05 March 2009

Tech Spot: Dropped Pots Not New

OUT There 57 - All Torque

With Honda beating the cylinder deactivation technology drum in their new TV ads for fuel-sipping Accord, you’d think this was the latest thing.

Also known as “Variable Displacement”, the concept has been around in one form or another almost as long as we’ve had cars and engines.

The idea is simple; it involves shutting down banks of cylinders according to engine load to reduce fuel consumption. It works best in V-engines with opposing pairs.

First seriously trialled during WWII, it wasn’t adopted commercially until Cadillac installed a V8-6-4 in their Seville model in 1981. In short it was a disaster and dealers resorted to deactivating the inadequate computer module to run the engines as full-time V8s. Mitsubishi had more success in the ‘90s, but also dropped the idea due to poor buyer response.

Chrysler, Mercedes-Benz and GM are all back in the “multi-displacement” arena now too.

With leaps in computer technology, Honda reintroduced Variable Cylinder Management (VCM) in their J-Series engines powering the award-winning, 8th generation V6 Accord and Odyssey.

Honda’s VCM in the 202kW 3.5-litre SOHC i-VTEC V6 deactivates specific cylinders by using the VTEC (Variable Valve-Timing and Lift Electronic Control) system to close the intake and exhaust valves while a 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 centre cylinders of the front bank operate, and the right and centre cylinders of the rear bank operate.

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