Put in much bigger pipes. More horses?

Hello Hudson community, been away but, while my clutch disc is being recorked by Hudnutz I thought I'd pose another round of possibly significant questions. First, on my 28 Hudson exaust manifold there is a separate piece along the exaust system that houses the butterfly for blocking he exaust to warm the gas via the tube to the manifold. The previous owner had brazed a flexable tubing to this piece to make a quick exaust system. I removed the rusted remnants and exposed inner threads. Now, logic suggests there was a piece there before the pipe as the diameter is approx. 2 1/4 whereas the tailpipe bracket is 1 1/2.With the lack of the proper piece I had a custom pipe made that snugly fit into this piece which I sealed with muffler sealer compound. It worked just fine. I measured the space available for a muffler and bought a round in stock muffler then while the clutch was working went to a muffler shop to have a tailpipe custom fitted. That said, the pipes from the motor are 2 1/4 diam.,much larger than stock. This question is (and the motor runs fine) did I gain some horsepower with the larger pipes or is it negligable? Next I'm discovering much use of aluminum on my car, the clutch disc, the transmission housing. I thought this was a little early for alum. if not seems Hudson was way ahead of its time. Are there any other alum. parts on this car? If they could cast an alum. housing for the trans well then why not rims? seems a wasted oportunity. Well that's it for now. Love to hear some comments or facts from all you techs out there. Sincerely Phil