In essence it's a better design doing away wit hthe siamese ports on cylinders 3&4....but there's plenty of big power ones on the standard manifolds so can't be that big an issue. I bought one when they first came out, didn't actually dyno the car with it on to see the difference but i'd have been surprised if it had made a massive gain, the only gripe i had with mine was it kept blowing manifold gaskets which i eventually worked out that the flange wasn't flat! The way they're constructed there is also a slightly larger gap between the turbo housing and the no.4 primary, so should be able to fit a lrager turbo on without having to use a spacer. I never got round to having mine refaced so went back to the standard one lol, still sat in the garage somewhere gathering dust