You might be able to. It also depends on the servo load. If you are running one lower power/speed servo, you should be ok.
However, I always recommend a UBEC over 3s or 8 cells. The ESC will just heat up more because of the BEC and that's the last thing you need. Think of it this way, running 4s on the built-in BEC with a 1A load will force the ESC to dissipate over 9 watts. That's really a lot.
ok, thank brian.
i will be running servo's of the digital kind with 8kg of torque or even better.
so i'll need the bec then.
i tested a motor of my truck(stocker) and on 7.2volt it only did 15k rpm.
so i'll be runnig 4s lipo or or 12 cells NI-MH anyway.
then it will do about 40~45kph.
thats good for me.