I am looking to upgrade the stock turbo on my 4bt. Its an HC1 that I put a 12cm2 turbine housing on. I just turned up the full power screw a bit and am getting some smoke even at full boost. Gillette Diesel offers upgraded compressor housings. I need to stick with the 3" inlet, and they have a 52mm upgrade. I also have a HC1 from a non-aftercooled truck (1990), and am wondering if that would be an upgrade over the stock 4bt turbo. Does anyone know the stock size of the 4bt turbo? Based on info from Gillette diesel website, the stock turbo on the non-aftercooled dodges are 50mm.