ICS V2 Gearbox vs. PDI 130%
 

Will the gearbox beable to handle the abuse a stronger spring will apply to it. If have peaked around and signs mainly point to yes, but it never hurts to make sure. Also will an 8.4V battery (3600mah) be able to turn the motor?
Thanks

PDI 130% is pretty soft spring. Your mechbox will be fine. 3600mah is more than enough to crank PDI 130%.

You still need to upgrade to metal bushing. I run my ics m4 with a 150% pdi (the good ones), metal bushing and 9.6v 3300/ 1800 mah batteries.

I do have metal bushing, new shims and a guarder hop-up bucking sitting here, just figure if I am going to crack open the gearbox, might as well go all out. I think I am going to go with the pdi 140%. I am looking for about 370fps, I am just going off that spring comparison chart in the stickys.

PDI 130% and PDI 140% both are fine. Just don't get PDI 150%. I got one about 2 years ago and it was fine but later one people started to report getting anything from really low to insanely high FPS with those springs.

prometheus MS110sp should land you 360fps. add a tightbore, spring guide and so on and your around 370fps...high enough to outrange stocks but safe below 400fps.

PDi springs are basic coils, but the prometheus are irregular pitch and far more consistant.