traxxas names their engines by 3.3 and 2.5 so they look "big" and tricks u into buying there engine over the others but its only a little .15 and a .18 size engine...but..smaller cc engine have MORE RPM than bigblock engines....a .12 size engine will outrun a .28 in the high rpm but the .28 will have aLOT more torque

big engine = lots of torque/less top RPM/more HP
small enigne = less torque/more top RPM/less HP

but there are some big block engines like the collari .25 and the .32 wich produce over 36,000 RPM...i think lol..i know hte .25 produces around 40,000 somthing