To be quiet honest if the core voltage was anywhere near 1.8v ydoumus.
You would of seriously over volted an FX cpu without much doubt and rendered it completely dead.
The maximum most boards will allow you to set the Vcore of the cpu is about 1.6v total.
With most people being able to run an FX 8350 cpu at around 1.4v when overclocked to 4.5 or 4.6 Ghz.
There are a number of things that can prevent a FX 8350 cpu reaching a target speed of 4.5Ghz speed.
It is not just down to the cpu it`s self sometimes, it can be down to the fact of what chip set the motherboard is using in the AMD line of custom chips.
For example a 990FX board in a lot of cases performs better at overclocking the FX 8350 yielding better overclocking frequency's.
In cases like this it does not matter how much voltage you try to give to the Vcore of the cpu it`s self.
The chip set of the motherboard is just not able or has enough overclocking scope to hit a frequency of 4.5Ghz.
Likewise memory can be another reason.
And also how the cpu is cooled and by what type or brand of cpu cooler.
If you list the brand of motherboard you have and the Motherboard chip set model numbers it will tell you roughly if the motherboard is the cause as to why you cannot overclock the FX cpu by much.
On average with a good motherboard, with a FX 990X chip set on board and good cooling most FX 8350 cpu`s at around 1.4v core setting will overclock about 600Mhz over the stock frequency providing you also have a good enough cpu air cooler, or water loop fitted.