Ive ran os, novarossi, and go.
I liked go but you couldnt rely on them to finish the race, the tune was very inconsistent.
I went to os. Crazy amount of power, so so run time, but you had to replace the rod often to avoid killing your engine. The speed was better on the rod but at 500$ a pop ill pass
Then and now i am with novarossi. Ive ran the +4, +4c and the toro nero. This is a great engine. Crazy amount of power but its controlable. its sutable for both the buggy and a truggy. The runtime is fantastic. Tune is very consistent. I dont see me going to another manufacturer anytime soon