rca

I have a a 1980 Fiat spider which i bought a Sony Xplode cdx-s2000 deck and Component type R speakers and Boss 800Watt amp, I have alot of engine noise picked up, the trunk is mounted in the trunk and the cable which runs the power wire from batt to engine is on the left side of the car so i ran the rca,remote wires on the right.  I was told that i need a Ground loop and a new rca cables due to the fact that they appear to be cheap speaker wire cables wraped in clear insulator. 

My question is what type of rca wires should i get is there something i have to calculate to figure sizing or what needs to be in the cable to remove as much of the engine noise as possible? 

Also in terms of ground loop is there any specific ground loop cables i should look at?

I am not looking to spend a ton of money on these things its not a $1000 system, which you would be looking for crisp audio, just something to take the engine noise and decent audio.  The car is a rarely driven car and a convertible the point of the system was just to have the ability to hear the music while cruising on highway aside from the old sytle radio and only front speakers which i could not hear anything.

Since the battery is located in the trunk the ground is directly from te battery to the amp probly 12 inches long.  Also what is the problem with having a ground loop?? Whats the downside i have done a search of the loop but haven't really seen to many bad report because of it , which i did wonder why?  Any brand i should look at? The car is old but i put new ground cables all the way through and if they weren't new they were cleaned and resoldered.  Cars has thickwires in general so ground should be decently good.

As far as what is bad about them?  I have no idea.  it was just policy in my shops that we tryed not to use them.