If you have the stock pipes, thats when you need the bolt-on adapter. If you have an aftermarket upper IC pipe, which i would assume you do if your running 20+ psi, then you need the weld on flange.

However, it is possible to bolt up the HKS to a greddy/1g flange thats already welded on, if thats what you already have. Let me know, I will make a little diagram showing you how. Kinda ghetto, but it works fine.

Thats how mine is, and I've never had any problems.

Edit: And last time I checked, Racing Zone in Tampa had the HKS SSQ for like $220...Which is a really good price, even compared to internet shops. I dont remember if that included the adapter, but you shouldnt be hooking this up to your stock pipes anyways.