268 Horsepower 3.5-liter i-VTEC V-6 (EX V-6, EX-L V-6 Sedan; EX-L V-6 Coupe)

Overview
The 3.5-liter SOHC i-VTEC V-6 engine available in the Accord Sedan and Coupe is the largest and most powerful engine ever offered in a Honda passenger car. It builds on technologies that have been developed and refined on previous Honda powerplants. With its 60-degree V-angle, the Accord's V-6 engine is inherently very smooth and has compact overall dimensions that allow efficient packaging within the vehicle. The V-6 with automatic transmission incorporates a new-generation of i-VTEC technology that boosts fuel efficiency using Variable Cylinder Management

i-VTEC with 3-stage Variable Cylinder Management™ (VCM™)
The Accord's available SOHC V-6 with automatic transmission includes i-VTEC with VCM. With the boost in fuel efficiency attributable to VCM, the larger and more powerful Accord V-6 with automatic transmission actually gets better fuel economy than its smaller, less powerful predecessor when tested with the same methodology. Using the EPA's new 2008 methodology, the Accord V-6 Sedan returns EPA-estimated fuel economy of 19/29 City/Highway. That is an increase over the previous Accord V-6 (18/26 City/Highway) of 1 mpg City/3 mpg Highway, when both vehicles are compared with the same 2008 methodology.

VCM Operation
To help improve the fuel efficiency of the V-6 engine available with the 5-speed automatic transmission, a new generation of Honda's VCM is used. This is the first application of VCM on a non-hybrid Accord model. Unlike previous VCM systems that switched between three- and six-cylinder operation, the Accord's system can operate on three, four or all six cylinders.

During startup, acceleration or when climbing hills – any time high power output is required – the engine operates on all six cylinders. During moderate speed cruising and at low engine loads, the system operates just one bank of three cylinders. For moderate acceleration, higher-speed cruising and mild hills, the engine operates on four cylinders.

With three operating modes, the VCM system can finely tailor the working displacement of the engine to match the driving requirements from moment to moment. Since the system automatically closes both the intake and exhaust valves of the cylinders that are not used, pumping losses associated with intake and exhaust are eliminated and fuel economy gets a further boost. The VCM system combines maximum performance and maximum fuel economy – two characteristics that don't typically coexist in conventional engines.

VCM deactivates specific cylinders by using the VTEC (Variable Valve-Timing and Lift Electronic Control) system to close the intake and exhaust valves while simultaneously the Powertrain Control Module cuts fuel to those cylinders. When operating on three cylinders, the rear cylinder bank is shut down. When running on four cylinders, the left and center cylinders of the front bank operate, and the right and center cylinders of the rear bank operate.

i-VTEC V-6 engine rocker arm profile showing quadruple oil passage route on rear valvetrain

The system is electronically controlled, and uses special integrated spool valves that do double duty as rocker-shaft holders in the cylinder heads. Based on commands from the system's electronic control unit, the spool valves selectively direct oil pressure to the rocker arms for specific cylinders. This oil pressure in turn drives synchronizing pistons that connect and disconnect the rocker arms.

Active Control Engine Mount (ACM) and Active Noise Control (ANC)
The ACM system is used to minimize the effects of engine vibration as the VCM system switches cylinders on and off. Sensors alert the Electronic Control Unit (ECU) to direct ACM actuators positioned at the front and rear of the engine to move to cancel engine vibration. Inside the interior of the Accord, the ANC system works in cooperation with the ACM system to further reduce any sound relating to the function of the VCM system. (Please see the Interior tab for more information.)

V-6 High-Flow Exhaust System
The Accord V-6 has a completely new exhaust system to accommodate its larger displacement and increased power output. Tubing diameter has been increased and new dual silencers are used. In total, the changes provide a 38% increase in exhaust flow compared to the previous V-6 system.

3.5-liter VTEC V-6 (Manual Transmission EX-L V-6 6MT Coupe)

Overview
The Accord V-6 Coupe with 6-speed manual transmission uses a unique version of the 3.5-liter V-6. In place of the i-VTEC cylinder heads that incorporate Variable Cylinder Management (VCM) technology for enhanced fuel economy, the performance-oriented 6-speed V-6 Coupe has VTEC cylinder heads that operate all six cylinders under all driving conditions. The engine switches between two different intake valve profiles based on the operating conditions to deliver superior low- and mid-range power, while achieving the same peak 268 horsepower and 248 lb-ft. torque figures found in the automatic transmission version with VCM. The engine also features a variable intake manifold (constructed of lightweight magnesium) to improve low- to mid-range torque.

VTEC® (Variable Valve Timing and Lift Electronic Control)
VTEC® operates the engine's 12 intake valves in two distinct modes. At low engine speeds, the intake valves follow low lift and relatively short duration cam profiles. At high engine speeds the valves switch to high-lift, long-duration mode to deliver the best volumetric efficiency. The V-6 with 6-speed manual transmission has a VTEC changeover point that occurs at approximately 5000 rpm.

Intake and Exhaust Tuning
The intake and exhaust systems on the Accord Coupe V-6 with six-speed manual transmission feature exclusive intake and exhaust tuning for sporty sounding performance. The intake is designed to resonate a unique performance sound at mid and high rpms, while the exhaust is designed to convey a low, powerful note at low to mid rpm.

3.5-liter VTEC V-6 Intake and Exhaust Tuning