so long story short gonna be running losi 8ight e 2.0 buggy with the tekin rx8 1900kv combo and a spektrum 3s transmitter. no my problem cuz i know nothing bout all these numbers. i wanna purchace and run the spektrum 6100 servo which is hi voltage and high torque and says is rated 7.4 volt. now if i run this car on 4 cell lipo at 14.8volts does this mean this servo wont take it cuz its 7.4 volt. i dont know sorry. or maybe i have to run what people are calling a bec. any help would be awesome thanks guys

Without an external bec the rx8 speedo will supply 6V to the servo through the receiver. On 6V it will be a bit slower and weaker then on 7.4, I would try it this way first. If you are not satisfied and want more from it, then you need an external bec that will provide 7.4V, installing it is simple if you can solder well.