All I do is race and I just started running a big series here in Georgia, which is 8 rounds at 3 different tracks. I have well over 3 gallons on my D21B and still have to loosen the glow plug when I start it cold. Going to get another STS but the race budget right now only allows for another standard D21B. If I can get up the difference I would like to get the RBmod D21B. But my stock D21B has no problem keeping up with much higher priced engines!!!!!!!!!!!!!!!!!!!