Mine actually feels quicker with the new induction kit fitted and sounds sweet. Even noticed when cruising last night I was getting 37mpg when I was getting about 33. But might not be related.
I noticed an mpg improvement last night after fitting mine and it's not even shielded yet.
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It will be can't recall the figures over a standard box compared to a sealed heat shield but it is a nice chunk of difference.
Only tip i'd advise is the sfs big bore one, get as much air in as you can