You guys need to be warned to be VERY CAREFUL when playing around with changing the exhaust housings on the turbos - especially the bigger singles.
True, by adjusting the housing size, you can get the turbo(s) to spool faster, but it is a tricky endeavor as it also cause more heat to be generated.
As soon you start changing the exhaust housing, your chances to lift a head increase ten fold for every millimeter you change it.
Do you honestly think the kit manufacturers use an exhaust housing to lag the spool on purpose? You can't honestly think that when the design kit - they don't want as low a spool time as possible - they use what they use because it RIGHT and the pros do not outweigh the cons on a mass production type of thing.
Do some research and be sure of what you are doing when you start playing around with exhaust housings...