Crank case size typically is the difference between a "small block" and a "big block". Again, typically, big blocks are .21ci on up while small blocks are .18ci on down.
Example:
Top engine is a .21ci big block. Bottom engine is a .18ci small block. The crank case on the BB is longer/wider, so in general bigger.
There are a quite few "mid-block" engines that are generally .21ci and up, (
Picco .26 maxx for one) but retain the footprint of a small block so you can shoehorn a lot more torque into a vehicle without a conversion kit. Many were made specifically for the t-maxx and revo as the original 2.5 engine had just barely enough power to make them fun.
Traxxas finally realized this and spit out the 3.3 which is a good balance of power and RPM's that can push their MT's around much better. This adds a .19 or .20 to the mix in the small block crank case. Losi also has one now that is a spitting image of the 3.3 for the speed-nt branded as a
3.4 to compete with the 3.3 jato. Really looks like they took a 3.3 and stamped their logo on the side and dipped the head to me. Maybe shaved a few microns off the piston top and head button just to call it a 3.4 vs a 3.3...
Personally, I can't hardly control a jato with a 2.5R in it... would just be silly with a 3.3 in the thing!