ZX28 I had that dilema not to long ago. With 500hp at the crank and n2o 1 3/4 longtubes are the way to go. Limited fabrication skills and next to zero funds forced the use of 1 5/8 blockhugers. I used edelbrocks new blockhugers with 3" J colectors. The fact that the colector flange is not right up on the primary tubes and dump smoothly into a 3" pipe, may help flow over other blockhugers. If edelbrock ever makes them with 1 3/4 primaries I'll be the first on line for them. That said, I did have to cut J colector at its loest welded section and extend the colector 2 1/2" to clear the bar that ataches to the control arm.