well they have different part #'s (maybe colour) the xn85 had heftier cylinder studs, but had the same bore. sorry thats all i got.The xn85 while looking like a gs650 motor had different cases (because they changed to plain bearings as opposed to roller bearings because of the turbo)
here's a good site
http://www.xn85turbo.com/index.html
gerry
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