Most of the SPA airplanes were the "ballistic designs" with retracts no less. Take a look at the list: Phoenix 1-8, Dirty Birdy, Deception, A-6 Intruder, Curare, UFO, Mach 1...Hence all the interest in the SPA from folks like myself who started with a dirty birdy powered by a muffled enya (no pipe...) Guess what, it was loud.
Go to an event. These are not popular planes. I think they went as far as 1976 just to be more accomadating. Maybe they should change it to stop at 1972 instead of 76, now that you can get Daddy Rabbit and Chaos kits.