I did this before on my stock 660, when low speed I didn't feel any diffrent, but the engine become more power at high speed 60km/h~120km/h. Funny things is when a car block front of me, this air intake become no effect or useless to the engine and back to normal.
But at the end I don't use this air intake anymore, why ar~? b'cause:
1) The air filter are more easy to get dirty then before, and many tiny rock stuck on the air filter.
2) This is part is really stupid one I tell you ^_^, when it was raining.... you know what will happen lar taiko~!!! ha ha ha ha ^_^