But what I am thinking now is it shouldn't matter which motor you have if they are geared for the same speed and battery is the same voltage.

Yes it should, because the weight of the motor (neu is lighter) and it's always better to run a lighter car (in 1:8 scale everybody look for a lighter package).

IMO the 2-3 ounces difference in weight would be mostly negligible. On an 8 pound vehicle 3 ounces is only 2% of the total weight.

Oh well, maybe someone smarter than myself will post later on and make heads and tails out of this.

If possible, run the neu on 4s and 5s, geared for the same speed, then compare temps/controlability/runtime- ideally with the same spec batteries, or atleast the same mah.. That would make for an interesting comparison.

The 5S setup would give cooler temp for sure, but he want to run it only on 4S.

If both motors were equal in all aspects except for kV, then that statement would be 100% true. Unfortunately, they differ in lots of ways: weight, overall efficiency, overall design, parts used, etc. While each difference may be small, they are all present at all times.

The motor with the higher kV will be less efficient at the same (vehicle) speed as the lower kV. The motor that weighs less will make the vehicle more efficient overall. A higher motor speed imposes lower mechanical efficiency on the motor, as well as lower electrical efficiency.

Based on all that, I would chose the Neu 1512 1.5y. The lower kV will help motor efficiency, and the lighter weight will help overall vehicle efficiency. If you are only gearing for 40 mph I don't think you will notice any difference in driveability, either.

But how much difference in efficiency are we talking here? a fraction of a percent? one percent? 5-10 percent? That is where the eagletree would be nice to have.

Yeah it would be nice to know exactly how much... If it turned out to be negligible that would be OK with me! :lol:

Have to run your Neu motor in a bomb calorimeter (anyone remember high school chemistry LOL)