The CFM56-3B-1 engine was chosen to be the engine for this new 737 type. This engine burned much less fuel and was much less noisy. However, it was also difficult to fit these engines to the aircraft. This was because the 737's wings were not very high above the ground, and the CFM56 had a bigger diameter than the original engines. Boeing and CFM solved the problem by putting the engine slightly ahead of the wing, instead of right under it. They also moved some parts of the engine, which would normally go on the bottom, to the sides. This made the engine look a bit like a hamster pouch, because the engine is not shaped like a circle.