Here is a video of a car with a typical noisy quick change. All the cars in this video are powered by flathead Ford engines of 286 ci or less. The car with the camera is probably the fastest vintage modified running these days and it has an engine that would have been classed as a street engine in the 50's. Notice the vacuum gauge at various points on the track. He is not getting to full throttle till half way down the straight. (too much hp for the legal tire size) Tach says 6200 max.
Lots of hp left on the table but if you win all of the races, why spend for more?
https://youtu.be/49mknw1Fkfg