My understanding (and this is including responses over at priuschat) that it's really just there for noise.
General consensus is that it makes the intake noise a little ballsier under WOT.
I haven't read any negatives though, so while it might not do much, it's not going to hurt anything (unless you spray the cone at the carwash).
General consensus is that it makes the intake noise a little ballsier under WOT.
I haven't read any negatives though, so while it might not do much, it's not going to hurt anything (unless you spray the cone at the carwash).