General Magneti Marelli for 1.2 500?

[Murano16v]

Magneti Marelli rear silencer for 1.2 as on Shop4parts claims to give another 4hp. What does anyone think? Likely or not? Looks quite subtle, which is good and not supposed to be noticeably noisier.
Any more oomph would be most welcome on the 1.2.

 

[Venters]

seems like a large gain for just a rear silencer.

 

[Murano16v]

seems like a large gain for just a rear silencer.

That's exactly what I thought.