Im wanting to purchase a full dual exhaust HKS HiPower exhaust for my 1990 300zx.

What online retailers would you suggest?

 

Friend of mine likes Burtons Auto Performance. They backed their 'it will definitely fit' warranty when a system he bought didn't fir. But most retailers can do that. It's factory made so you may as well shop for price first and compare warranties and reputation. I would avoid Ebay but that's just me.