What blew me away was that the high-end engines[1] turn just a few hundred RPM during a race, which to me seemed ridiculous when you see wall of flames from the headers when they release the car at the line.
Also how they use aluminum for the connecting rods instead of stronger and stiffer metals like titanium, as they can then act as shock absorbers protecting the crankshaft bearings.
Lots of interesting tech to eek out performance and lifetime.
I've been enjoying watching Steve Morris's YouTube channel[2], he shares a lot of such information. He's mainly making drag and drive engines, which has the additional constraint of having to survive thousands of miles of regular roads between races.
I've also enjoyed Brian Lohnes channel[3] for interesting historical accounts from the early days.
[1]: https://en.wikipedia.org/wiki/Top_Fuel#Performance