I wouldnt use anything higher than a 120 spring unless you replaced your gears with a high torque gears and maybe a higher torque motor but most motors can handle 120 springs. I wouldnt go very high power cause the v2 gearboxes arent very strong in my opinion. Thats one gearbox I wont own again,lol.. I have blown them out with 110 springs and a 10.8v battery. Three gearboxes to be exact. What are wanting to get out of it by chance? And just like a bolt rifle, the first things to mess with are the hopups and buckings. I dont know a whole lot about aftermarket parts like I used to. Too many new parts out and I am out of date,lol..