Ok, well I've finally purchased a real HKS Hi Power exhaust. I used to own the ebay X02 exhaust. I always used to defend the X02 till the end vs the HKS Hi Power. Now that I have owned both and heard both MANY MANY MANY times I can make an honest conclusion between the two.
Quality: The piping itself on the HKS vs the X02 look pretty much identical to me.. Feel the same, looks the exact same. The flex joints also look and feel the same to me as well.
Now the welds is where the HKS wins this battle IMO. The welds on the HKS look more refined and professional, seems like the HKS put a decent amount of time into welding this specific exhaust together. Don't get me wrong though, the welds on the X02 look good, just not as refined as the HKS..
As far as exhaust tips, HKS wins hands down.. Tip on the X02 look like ***.. IMO the people that make the X02 should either include real titanium tips at a slightly higher price, or make the tips just plain old stainless steel so they down look brown after a little while of usage.
Fitment depends on how you install the ehxuast from what I've seen. When I took my new X02 to the shop to have it installed they rear left tip was hitting my bumper and it actually burned it
I was pretty pissed off and for the longest time I thought thats just how the X02 came until a friend bough it off me. Once we put it on his car the X02 sat perfectly flush.. Guess I took it to a hackjob shop. Fitement on the HKS has always been dead on from what I've seen. It was good and flush the first time it was installed.
Now there are some out there that say the X02 rusts and the quailty goes to crap after a while.. Let me assure you that ANY exhaust driven through salt and snow will rust after a while especially when its negelected and not washed down properly.. The salt will chew through that metal. I've seen and hear people complain about fitment on both X02 and HKS. Really, I just think that the people who had rusted X02's were just negelecting the underbody of the car and never cared for cleaning the underside. Thats all. Here's another goody.. After about 10-15K miles of usage both exhauts look identical, they turn into the gold/brown/bronzish color it just appears that both exhausts are made of the same metals.
Sound: Sound is all about you're opinion, do you like the more high pitched/almost sound or would you like a deeper more muscular sound? All up to you.. With test pipes both exhaust rasp HARD, and both exhauts make this weird metallic sounding rasp too I used to think only X02 did this. I will say though that the X02 has a little more drone to it on the highway with test pipes. Not much more but its there.
Performance: IMO the X02 wins here, its the exact same design as the HKS but the X02 has slightly bigger piping measuring 2.5 inches where as the HKS is around 2.35 inches. The X02 always just felt like it had more power to it, especially with test pipes. Thats where the X02 wakes up and I guarantee you'll feel a noticable difference.
Overall: For the money the X02 is better hands down.. Clearly they stole the design off HKS and made a total cheaper product.
I'll say this over and over and over.. The HKS exhaust is definitly not worth the $1500 price tag they give it. Not even close.
If I had a choice to pick between the two for free I'd choose the HKS. Why? Several reasons.. Cleaner, nicer looking tips. Nice good brand name. Sounds great (I still prefer x02 sound) but the HKS still sounds sexy. Last reason, it's just sort of shameful to have knock off parts on your car. Especiall when you're at a car meet and when the guy next to you has the real deal and pretty much makes you looks cheap in front of everyone.
Hope that was good enough for you guys.. I too would get mad if I bought a $1500 exhaust and someone else but the same thing for $400 and it performed better.
EDIT: Forgot to add that the X02/ebay replicas come with 2 extension pipes so you can make the exhaust work on a Z or a G.. The beauty of this is so if you ever wanted to sell or trade your X02 you can sell it to people with 350z's too.. Or use the extension pipes to work on other exhauts.. Hang them on the wall, make pipe bombs?? Idk lol.