More cam?

I ran a 228 hughs roller cam in my 410 stroker and have just recently change it to the next size up 234 @ 50 thou. It now idles smoother and has the same vacuum 14 inches at 775rpm. I used to run try y headers 1 5/8 to inch 11/16 to 2.5 collectors and exhaust. I have changed to larger headers 1 3/4 to 2 inch and 3 inch collectors and exhaust. Old set up ran 11.4 in 3300lb car and are hoping for a low eleven with these imorovements. by the way last year on a run it got 21mpg going down south with a 3.91 diff ratio but a five speed manual box.