I am an old time RC boater and RC Car racer have used most of their Marine engines including .21 for oval car racing. These engines are really high performance with high rpms that can take a 50-60% nitro fuel (K&B 1000) back in the 70's. These were our top of the line race engines we have used including K&Bs, Webra for our RC hydros, boats and cars and to mention OS Max as well. They have quality and outstanding performance and I can vouch for that.