Roush Best way to achieve more HP

Advice on upping the HP on the 05-09 ROUSHCharged mustangs .....

Just about any mod to gain HP will void your warranty, even RPP parts.

With a 2.57 pulley, CAI and some tuning expect 420- 450 rwhp 390-410rwtq. But note, the CAI will void the warranty. At least, that's what I understand to date.
I'd confirm with ROUSH if you're that concerned with a warranty.

Yes any mod will void your warranty...

I just got mine tuned with the VMP 500HP kit. All I have to say is WOW!!! The car should have come like this from Roush!!!!

After the tune, the car's drivability greatly (100%) improved!! Its sooooo smooth its rediculous...and I didn't have any issues before. The power is just intoxicating; its pulls so freakin hard!!!

Don't waste your time with the Roush CAI its junk...go to VMP and get the intake and smaller pulley (the 500HP kit)...you will not regret it!!!

I say wait until the warranty is up just to be safe. Then yes swapping the pully will make a difference. Probably not enough to push you to 500. However there are a lot of other minor upgrades that can get you there.