Information borrowed from XHeli.com. Place here so I can easily print it.
The 450TH is widely accepted as a great T-Rex helicopter motor, extreme speed in Wings and Jets. The 450F is still undergoing testing but well liked by all helicopter guys. Having a 2.3mm axle for helicopter’s makes it very versatile and useful in gearboxes for planes upto 4 lbs and since you can slide off the bell the 450F is easily modified to a 2250 KV pusher or tractor for direct drive or left at 3450 Tractor or pusher. The lower KV motor is known as the 450FT. I don’t recommend use of the 450F direct drive on Jets and Wings as it spins just too fast, the 450TH is about the upper limit for direct drive on a decent size 6 inch prop. The mod to this motor will enable you to run a 7×5, 8×5 prop with authority. See the data on the 450FT technical page .
Many of you have been asking "What Motor for a specific plane or helicopter". I am thinking of putting together a motor selection guide but for now let’s see if I can provide some information that will help.
Quick rule of thumb – 100-120 Watts per pound provides an excellent experience.
Up to 1 pound plane use : 300DF, 300ST, 400ST, 400T
Up to 2 pound plane use : 400F, 400DF, 450XT
Up to 3 pound plane use : 450TH, 450F, 450FT
T-Rex Heli – 450TH on 13T 3.17mm, or 450F on 10T 2.3mm pinion. For longer run time and less power – 400DH on 9T, 2.3mm.
Shogun Heli – 400DH – 8T pinion
3D Pro Heli – 400DF – 15T pinion
Direct drive – 300DF on 1 pound or lower weight Wings, Depron Jets, 400T – Overlord Wing, Slow and high thrust wings on 8 inch prop, 400F fast and agile on 6×4 prop 3S, 400DF – very fast on 5 inch prop – less thrust, 450FT – excellent on any size plane 7 or 8 inch prop, 450TH – extreme for over 100mph on wings and jets on a 5-6 inch prop.
450TH is an extremely powerful motor, which is most popular in the T-Rex at 3S on a 13T pinion 3.17mm pinion for 2600 RPM, 4S on an 11T pinion for upto 3300 RPM. This motor is available in 3.17mm axle tractor, 2.3mm tractor for gearing in large planes or extreme performance on medium size planes and 3mm pusher format for over 100 mph in Jets and Wings. The 3.17mm bell is locked on the motor.
450F is also and extremely powerful motor that is slightly more versatile than the TH since the bell is removeable on all models. This works well on the T-Rex with a 10T 2.3mm pinion, the same bell runs well geared in airplanes. For a direct drive motor please consider the 450FT.
450FT is a modification to the 450F that you can perform yourself by purchasing a medium speed bell. Pull the 450F bell of and slide on the new medium speed bell and you have just converted the 450F from 3450 KV to 2250 KV. Now you can run 7 and 8 inch prop with authority on your plane, jet, wing.t
450XT drive with upto 11 inch propellors. A 9×9 properllor is excellent for speed. If you have a large 3D airplane – this is the motor for you.
400DH continues to be an extremely popular motor for the Shogun and T-Rex. I recommend an 8T pinion on the shogun, and 9T on the T-Rex. This will provide longer flight times than the 450TH and 3D capability, but not the same insane power that the 450TH provides.
400DF is ideal on the Century 3D Pro Helicopter on a 15T Pinion. This motor is also well liked on pushers (Jets and Wings) and geared is very powerful. Swap bells to go from 3mm pusher to 2.3mm tractor for gearing in a 400 size gearbox.
400F is the same KV (RPM Speed) as the 450FT and very efficient, ideal with a 6×4 prop on a direct drive plane, jet or wing and excellent geared 3:1.
400T is very popular in slope soarers, park flyers and warbirds.
300DF is well liked in depron jets, wings and planes under 16 oz’s and although not 3D, can provide high speed direct drive, or can be geared 3:1 for running larger props and planes.
400ST is ideal in direct drive planes and 3D flying planes
300ST is for very light weight and ideal in light weight planes and 3D planes.