i wish the rb26 guys would chime in. From what i remember it's a direct bolt on. Verify it by checking it's flange size such as t28 or t3. Anyhow, they pump out good air for the 26 in twin application. If you did it single turbo app. it wouldn't do much for you at all. Very reliable turbo. It is if i'm correct the silvia s15 turbo as you stated. do an ebay search and get more info about it. Normally people tend to go big single turbo and manifold. Allows more room and more power but can be laggy if you don't check your compressor maps.