| Since you mentioned Sigma, I expect you'd be in good hands. Neil Spalding can probably advise you better than just about everyone on this board.
In general, to get more power, you need bigger diameter throttle bodies. Whether you need one or two injectors depends on the how much fuel you can dump in the time between strokes at max RPM. I doubt, you'll run out of fuel on an 853. Neil will know, ask him. | 
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