273 Engine intake upgrade turned sour

Heard it was designed for RVs. I only have it because the mechanic who rebuilt the engine for my parents nabbed the unique '65 heads and original 4 barrel manifold. It works well for me up to 4000 rpm. That is where the pull starts to fade which I don't like. Must be something else holding the engine back. Can't believe a manifold would fall off like that. A Carter Competition Series 625cfm I ran for a while added noticable power and an additional 500 rpm of pull. To much Carb for a stocker though. Should be a great choice for your application. Member: 69 Cuda 440 wrote a piece on it Dec. 2014. I will give it a chance after my cam change and a 600cfm Holley. You see, I am going for passing power. :)