I ran one (.21) race prepped (not full mod) last season in a variety of buggies- LOVE IT! Had the .24 in my ST-RR and it was too much for all but one track (HUGE with a long straight)- tried it at the Mapston Memorial race and was just too much, I stuck the .21 in and it was money. smooth with lots of top end, My CL7B had a little more grunt on the bottom but a newer lighter truck like the LOSI will like it fine. If I had to complain abiut it my bitch is the Carb, The slide is a little stickier than my Novarossi but that's the case on all my Trinity/ Sirio stuff- works fine you just have to be extra carefull setting up your linkage (watch your bottom idle screw- make sure the slide is open/ extended when you turn it in). Great Motor- I have a fresh one for this season (and the old one still screams with about 5 gallons) Definately a safe purchase,