power brake vacuum

I just put in a different cam into my 340 and it seems to have affected the power brakes. They work but I have to push harder and seems they take longer to build up enough vacuum. Is there any thing I can do to get more vacuum to the brake booster? I thought about adding a vacuum reservoir, but before I did that I thought I would ask in case anyone has had the same problem. I may not be on the right track,not sure