Road and Track, July 1st, 2006
Few eyebrows were raised when Acura announced it was coming out with a new premium entry-level SUV. “We needed something different,” explained Nobu Takahashi, lead powertrain engineer for the RDX. And so she delivered.
That’s right; Takahashi san not only is Honda’s first female lead engineer, but also the main sourceof ingenuity behind the RDX’s clever variable-flow turbo charger system. The 2.4-liter aluminum inline-4 out of the TSX serves as a starting point for the engine architecture, but few internal similarities remain between the two as the RDX engine is purpose-built. The 2.3-liter, 16-valve powerplant retains i-VTEC (intelligent Variable Valve Timing and Lift Electronic Control) on the intake side, while compression has been lowered to 8.8:1 to accommodate the 13.5 psi of air forced into the cast-in iron-lined cylinders.
Boost pressure is optimized in the system via an infi nitely variable, ECU-controlled nozzle in the turbo housing that regulates the flow of exhaust gases through one of two channels acting upon the turbine. At low rpm when exhaust gas is at a minimum flow, the Flow Control Valve is completely closed, allowing the maximum amount of pressure through the small inner channel. As revs increase toward wide-open throttle, the Flow Control Valve continues to open until it reaches its maximum flow capacity. With this type of exhaust control, boost comes in as early as 2000 rpm while maximum boost is realized at 2500 rpm all the way through 4500 rpm.This translates into an engine with power characteristics much like a 6-cylinder (240 bhp at 6000 rpm, 260 lb.-ft. at 4500 rpm) but with better fuel mileage (estimated
EPA 19/24 mpg) and a much cooler sound.
The RDX sits on a brandnew light-truck platform rolling out of Acura’s Marysville, Ohio, plant but there is nothing inherently trucklike about its handling. This can be attributed partially to its sporty suspension, which has MacPherson struts in front and a multilink rear.More signifi cant is the
RDX’s version of the SH-AWD (Super Handling All-Wheel Drive), the active power delivery system that varies torque to individual wheels fore and aft as well as laterally, depending on road/vehicle conditions. The system allows for a transfer of torque up to 90 percent to the front and 70 percent to the rear, while rear torque can be biased 100 percent left or right through electromagnetic clutch packs. This apportionment of torque allows the RDX to yaw itself out of corners while under power, resulting in better vehicle balance and control.
In rainstorm-plagued San Francisco, California, we sampled the new SH-AWD-equipped RDX on some great roads leading up to Sonoma County. Controlling the 5-speed automatic transmission via steering-wheel-mounted paddles made it easy to select an appropriate gear for a corner, but it does not rev-match on downshifts to aid smoothness. Where you would normally expect an SUV weighing nearly 4000 lb. to understeer, the RDX has grip all the way to the exit. Only in very tight corners did the RDX “push” the laws of physics.
Although not meant to be a family hauler, the RDX has enough space and standard comfort features for a weekend getaway for four. Some of the extras you can specify include the Acura Navigation System with AcuraLink real-time traffic, and an upgraded 410-watt, 10-speaker ELS surround sound system—a couple of premium features included in the Technology Package. Although an exact starting price was not released at press time, expect the new RDX to cost between $30,000 and $37,000. That might raise a few eyebrows when they arrive at dealers in June.
