vehicle gets moving and exceeds six mph, at which time rear drive torque is gradually diminished. By 18 mph, the lock mode is fully disengaged. When vehicle speed drops below 18 mph, the lock mode automatically reengages. The shift lever must be in the first, second, or reverse-gear position to use the lock mode.

The maximum torque delivered to the rear wheels allows the Ridgeline to claw up a 28-degree (53-percent slope) dirt grade. On a split-mu (split-friction) grade (different amounts of traction at each wheel), VTM-4 automatically provides sufficient rear-wheel torque to help the vehicle climb steep and slippery terrain such as a steep driveway with patches of snow and ice.

Propeller Shafts and Half Shafts

The two-piece propeller shaft that carries drive torque from the transfer case to the rear-drive unit is made of high-strength steel tubing to permit a smaller diameter, thereby improving both ground clearance and interior room. The cross yokes attached at each end by friction welding are forged steel for high strength and low weight. The center support bearing is rubber isolated to block the transmission of driveline noise from the interior of the vehicle. A low-friction plunge joint located near the center of the propeller shaft accommodates relative motion between front- and rear-mounted driveline components. A tuned-mass damper inside the front portion of the propeller shaft cancels any bending tendency in response to powertrain vibrations.

Equal-length, front-wheel half-shafts have a plunge joint at their inboard end and a ball-type universal joint at the wheel end. Rear half-shafts are similar in design but use a double-offset joint at the inboard end and a ball joint at the outboard end. All universal joints are constant-velocity type.

VTM-4 Rear Differential

The Ridgeline's rear axle unit does not use a conventional differential. Instead, a hypoid ring-and-pinion gear set supported by a cast-aluminum housing switches torque from the propeller shaft's longitudinal orientation to the lateral orientation necessary to drive the rear wheels.

A connection from the ring gear to each wheel's half-shaft is made by left- and right-side clutches. Each drive clutch consists of three elements: an electromagnetic coil, a ball-cam device, and a set of 19 wet clutch plates which are similar in design to clutches used in an automatic transmission. Ten of the plates are splined (mechanically connected) to the ring gear while nine of the plates are splined to a half shaft. Left and right clutches are identical.

The VTM-4 system's electronic control unit (ECU) determines torque which is to be distributed to the rear wheels, then electric current is sent to the two electromagnetic coils. The resulting magnetic field moves a rotating steel plate toward each fixed coil. Friction between that steel plate and an adjoining cam plate causes the cam plate to begin turning. As it does, three balls per clutch roll up curved ramps, creating an axial thrust against a clutch-engagement plate. This thrust force compresses the wet clutch plates, thereby engaging drive to the corresponding rear wheel.

Unlike mechanically actuated four-wheel drive systems, the VTM-4 system is infinitely variable. The amount of torque provided to the rear wheels is directly proportional to the electric current sent from the ECU and can be adjusted from zero to a preset maximum. This current constantly changes to deliver the optimum rear torque calculated by the ECU. An internal gear pump circulates VTM-4 fluid to cool and lubricate the clutches, bearings, and gears within the rear drive unit. Use of high-strength, low-weight materials - such as die-cast aluminum for the housing - minimizes the bulk and weight of this hardware, helping to keep the weight of the entire all-wheel-drive system to about 212-pounds.