I'd imagine with a TiAL housing and a bit of work in the turbo you could get that 17 to spool just as quick, or quicker than your other turbo.
How much compression are you running?
How much boost are you making?
IMO you will wanna be a bit careful with that new turbo until you get a handle on what exactly you've got for compression. Also, there is some tuneability (is that a word?) With your plenum sizing. With that being said I'd bet that pipe design will yield better results at this point that plenum design will. I bet that fugger is a riot on the street! My turbo bike was the funnest bike I've ever owned!
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