please explain this to me is it the engine size that they are talking about like if i have a thunder tiger 21 what would this chart mean to me is this speaking about the engine size in the outer diameter or is it something that will do with speed and power..
Typical RC Engine Displacements

Common RC engine displacements range from about .12 to .46 and larger. These numbers that begin with a decimal point are the displacement in cubic inches. Sometimes the abbreviation ci is appended to the measurement. But just remember that a .18 engine is actually .18ci or .18 cubic inches of displacement.
That same .12 to .46 range, expressed in cubic centimeters would be approximately 1.97cc to 7.5cc of displacement. You can use an online conversion tool to quickly convert from cc to ci or ci to cc. Here's a small reference list (cc is rounded) to give you an idea of how cubic inches compare to cubic centimeters:

.12ci - 2.0cc
.15ci - 2.5cc
.18ci - 3.0cc
.21ci - 3.5cc
.25ci - 4.1cc
.27ci - 4.4cc
.32ci - 5.2cc
.36ci - 5.9cc
.46ci - 7.5cc
so what do the ci and cc exactly mean in simple English terms please thank you

the engine displacement is the swept volume of the piston in the cylinder, from the bottom to the top of it's travel, it is a simple calculation using the diameter of the piston and the length of the stroke (distance from the top to the bottom of the piston stroke)

so do tha mean more power? hp? or anything?

More cc or CID means more torque.

ok thank you for your info GUYS. but 1 more thing i dont know if you are familiar with the mgt truck but it has a 8.0 engine and the other truck has a axial 28 engine. what would have more torque the axial or the 8.0 being all stock but the engines

i have a MGT 8.0 and i have to replace the front driveshaft do to a little "crash", however i have been driving it in 2 wheel drive mode and i no notice that it will not go into 2nd gear, so could only having 2 wheel drive cause that? Also, i have been trying to find the factory settings for the engine (lost my book) due to the fact i just think i have been "tuning" on it to much and so i am just really trying to start over with it.