The orks un 40k they make their technology and other things work just by believing that it works, if they believe that a vehicle will go faster by painting it red it will go faster even if it doesn't have an engine.

It doesn't quite work to that extreme. The wartrukk will still need an engine. Maybe not a particularly good or reliable engine, but an engine none the less.

The Orks belief in their equipment fuels a gestalt field known as the WAAAAAGH which will slightly bend reality to make the Ork's ramshackle weapons and vehicles actually work somewhat reliably. A red painted vehicle will be a bit faster because the Orks believe it. A blue on will be more lucky. A black one will be tougher.