Hey all! Pardon my newbieness with nitro engines, but I'm a bit confused about the differences between the .12, .15, and .21 engines for the RC10GT2 which I intend on buying. First of all Associated claims the .15 is best for backyard bashing, which I would understand because it's that much more powerful then the .12. However, they recommend the .12 for racing! Is that because since the car will never reach top speed or be over-torqued anyway, the .12 is more fuel effecient and/or lighter? Or is the difference more than just in HP? I had assumed that the RPMs would be the same between the three engines, and just the HP would change, but is this correct at all? Also, where does the .21 fit into any of this?