car engine

Hello everyone, hope to learn more about cars here. I am interested in car engine and transmission system. Especially the carbon deposits. Thanks

I'm interested in old cars. Not necessarily vintage cars but the cars from 70's, 80's and some even 90's. However, the problem is with their engines. They devour gas like an ogre. Like having a mileage of just 8km/ltr. I want to know what are some modifications that can be applied to these...