I tried some 100 octane gas today(CAM) I got from a local gas station for $3.88 a gallon, didn't really notice any difference, but then again I don't know if there is a difference....Is this gas good/bad for the engine? What are the advantages?

 

The pupose of high octane is to combat detonation/preignition in built-up high compression motors. If the motor doesn't need high octane, then its really not worth spending the extra money. the factory compression of the DS is 9.7:1, and its designed for use with 91 octane or higher. 87 octane will cause problems, while 100 octane doesn't hurt, but won't necesarily help anything either. Guys that raise compression to 12.5 and 13 to 1 need the race gas or pre-ignition from excessive combustion heat will result. Octane rating describes the fule's resistance to burn - the higher the octane the cooler.

 

wat kind of problems will 87 cause?

 

Excessive combustion and exhaust temperatures, increased chance of pre-ignition, more internal wear, all result from too low octane.
Never run an octane lower than a manual recomends, regardless of what kind of vehicle it is. But don't expect any real gains from anything higher either. Its all about the combustion heat - it needs to be controlled by the incoming fuel/air, and correct octane is vital for that. The higher the compression, the more heat produced, so the higher the octane needs to be to control it.