Difference b/w AEP and AEG
 

what is different between AEG and AEP.

and last, what is AEP anyway. Airsoft electric Pistol?

AEG - Automatic Electric Gun - Usually full sized electric guns (AK's, M4's, G3's...)
AEP - Automatic Electric Pistol - Usually pistols and small SMG's

basic, both do same thing? but with different name?

Not exactly. AEP mechboxes are about half the size of normal mechboxes. They're less powerful as a result.

Plus not as riliable as a well shimmed and maintained geabox (AEG E.G V2,V3...)

And to find aftermarket parts, just search hard, all I can say...

Aftermarket internals are readily available if you know where to look.

The unfortunet thing about the AEP mecbox is that it has its own special parts, so parts will not be interchangeable with that of regular mechbox parts. As The Staint stated due to their smaller size they have a reduced output for power. Even with fully replaced and upgraded internals you will not achieve any form of output close to that of a standard aeg.

I believe even a fully upgraded AEP which costs as much as pimping out a full sized AEG still only shoots around 300fps. I remember someone here on ASC investing something like $750 in parts in a TM MP7 and it ended up shooting 290fps or something.