I have the XTR Stage 3 airbox, it makes a huge difference, but I cannot compare to the Stage 2, as I just went to Stage 3. I think Stage 3 has a wider improvement in the rev band.

I take my bike offroad, and just remove the side panels and tape up the sides of the airbox. It doesn't make any noticeable difference to performance,......but then again, I'm offroad then.....

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2008 XTR Mods : DNA Stage 3 Airbox, PC111, Carbon Cans Ovals, Steve Ruth built XTR734cc Big Bore with - High Desert Dyno (HDD)/ Cuervo Racing Gas Flowed / Ported Head fitted with +1mm Valves & uprated Springs, HDD 5050 Camshaft, HDD +3mm Throttle Body, CP 105.5mm 11:1 Piston, Custom Mapping, Piasini ECU, Renthal 613-01, Barkbusters VPS, Pivot Pegz, Touratech Bashplate, Foam Grips, Kev's O2 Sensor Mod, Kev's Extra Coolant Cooler, Wilbers Progressive Fork Springs and Rear Shock