What turbo belongs on a AI-460 and an AI-427? S300 or S400? My research says an etech should have a S300 on a 350-400hp and a S400 on a 427-460. That is all I know. I realize the AI is not an etech but similar. My engine is an AC-427 converted to either an AI or etech engine. I'm not sure which. Its a very long story. I appreciate the help in advance and love the site. This site helps the working class diagnose our truck troubles and keep us earning the money to feed our familes.