Well I’ve converted my SG1604 to brushless. It’s now running a 4500kv motor and 35A esc.
It’ll handle 3S but it’s more fun and driveable on 2S. That said it’s one of the EASIEST brushless conversions I’ve ever done, it’s also pretty cheap to do with the esc/motor combo costing around $32, the radio with gyro $30 and a new 3 wire servo $12
You need a new radio and servo if going brushless as the stock SG1604 has a combined esc and receiver and a five wire servo. So if you go brushless you need a new receiver to mate up with the ESC and receivers only take 3 wire servos so that needs changing as well.
Here’s links to everything I used in this conversion:
Here’s the car – https://www.banggood.com/custlink/mGmh99WeSE Or get the SG1603 pickup here – https://www.banggood.com/custlink/33vd89WgSL
Here’s the radio – https://www.banggood.com/custlink/mD33VJz8zU
Here’s the brushless combo – https://amzn.to/2ZsCiBy (3600kv as 4500kv out of stock)
Here’s the servo – http://ebay.us/MHEIek