I ran mine without pressure and had a sT60 Carb for my conversion It is a suprisingly quiet running engine as you reall can load it up to the size props that you might use an a 4.2 gas. A 24.8 was in the high 5's to 6K and the idle was under 1k. It is cold blooded so give it time to warm up or you will probably end up over compresses, i used a Su;;ivan Dynatron to start mine but i never ran it as a glow so it was a long time getting run in. The companion Quadra 50 conversion had a sportster 65 carb and turned the same rpm as the ST.
Dennis