According to FEV GmbH, an independent engine designer, the belt drive lowers fuel consumption compared to the chain, and therefore reduces CO2 emissions. In a 1.6 liter gasoline engine, for example, the belt drive reduces fuel consumption by more than 1% and saves up to 1.5 grams of CO2 per kilometer. "Belt drives are lighter and run a lot more quietly too. Belts don't tend to lengthen either," says Hermann Schulte, head of Timing Belt Development at the ContiTech Power Transmission Group. "A significant advantage, because a lengthening chain alters the engine timing. As a result, consumption increases and performance drops. Emissions levels are quickly exceeded." In endurance tests, a belt lengthened by just 0.1% after 240,000 kilometers of service life - the figure was five times greater with a chain.
..
The advantage of the timing belt in oil is that it has a narrower construction than the dry-running version and it is even quieter. In the case of a crankshaft pulley with 19 teeth, no noise can be detected, even with the engine operating under full load, because the oil not only reduces friction, it absorbs sound as well. This is important for the simple reason that the increasingly popular downsized engines generally run less smoothly.