Freelancer ID gets 75% powercore if you equip non civilian guns. Stick to the civilian ones. They are mostly sold on police, corp, junkers and freelancer bases, if you need guns with different stats.
About engine, try visiting a Freelancer base. They have a lot of engines with different colors to suit your taste. Don't buy Gallic engines if your ID is Sirian. They'll give you powercore nerf too. Use the Black Market version.
