The explosives would have the same range and damage as before, since spells only do what the description says, no more or less. And there is no mention of explosives (for which there are no real rules anyway). The description increases the size and weight of an object, but there is no other effect.
There is a rule for increased weapon damage, although it could be argued that this has to do with both the increased weight of the creature it exercises and the size of the weapon itself.
That means … if the explosive is homebrew, a DM can make his own decision. If the explosive radius is 5,, simply increasing the explosive would automatically increase the radius (if you look at it as a ‘aura’ around the object). Adding an additional 1d4 to match the increase in weapon damage is reasonable.