If you're fully stock and you only open up your exhaust, you'll take a hit at the top end (as I experienced @ the dunes).
The throttle seemed to respond a bit better and engine stalled at a lower RPM.
If you take the noise baffle off of your snorkel, you'll definitely need to re-jet.
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Here's a list of what I've done (besides adding armor) all prices don't include tax or shipping & handling and are in US funds
(Free) cut out pea-shooter from stock exhaust pipe
(Free) remove snorkle cap and cut holes in top of airbox
($5) 140 Main Jet (has not been trail tested, may need 145 or 150)
($0.20) two No.4 washers to raise needle height (has not been trail test, may need to use only 1 washer or 3, it definitely needs a washer)
($5.00) speaker fabric to act like an "outwear"
($22) Uni filter
($208) 22Hx12Wx10wheel Realtors on Douglas Red Labels 0.190
($14) 13 tooth front sprocket
($0.78) 7/8 inch clip to hold on new sprocket
Total ~$255
The re-jet, exhaust hack, Uni filter and air-box hack (Total:~$32) have definitely helped the Z's low end. It seems to stall at a much much lower RPM. It hits the rev limiter a bit faster now (according to my butt-dyno)
You can spend $70 for the alba K&N and outwears + $60 for a dyno jet kit or you can do what I did for 1/4 of the price.
If you have any specific questions, feel free to PM me or reply here. I always check threads I've posted in.