Bifurcations and chaos can be found in autonomous three- and four-dimensional systems. Concepts like hyperbolicity, normal hyperbolicity and fractal dimension of chaotic sets are important tools to study such systems. A relatively easy way to determine a fractal dimension is the Kaplan-Yorke calculation that uses Lyapunov exponents; we discuss the basic drawback of these calculations. It is remarkable that KAM theory can be extended to dissipative systems in cases with symmetries. We demonstrate this for two different systems of the Jafari-Sprott-Golpayegani project. Torus bifurcations and chaos can be demonstrated in several coupled second-order systems involving parametric and self-excited systems