new in the world of electrics, just a few e-revo questions

[BrianG]

There are a number of factors that can attribute to runtime; gearing, weight, drivestyle, terrain, etc.

Are you sure that both setups are using 4s 8Ah lipos? Because if one uses a 4s pack, and the other uses a 2s or 3s pack, there is a substantial difference.

It takes power to run these. Power is current X voltage. If you run lower voltage, you will need higher current to create high power. Higher current reduces runtime. Running a higher voltage setup requires less current for the same power, so runtime increases.