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Ill answer as it seems nobody cares to answer this because most probably think it's a silly question lol no offense. I have had Fp Red, EF 2.5, Ef 3 and imo they all sound similar. The Red might have been slightly wilder with sound but the EF 3 n Red sound pretty similar. The Big thing here is the intake choice you go with. Short rams are always louder, assuming you dont use a box intake. Gluck

 

Does the EF2.5 you're buying have the anti-surge compressor cover?! That will make it sound a little different compared to the standard compressor cover.

 

I believe the amount of flow going to the intake compressor has the majority to do with the "sound" from the turbo. The style of intake also can play a factor in the "sound". A larger turbined wheel turbo will have a different sound than a smaller wheeled turbo.

Btw, most people usually pick their turbo with power levels in mind. Not trying to be a *****, but kind of an odd choice style to pick a turbo