GM Duramax 6.6L LLY 400-800 HP What separates the Silver PhatShaft from the Super PhatShaft is our new technology 74mm turbine wheel. To improve on the Super PhatShaft turbos we needed to improve performance at a lower rpm range and we needed to reduce compressor surge. We came up with the 74mm turbine which is the latest in turbine trim design technology. The new trim design transers exhaust gas energy more efficiently than any other turbine on the market. It also allows for better exhaust gas expulsion which results in lower EGTs and quicker rotor acceleration. Above all, the 74 mm turbine whell eliminates turbo surge and lowers EGTs.