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If you run it on a 2.5 you might get a bit more, but on a 2.0 it'll be pretty much bang on the 450 as said (subject to you having the right supporting kit as well). I used to have one of their early versions of the RCM 450 (10 years ago!) on my 2.0 and it was dynoed back then at 437Bhp. I'm sure that improvements were made thereafter plus things like ceramic coating etc.