Low Rolling-Resistance Tires

Both the Insight & Prius use low rolling resistance tires to improve efficiency. In fact, both use the same tire model, Bridgestone Potenza RE-92s, though in slightly different sizes.

A big part of the low-rolling resistance tire is reducing deformation as tire rotates - by using relatively low profile tires and fairly high pressure. The Insight takes this slightly further, using 165/65R14 format, and recommended tire pressures of 38 PSI front, 35 PSI rear, as compared the the Prius's 35/33 PSI pressures.

Gasoline Engine Technologies

Even the gasoline engines in the Insight and Prius are designed for very efficient and clean operation. Emissions are reduced using precise control over things such as spark timing and fuel injection on a per cylinder basis. Both engines use their respective company's variable valve timing technology, and both incorporate significant friction reduction elements.

However, there is one major way in which the two companies took different approaches to improving the engine's efficiency.

Unlike most cars, including the Insight, the Prius uses the Atkinson cycle, where the exhaust valve doesn't close until after the upward stroke has begun. This effectively results in a higher expansion ration than compression ratio. The Atkinson cycle improves overall efficiency, though it does so at the cost of power.

The Insight takes a different approach to improving the gasoline engine's efficiency, by operating the engine at very lean air-fuel ratios when less power is needed. Unlike most cars, including the Prius, which operate at a "stoichiometric" air-fuel ratio of 14.7:1, the Insight is designed to operate at air-fuel ratios as lean as 22:1.

Advanced Catalytic Converters

Both the Insight and Prius include special catalytic converters to reduce smog-forming emissions.

In addition to improving efficiency, the Insight's lean burn technology allows it to reduce HC and CO emissions. However, lean burn conditions normally results in high NOx emissions. The Insight deals with this by using a special lean-NOx catalyst that converts NOx to less harmful CO2. Overall, this system reduces HC, CO and NOx emissions, the three things measured by the California xxLEV standards, to very low levels.

Rather than using lean burn technology to reduce HC emissions, the Prius uses a special HC catalytic converter. This catalyst captures unburned HCs after a cold start of the engine, when HC emissions are normally at their highest.

The Insight takes a different approach to lowering cold-start emissions, by instead getting catalyst up to temperature quickly. Insight's unique integrated head/exhaust manifold help to get engine up to operating temperature quickly, and 3-way catalyst is attached directly to the head/exhaust manifold so that it will heat up more quickly.

When first started, both cars will initially keep the gasoline engine running to get the catalytic converters up to temperature as quickly as possible.

To reduce emissions of evaporated fuel, the Prius uses a unique resin-bladder fuel tank that isolates the fuel from the air in the tank. Insight also uses plastic fuel tank for weight savings, but doesn't have bladder. Insight does, however, have on-board refueling vapor recovery system.