Whatever be your vehicle a car, truck or an SUV, every one of us want to have it deliver good mileage and thus save us some money on our monthly budget. These gas saving devices are ample in numbers on the market and they give many promises that they save fuel efficiently. However, they are still left without proper evidence, however, still people keep trying these gas saving devices. The fuel savers work on the principle that they increase the combustion of fuel in the engine. However, the real fact is that engines lack the efficiency to transfer the heat to mechanical energy, i.e. transmission. Concentrate on gas savers that improve the transmission rate then you can save some money effectively.